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  THE

  REASON WHY:

  A CAREFUL

  COLLECTION OF MANY HUNDREDS OF REASONS FOR THINGS WHICH, THOUGH
  GENERALLY BELIEVED, ARE IMPERFECTLY UNDERSTOOD.

  A BOOK OF CONDENSED SCIENTIFIC KNOWLEDGE FOR THE MILLION.

  By THE AUTHOR OF "INQUIRE WITHIN."

  This collection of useful information on "Common Things" is put in
  the interesting form of "Why and Because," and comprehends a familiar
  explanation of many subjects which occupy a large space in the
  philosophy of Nature, relating to air, animals, atmosphere, caloric,
  chemistry, ventilation, materia medica, meteorology, acoustics,
  electricity, light, zoölogy, etc.

  NEW YORK:

  DICK & FITZGERALD, PUBLISHERS,

  No. 18 ANN STREET.




PREFACE.


We are all children of one Father, whose Works it should be our delight
to study. As the intelligent child, standing by his parent's knee,
asks explanations alike of the most simple phenomena, and of the most
profound problems; so should man, turning to his Creator, continually
ask for knowledge. Not because the profession of letters has, in these
days, become a fashion, and that the man of general proficiency can
best work out his success in worldly pursuits; but because knowledge is
a treasure which gladdens the heart, dignifies the mind, and ennobles
the soul.

The occupation of the mind, by the pursuit of knowledge, is of itself
a good, since it diverts from evil, and by elevating and refining the
mind, and strengthening the judgment, it fortifies us for the hour of
temptation, and surrounds us with barriers which the powers of sin
cannot successfully assail.

It is not contended that the mere acquisition of knowledge will either
ensure a good moral nature, or convey religious truth. But both
religion and morals will find in the diffusion of knowledge a ground
work upon which their loftier temples may discover an acceptable
foundation.

The man who comprehends the order of Nature, and the immutability
of Divine law, must of necessity bring himself in some degree into
accordance with that order, and under submission to the law: hence the
_tendency_ of knowledge will always be found to harmonise the fragment
with the mass, and to subvert the evil to the good.

The troubles of the world have arisen from the want of knowledge,
not from the possession of it. And in proportion as man becomes an
intelligent and reflective being, he will be a better creature in all
the relations of life. If these benefits, vast and incalculable as they
are, be the real tendency and result of knowledge, why is ignorance
allowed to remain, and why is the world still distracted by error?

It is because the moral and intellectual qualities of man are, like all
creations and gifts of God, the subjects of development, whose law is
progression.

We can aid human improvement, but we cannot unduly hasten it. Whenever
man has sprung too rapidly to a conclusion, he has alighted upon error,
and has had to retrace his steps.

The greatest philosophers have been those who have clung to the
demonstrative sciences, and have held that a simple truth well
ascertained, is greater than the grandest theory founded upon
questionable premises. Newton made more scientific revelations to
mankind than any other philosopher; and his discoveries have borne the
searching test of time, because he snatched at nothing, leaped over
no chasm to establish a favourite dogma; but, by the slowest steps,
and by regarding the merest trifles, as well as the highest phenomena,
he learnt to read Nature correctly. He discovered that her atoms were
letters, her blades of grass were words, her phenomena were sentences,
and her complete volume a grand poem, teaching on every page the wisdom
and the power of an Almighty Creator.

When he observed an apple fall to the ground, he asked the "Reason
Why;" and in answer to that enquiry, there came one of the grandest
discoveries that has ever been recorded upon the book of science. With
that discovery a flood of light burst upon the human mind, illustrating
in a far higher degree than had ever previously been conceived, the
vastness of Almighty Power.

Why should not each of us enquire the "Reason Why" regarding everything
that we observe? Why should we mentally _grope_ about, when we may
_see_ our way? When addressed in a foreign tongue, we hear a number
of articulated sounds, to which we can attach no meaning; they convey
nothing to the mind, make no impression upon the in-dwelling soul.
When those sounds are interpreted to us, in a language that we can
understand, they impart impressions of joy, hope, surprise, or sorrow,
because the words convey to us _a meaning_. In like manner, if we fail
to understand Nature, its beauties, its teachings are lost. Everything
speaks to us, but we do not understand the voices. They come murmuring
from the brook, trilling from the bird, or pealing from the thunder;
but though they reach the ear of the body, they do not impress the
listening spirit.

Every flower, every ray of light, every drop of dew, each flake of
snow, the curling smoke, the lowering cloud, the bright sun, the pale
moon, the twinkling stars, speak to us in eloquent language of the
great Hand that made them. But millions lose the grand lesson which
Nature teaches, because they can attach no meaning to what they see or
hear.

"THE REASON WHY" is offered as an interpreter of many of Nature's
utterances. Great care has been taken that these interpretations may
be consistent with the latest knowledge, obtained from the highest
sources. If the author finds that his work if accepted for the good of
those who seek not only to know, but to _understand_, he will make it
his constant care to read the Book of Nature, and to add to the pages
of this volume whatever interpretations the progress of enquiry and
discovery may demand and supply.




INDEX, AND INDEX LESSONS.

[Pointing hand symbol] _The numbers refer to the Questions. The Index
Lessons do not correspond with the Chapters, but are designed to bring
together in their alphabetical connection, all the Questions and
Answers upon each particular subject included in the work._


  LESSON I.

  Acids, vegetable, whence are they obtained, 1256

  Actinism, what is it, 552

  Actinism, what effect has it upon vegetation, 559

  Actinism, at what season of the year is it most abundant, 560

  ærial spectra, what is the cause of, 527

  Affinity, what is the attraction of, 777

  Air, why do we breathe it, 4

  Air, what is the composition of it, 12

  Air, what is its state after it has been breathed, 13

  Air, is that sent from the lungs light or heavy, 14

  Air, is it a good or bad conductor of heat, 150

  Air, why is a still summer said to be sultry, 171

  Air, why does it feel cooler when in motion, than when still, 175


  LESSON II.

  Air, when is it hot enough to destroy life, 179

  Air, why is it often excessively hot in chalk districts, 219

  Air, is it heated directly by the sun's rays, 221

  Air, why does it ascend the chimney, 240

  Air, why does it fly through the doors and windows towards the
    fire-place, 241

  Air, what does the motion of it in our rooms illustrate, 242

  Air, why does it become charged with watery vapour, 346

  Air, when is it said to be saturated with vapour, 430

  Air, what proportion of water is air capable of holding in the form of
    vapour, 431

  Air, what is its weight relative to that of water, 647


  LESSON III.

  Air, which is heavier, dry or vaporised, 697

  Air-pistol (or pop-gun), why does pressure applied to the handle propel
  the cork, 854

  Air-pistol, why must the handle be drawn out before the cork is placed
    in, 855

  Air, why does fresh impart a healthy appearance, 915

  Albumen, what is it, 899

  Alkalies, what are they, 36

  Amber, or electrum, what is it, 564

  Animals, how is their greater warmth in winter provided for, 168

  Animal forms, why are there so many, 1029

  Animal furs, why do they become thicker in the winter, 1035

  Animals, why have carnivorous, long pointed teeth, 1038


  LESSON IV.

  Animals with long necks, why have they large throats, 1049

  Animals, why cannot flesh-eaters live upon vegetables, 1071

  Animals, why can ruminating recover the food from their paunches, 1089

  Animals, why can ruminating keep the chewed from the unchewed food in
    their stomachs, 1090

  Animals, why do the smaller animals breed more abundantly than the
    larger ones, 1094

  Animals, domestic, why may change of weather be expected when they are
    restless, 1107

  Animals, plants, and minerals, what are the differences between them,
    1140

  Animals that graze, why do they crop the tender blades, but leave the
    tall grass, 1287


  LESSON V.

  Animals, distribution of, 1326

  Arms and hands, why do we see blue marks upon them, 896

  Arms and legs, why does it require the influence of the will to set
    them in motion, 917

  Arms and legs, why are they made subject to the will, 919

  Ascending, what is the cause of bodies, 775

  Atmosphere, how is it heated, 232

  Atmospheric humidity, why does it sometimes form clouds, at others form
    dews, fogs, mists, &c., 409

  Atmospheric pressure, how high will it raise water, 652

  Atmosphere, what is the, 639

  Atmosphere, to what height does it extend, 639

  Atmosphere, what is the amount of its pressure, 641

  Atmosphere, what is the proportion of watery vapour in the, 642

  Atmosphere, why are its upper regions intensely cold, 444

  Atmosphere, what is the greatest height ever reached in the, 648


  LESSON VI.

  Atmospheric pressure, what is the total amount on the earth's surface,
    644

  Atmosphere, what is the amount of its pressure upon the human body, 645

  Atmosphere, why do we not feel its pressure, 646

  Atmosphere, to what extent may its pressure vary, 702

  Attractive agent, what is an, 76

  Attraction, what is it, 772

  Attraction, how many kinds are there, 773

  Aurora Borealis, what is the cause of, 590


  Bananas or plantains, where are they cultivated, 1220

  Bark Peruvian, where is it produced, 1228

  Barometer, what is a, 691

  Barometer, why does it indicate the pressure of the atmosphere, 692

  Barometer, why is it also called a "weather-glass", 693

  Barometers, why are they constructed with circular dials, 694

  Barometer, why does the hand change its position when the mercury rises
    or falls, 695

  Barometer, why does tapping its face cause the hand to move, 696

  Barometer, why does its fall denote the approach of rain, 699


  LESSON VII.

  Barometer, why does its rise denote the approach of fine weather, 700

  Barometer, how does it enable us to calculate the height of the
    mountains, 701

  Barometer, when does it stand highest, 704

  Barometer, when does it stand lowest, 705

  Barometer, what effect has heat upon the, 707

  Barometer, what effect has cold upon the, 708

  Balloons, why do they ascend in air, 830

  Balloons, why do air balloons become inflated, 831

  Balloons, why do they sometimes burst when they reach a high altitude,
    832

  Bat and ball, what principles of natural philosophy are illustrated in
    the play, 867

  Bats, why have they hooked claws in their wings, 1079

  Bats, why do they fly by night, 1080


  LESSON VIII.

  Bats, why do they sleep during winter, 1081

  Beds, why should they be raised two feet from the ground, 15

  Bed-room windows, why are they sometimes covered with ice crystals, 344

  Beer, why will it not run out of a cask until a hole is made at the
    top, 660

  Beer, why does it get flat, 805

  Bees, why have they stings, 1101

  Bees, why may we expect fine weather when bees wander far from their
    hives, 1114

  Beetles, why are they called "coleoptera", 1319

  Beetles, why have they hard horny wing-cases, 1320

  Beetles, why have many of them hard horns, 1321

  Bile, why does it separate nutritious from innutritious matter, 884

  Birds, why have water-fowls feathers of a close and smooth
    texture, 1033

  Birds, why are they covered with feathers, 1030

  Birds, why does black down grow under their feathers on the approach of
    winter, 1036

  Birds, why have they hard beaks, 1040

  Birds, why are their beaks generally long and sharp, 1041

  Birds, why are their bones hollow, 1050

  Birds, why do they lay eggs, 1051


  LESSON IX.

  Birds, why have those with long legs short tails, 1052

  Birds, why have aquatic web-feet, 1059

  Birds, why have those that swim and dive short legs, 1060

  Birds, why have some deep rough notches on the under surfaces of their
    feet, 1061

  Birds, why have they gizzards, 1072

  Birds of prey, why have they no gizzards, 1084

  Birds, why may wet and thunder be expected when they cease to sing, 1121

  Birds of passage, why, if they arrive early, may severe weather be
    expected, 1121

  Birds, geological distribution of, 1326

  Birds, tameness of in unfrequented countries, 1327

  Birds, why are birds of song not also remarkable as birds of plumage,
    1328

  Birds, what are the velocities of their flights, 1329

  Birds, what is the cause of their migrations, 1330

  Black, why should parts of kettles and saucepans be allowed to remain,
    204

  Blood, in what proportions are the gases found in it, 39


  LESSON X.

  Blood, what is venous, 41

  Blood, what is arterial, 42

  Blood, what is the constitution of the, 899

  Blood, what quantity does the human body contain, 920

  Blood, how frequently does the whole quantity pass through the system,
    922

  Blowing upon tea, why does it cool it, 174

  Bow, why does it propel the arrow, 847

  Bow and arrow, what line does the arrow describe, 848

  Bow and arrow, what forces tend to arrest the arrow, 849

  Bow and arrow, why are there feathers at the ends of arrows, 850

  Bones, how many are there in the human body, 923

  Bones, of what substances are they composed, 924

  Bones, what are the uses of the, 925

  Bones, why are those of the back hollowed out, 927

  Bones, why are those of the skull arched, 930

  Bones, why are those of the skull divided by small sutures, 931

  Bones, why are they hollow, 934


  LESSON XII.

  Bones, why are those of the arms and legs formed into long shafts, 935

  Bones, why are those of the feet and hands numerous and small, 936

  Botanical geography, 1208

  Brain, why is it placed within the skull, 926

  Bread-fruit trees, where are they natives of, 1223

  Breathing, is it a kind of combustion, 17

  Breaths, have people ever been poisoned by their own, 24

  Breezes, why are summer said to be cool, 170

  Breezes, what is the cause of sea and land, 235

  Bubbles, why do they ascend in the air, 236

  Bubbles, why do they fall, after having ascended, 237

  Bubbles, why do they display rainbow colours, 499

  Bubbles, why are they round, 825

  Bubbles, why are they elongated when being blown, 826

  Bubbles, why do they close, and become perfect spheres when shaken from
    the pipe, 827

  Bubbles, why do they change their colours in the sunshine, 828

  Bubbles, why do they burst, 829


  LESSON XI.

  Burning or supporting combustion, what is the difference, 45

  Burning-glasses, why do they appear to set fire to substances, 80

  Butterflies, why do they lay their eggs upon cabbage-leaves, 1099

  Butterflies' eggs, why do they lie dormant in the winter, 1288

  Butterflies, why do they fly by day, 1296


  Calms, why do they prevail at the equator, 671

  Caloric, what is it, 72

  Caloric, what is the source of it, 73

  Caloric, what are the effects of it, 74

  Caloric, why is it called a repulsive agent, 75

  Caloric, how may it be excited to develope heat, 79

  Caloric, is there any in ice, snow, water, marble, &c., 89

  Caloric, how do we measure the quantity of in any substance, 329

  Caloric, how does it travel, 332

  Caloric, how do we know that it is caloric which fuses metals, 334

  Calves and lambs, why have they no horns, 1069

  Camel, why has its stomach a number of distinct bags, 1065

  Candles, why do tallow require snuffing, 264


  LESSON XIII.

  Candles, why do composite and wax not require snuffing, 265

  Candle, what becomes of it after it is burnt, 269

  Capillary blood-vessels, why are they found in every part of the
    system, 919

  Capillary attraction, what is it, 780

  Carbonic acid gas, how is it formed, 9

  Carbonic acid gas, what becomes of it, 10

  Carbonic acid gas, is it heavier or lighter than air, 11

  Carbonic acid gas, what are the chief sources of, 16

  Carbonic acid gas, what is its effect upon the human system, 21

  Carbonic acid gas, what becomes of that formed by combustion, 59

  Carbonic acid gas, what proportion is dangerous to life, 60

  Carbonic acid, what is it, 798

  Carbonic acid, where does it chiefly exist, 799

  Carbonic acid, what are its pure states, 800

  Carbon, what is it, 18

  Carbon, will it produce flame when burnt in oxygen, 106

  Carbon and hydrogen, what differences characterise the combustion of,
    268


  LESSON XIV.

  Carbon, what is the purest form of it, 277

  Card, why do the images on each side blend while a card is revolving,
    846

  Caterpillars, why do they appear in the spring, 1289

  Caterpillars, why do they eat voraciously, 1290

  Caterpillars, why do they pass into the state of the chrysalis, 1291

  Caterpillars, why do they become torpid in the chrysalis, 1292

  Caterpillars, why do they attach themselves to the leaves of plants
    when in the chrysalis, 1294

  Cats, &c., why do they see in the dark, 981

  Cats' eyes, why are the pupils of nearly closed by day, 982

  Cats, &c., why have they whiskers, 1096

  Cattle, why if they run round in meadows may thunder be expected, 1122

  Ceiling, how did Mr. Sands walk on the, 664

  Champagne, why does it effervesce, 806

  Champagne, why do bubbles rise from it in two or three columns, 807

  Charcoal, why is it dangerous to burn it in rooms, 20


  LESSON XV.

  Charcoal fires, why do they not give flames, 107

  Charcoal, what is it, 275

  Charcoal, why does it act as a disinfectant, 809

  Chicory, what is it, 1196

  Chimney, why does it cease smoking after the fire has been lighted a
    little while, 680

  Chimney, why does a long one create a better draught than a short one,
    681

  Chimneys, why do some smoke when windows and doors are closed, 683

  Chimneys that stand under elevated objects, why do they smoke, 685

  Chimneys, why do sooty smoke, 687

  Chimneys, why do they smoke in damp and gusty weather, 688

  Chimney, why does it smoke when first lighted, 679

  Chocolate, what is it, 1194

  Circulation, why are the venous blood and chyle sent to the lungs, 887

  Circulation, what is the course of the arterial blood, 888

  Circulation, why does the blood impart vitality, 891


  LESSON XVI.

  Circulation, how do we know the blood is alive, 892

  Circulation, why does the blood circulate, 893

  Circulation, how is the body renewed by the blood, 894

  Circulation, how does the blood return to the lungs after it has
    reached the extremities, 895

  Circulation, why are the veins more perceptible than the arteries, 897

  Circulation, why when we prick the flesh does it bleed, 893

  Circulation, what occurs during the, 899

  Circulation, what becomes of the matter collected by the blood, 901

  Circulation, how is the blood propelled through the arteries, 916

  Circulation, why are the capillary vessels capable of receiving the
    quantity of blood sent through larger vessels, 917

  Cinnamon, where is it produced, 1239

  Cleanliness, why does it promote health, 1015

  Clothes on fire, why should persons throw themselves down, 252

  Clothing, why do some articles feel cold, and others warm, 120


  LESSON XVII.

  Clothing, are conductors or non-conductors the warmer, 121

  Clothing, why are white and light-coloured articles cool, 218

  Clothing, why are dark-coloured dresses worn in winter, and light in
    summer, 230

  Clouds, what are they, 373

  Clouds, why do we not see them ascend, 375

  Clouds, why are they invisible when they rise, but become visible when
    they have ascended, 376

  Clouds, why do they not descend to the earth, 377

  Clouds, at what altitudes do they fly, 378

  Clouds, how many descriptions are there, 379

  Clouds, what produces their various shapes, 380

  Clouds, what are their dimensions, 381

  Clouds, how are they affected by winds, 382

  Clouds, what do Cirrus foretell, 389

  Clouds, what do Cumulus foretell, 390

  Clouds, what do Stratus foretell, 391

  Clouds, what do Nimbus foretell, 392

  Clouds, what do Cirro-cumulus foretell, 393

  Clouds, what do Cirro-stratus foretell, 394

  Clouds, what do Cumulo-stratus foretell, 395


  LESSON XVIII.

  Clouds, why are cloudy days colder than sunny days, 396

  Clouds, why are cloudy nights warmer than clear nights, 397

  Cloudy days and nights, why are they not always wet, 432

  Clouds, why are they white, 531

  Clouds, why are they sometimes yellow, 533

  Clouds, what develops the electricity in the, 581

  Clouds, why do they sometimes move towards each other from opposite
    directions, 778

  Clouds, why do they gather around mountain tops, 781

  Cloves, where are they produced, 1231

  Coal, what is it, 271

  Coal, why do we know that it is of vegetable origin, 273

  Coal, what are the chemical components of, 274

  Coals, why do they produce yellow flame, 279

  Cockles, why have they stiff muscular tongues, 1087

  Cocoa, what is it, 1195

  Cocoa, what tree produces it, 1221

  Coffee-pot, why has it a wooden handle, 125


  LESSON XIX.

  Coffee, what is it, 1193

  Coffee, where is it cultivated, 1224

  Cohesion, what is the attraction of, 776

  Coke-fires, why do they not give flames, 107

  Coke, what is it, 278

  Cold, when is a body said to be, 78

  Cold, what is the cause of the sensation, 133

  Cold, does it radiate, 207

  Colour, why is a substance white, 466

  Colour, why is a substance black, 467

  Colour, why is a rose red, 468

  Colour, why is a lily white, 469

  Colour, why is a primrose yellow, 470

  Colour, why are there so many varieties of colour and tint in nature,
    471

  Colours, remarks upon, 501

  Combustion, what takes place during, 48

  Combustion, how many kinds are there, 93

  Conductors of heat, what substances are good, 110

  Conductors of heat, why do bad conductors readily ignite, 295

  Combustion, what is spontaneous, 311

  Combustibles used for lighting, which vitiates the air most, 62

  Conduction of heat, what is the, 113

  Convection, what is the chief effect of the law of, 243


  LESSON XX.

  Cork, what is it, 1271

  Cork-tree, why does it shed its own bark, 1272

  Corns, why when they ache may rain be expected, 1115

  Corn, why does the young ear come up enfolded in two leaves, 1167

  Cotton, what is it, 1199

  Cough, why do we, 1023

  Crickets, why do they make a chirping noise, 1123

  Cross-bills, why do their mandibles overlap each other, 1136

  Cup in a pie, why does it become filled with juice, 631

  Cup in a pie, does it prevent the juice from boiling over, 662


  Dates, what are they produced by, 1221

  Death-watch, why does it make a ticking noise, 1301

  Dew, what is it, 345

  Dew, what causes the decline of temperature which produces it, 347

  Dew, why is there little or none, when the nights are cloudy, 348

  Dew, why does it form most abundantly on cloudless nights, 349

  Dew, why is there little under the branches of thick foliage, 351


  LESSON XXI.

  Dew, why is there none formed on windy nights, 352

  Dew, why are valleys and low places chiefly subject to it, 353

  Dew, what bodies receive little of it, 355

  Dew, what bodies receive most of it, 354

  Dew, at what period of the night is it chiefly formed, 356

  Dew, why is it chiefly formed at that period, 357

  Dew, in what parts of the world is the greatest quantity formed, 358

  Dew, in what parts of the world is the least quantity formed, 359

  Dew, why is it seldom formed at sea, 360

  Dew, why is it, when heavy, regarded as a precursor of rain, 361

  Dew, what is honey-dew, 364

  Dew, why does it lie on the exposed sides of screens of plants, 401

  Dew, why does it rest upon the upper surfaces of leaves, 402

  Dews, why are cultivated lands more subject to them than those that are
    uncultivated, 403


  LESSON XXII.

  Dew, why does the gravel-walk receive less dew than the grass, 404

  Dew, why does little of it form at the base of hedges, walls, and
    trees, 406

  Dews, why do morning dews and mists usually come together, 407

  Dew, what effect have winds upon its formation, 408

  Dew, why does it form in round drops upon leaves, 794

  Diamond, what causes the brilliant colours of the, 501

  Digestion, why does food flow more freely to the stomach during, 879

  Digestion, why does excess in eating impair, 880

  Digestion, what changes occur to food in the stomach, 881

  Digestion, what causes bilious attacks, 882

  Digestion, how is the nutritious matter taken from that which is
    innutritious, 885

  Digestion, what becomes of the nutrition when it enters into the
    circulation, 886

  Dish-covers, why should they be plain in form, and have bright
    surfaces, 203

  Dogs, geographical distribution of, 1333

  Dream, why do we, 1020

  Drowsiness, why is it felt in crowded rooms, 22


  LESSON XXIII.

  Ducks and geese, why do they dash water over their backs on the
    approach of rain, 1105

  Ducks and geese, why have they square-pointed bills, 1044

  Dyes, vegetable, what are they, 1259


  Ear, why is it spread out externally, 984

  Ears, why do hairs grow across them, 986

  Ear-wig, why is it so called, 986

  Ears, why is wax secreted in the, 987

  Ears, why do singing noises occur in the, 988

  Ears, why do people become deaf, 989

  Ears, why do people accustomed to loud noises feel no inconvenience
    from them, 990

  Ears of animals of prey, why do they bend forward, 1063

  Ears of animals of flight, why do they bend backward, 1064

  Earth, why is it warmer than air during sunshine, 398

  Earth, why is it colder than air after sunset, 399


  LESSON XXIV.

  Earth, how can man weigh the, 784

  Earth, what is the weight of the, 788

  Earth-worms, why have they no feet, 1085

  Echoes, why do some occur immediately after the sounds, 742

  Echoes, why do some occur at a considerable interval after the sound,
    743

  Echoes, why do some change the tone and quantity of sounds, 744

  Echoes, why are there sometimes several to one sound, 745

  Echoes, are they caused only by distant objects, 746

  Echoes, what are they, 741

  Electricity, what is it, 561

  Electricity, why is it so called, 562

  Electric fluid, why is it so called, 566

  Electrics, what substances are, 567

  Electricity, what is positive, 568

  Electricity, what is negative, 569

  Electricity, what is vitreous, 570

  Electricity, what is resinous, 570

  Electrical phenomena, what produces them, 571

  Electricity, how does its equilibrium become disturbed, 572

  Electricity, how does it seek to regain its equilibrium, 573

  Electricity, what substances are conductors, 574

  Electricity, what substances are non-conductors, 575

  Electricity, what substances are insulators, 576


  LESSON XXV.

  Electricity, what is the effect when a current of electricity meets
    with an insulator, 577

  Electric sparks, what is the cause of, 578

  Electricity, why does lightning attend it, 584

  Electricity, why does it affect the shape of clouds, 613

  Electric storms, why are they more frequent in hot than in cold
    weather, 624

  Electric storms, why do they frequently occur after dry weather, 625

  Electric storms, why do they purify the air, 629

  Electricity, what is Voltaic, 636

  Electrical attraction, what is it, 778

  Elementary body, what is meant by, 19

  Element, what is the most abundant in nature, 756

  Elephant, why has it a short unbending neck, 1076

  Elephant, why has it a trunk, 1077

  Elephants' hind legs, why do they bend forward, 1078

  Etna, what are the botanical regions of Mount, 1240

  Endogenous stems, what are they, 1280


  LESSON XXVI.

  Endogenous stems, why do they abound in tropical climates, 1281

  Endogenous stems, why have they no bark, 1282

  Endogenous stems, why do they grow to a great height, 1283

  Exogenous stems, what are they, 1279

  Exercise, why does it promote health, 1016

  Exercise, why does it make us feel warm, 839

  Explosions of gas, what is the best method of preventing, 65

  Eye-balls, why are they white, 911

  Eye-balls, why do they sometimes become blood-shot, 912

  Eyes, why are they placed in the sockets of the skull, 929

  Eyes, why are we able to move them, 965

  Eye, why does the pupil look black, 968

  Eye, why is the pupil larger sometimes than at others, 969

  Eyes, why have we two, 970

  Eyes, why having two, do we see singly, 971

  Eyes, why are they provided with eyelids, 972

  Eyelids, why are they fringed with eyelashes, 973

  Eyes, whence are their humours derived, 976


  LESSON XXVII.

  Eyes, why do we feel inconvenienced by sudden light, 978

  Eyes, why if we look upon a bright object and turn away, are we unable
    to see, 979

  Eyes, why are we able to see better after a little while, 980

  Eyes, why do cats, bats, owls, &c., see in the dark, 981

  Eels, why are their eyes covered with a transparent horny coat, 1130


  Falling, what is the cause of bodies, 774

  Fanning the face, why does it make us feel cooler, 172

  Fata morgana, what is the cause of, 527

  Fatigue, why do we feel, 1017

  Feather, why does it fall to the earth more gradually than a shilling,
    791

  Features, why do we preserve the same through life, 903

  Feel, why do we, 1004

  Feeling, why is it impaired when the hands are cold, 1006

  Feeling, why do the fingers prick and sting when they again become
    warm, 1007


  LESSON XXVIII.

  Feeling, why do persons whose legs or arms have been amputated, for
    some time continue to feel the part that has been removed, 1008

  Fibrin, what is it, 899

  Fingers, why can we raise them, 943

  Fingers, why can we draw them back after they have been raised, 944

  Fire, why does it burn more brightly when blown by a bellows, 27

  Fire, what is it, 82

  Fire, what are its properties, 83

  Fire, what elements take part in its maintenance, 84

  Fire, how does its combustion begin, 85

  Fire-screens, how do they contribute to keep rooms cool, 217

  Fire, why is it sometimes put out by blowing it when it is low, 262

  Fire, why does poking it cause it to burn more brightly, 287

  Fires, why do "blowers" improve the draft of air, 288

  Fire, why does it sometimes appear red, and without flame, 283

  Fire, what effect has it upon air, 284

  Fires, why do charcoal and coke burn without flame, 292

  Fires, why are charcoal and coke difficult to light, 293

  Fires, a new plan of kindling, 293


  LESSON XXIX.

  Fires, why in lighting them do we first lay in paper, wood, and coal,
    298

  Fire, why does a poker laid across the top revive it when dull, 302

  Fire-places, why should they be near the ground, 303

  Fire, why does the blacksmith sprinkle water upon the coals of his
    forge, 308

  Fires, what is the best method of conveying air to, 684

  Fish, why does putrifying look luminous, 95

  Fishes, why have they fins, 1053

  Fishes, why are their fins proportionately so much smaller than the
    wings of birds, 1054

  Fishes, why have they scales, 1055

  Fishes, why do they float in streams, with their heads towards the
    current, 1056

  Fishes, why have they air-bladders, 1057

  Fishes, why do not their eyes contract, 1129

  Fishes, why have they no eyelids, 1132

  Fishes, why have they the power of giving their eye-balls a sudden
    motion, 1133

  Fishes, why are their tails so much larger than their fins, 1137

  Flame, what is it, 96


  LESSON XXX.

  Flame, what temperature is required to produce it, 101

  Flame of a candle, why does the lower part of the flame appear blue, 246

  Flame of a candle, why does the middle of the flame look dark, 217

  Flame of a candle, why does the upper part produce a bright yellow
    light, 248

  Flame of a candle, why is there a fringe of pale light around the
    flame, 249

  Flame of a candle, why does it terminate in a point, 250

  Flame of a candle, why does it lengthen when anything is held over it,
    251

  Flame or spark, why does pressing it put it out, 253

  Flame of a candle, why does holding a candle upside down put it out, 257

  Flame of a candle, why is it more difficult to blow out the flame of a
    candle with a cotton wick than one with a rush wick, 258

  Flame of a candle, why does blowing sharply on it put it out, 259

  Flame of a candle, why will a gentle puff of air sometimes relight it,
    260


  LESSON XXXI.

  Flame of a candle, why will not a similar puff rekindle a rushlight, 261

  Flame of a candle, why will a piece of paper twisted to form an
    extinguisher put it out, 263

  Flame of a candle, why does it become dim when the wick is loaded with
    carbon, 267

  Flames of a fire, why do some appear much whiter than others, 280

  Flames of a fire, why do some of them appear blue, 282

  Flesh, why does it heal when we cut it, 902

  Flesh-eaters, why do they satisfy themselves with a rapid meal, 1092

  Flesh, why do the marks of deep cuts remain, 905

  Flesh, why does that under the nails look red, 907

  Flies, how can they walk on the ceiling, 663

  Flies, why have they fine hairs growing on the extremities of their
    legs, 1102

  Flowers, what is the chief cause of the differences of their
    temperatures, 227

  Flowers, why may wet weather be expected when their perfume is strong,
    1103


  LESSON XXXII.

  Flowers, why, if certain close, may rain be expected, 1116

  Flying-top, why does it rise on the air, 843

  Flying-top, why does it return to the earth, when its rotations are
    expended, 844

  Focus, what is a, 81

  Fogs, what are they, 365

  Fogs, why are certain coasts very liable to them, 366

  Fogs, what are dry, 367

  Fogs, why do they frequently rise in the morning and fall in the
    evening, 371

  Fogs, why do they sometimes rest upon a locality for days together, and
    then disappear, 372

  Food, why do we eat it, 869

  Food, why do we eat animal and vegetable, 172

  Food, why do we masticate it, 871

  Food, how does it descend into the stomach, 875

  Food, why do we not feel it being transmitted through the throat, 876

  Food, why do we feel uneasy after eating to excess, 877

  Food, why do we feel drowsy after eating heartily, 878

  Food, why do some portions nourish us, while other portions are
    useless, 883


  LESSON XXXIII.

  Fossil, vegetable, what is it, 272

  Friction, why does it produce heat, 321

  Friction, why does rubbing two surfaces together attract latent heat,
    322

  Frost, why is the air warmer during, 163

  Frost, what is white, 412

  Frost, what is black, 413

  Frost, why are black frosts said to last, 414

  Fruit, why do gooseberries, plums, &c., taste acid, 1184

  Fruit, why do ripe taste sweet, and unripe sour, 1185

  Fruits, why are succulent most abundant in tropical climates, 1207

  Fruits and vegetables, why do they ripen in succession, 1284

  Furs, why are they worn in winter, 166


  Galvanism, what is it, 635

  Gas, what kind lights our streets, 56

  Gas, why does it expand in thin air, 833

  Geology, what has been its influence upon botanical geography, 1249

  Giraffes, why have they small heads, 1322

  Giraffes, why have they long necks, 1323

  Giraffes, why have they long and flexible tongues, 1324


  LESSON XXXIV.

  Giraffes, why are their nostrils narrow and small, and studded with
    hairs, 1325

  Glass upon a lamp, why does it increase the brilliancy of the light, 266

  Glass, why is it transparent, 506

  Glass, does transparent reflect any light, 507

  Glow-worms, why have they brushes attached to their tails, 1127

  Glow-worms, why do they emit light, 1128

  Gnats, why are their larvæ and pupæ found in water, 1314

  Gnats, why may fine weather be expected if they fly in large numbers,
    1110

  Grasses, why are they so widely diffused throughout nature, 1166

  Grasshoppers, why are they comparatively active in their pupa stages,
    1293

  Gravitation, what is the attraction of, 774

  Guano, why is it a good manure, 1262

  Gum resins, what are they, 1255

  Gums, vegetable, what are they, 1254

  Gunpowder, why does it explode, 808

  Gutta-percha, whence is it obtained, 1254


  LESSON XXXV.

  Hail, what is it, 448

  Hail, why is it supposed that the electrical state of the clouds
    affects the formation of hail, 449

  Hail-storms, why do they usually occur by day, 450

  Hairs, why do they grow across the passages of the nostrils, 993

  Halo, what is a, 494

  Halo, what is the cause of a, 495

  Haloes, why are they sometimes large, and at other times small, 496

  Haloes, why do they foretell wet weather, 497

  Hands, why when we hold them against the candle do we perceive a
    crimson colour, 906

  Hay-stacks, why do they sometimes take fire spontaneously, 316

  Head, why is it set upon the neck, 928

  Hearing, why do people engaged in battle frequently lose their, 991

  Hearing, death of a dog through noise, 991

  Heart, why does it beat without any effort of the will, 948

  Heart, why is it placed in the chest of the body, 932

  Heart and lungs, why are they enclosed by ribs, 933

  Heart, why are its motions made independent of the will, 950


  LESSON XXXVI.

  Heat, what is it, 71

  Heat, what are the properties of, 86

  Heat, what is animal, 87

  Heat, what is latent, 88

  Heat, what is a conductor of, 108

  Heat, what is a non-conductor of, 109

  Heat, how is it transmitted from one body to another, 119

  Heat, what is the radiation of, 114

  Heat, what is the reflection of, 115

  Heat, what is the absorption of,116

  Heat, what is the convection of, 117

  Heat, what is the cause of the sensation, 134

  Heat, what becomes of that which the hearth-stone receives, 136

  Heat, how long does a substance feel hot or cold to the touch, 139

  Hearth-rug, and hearth-stone, their relative states of heat, 142

  Heat, which are the better conductors, fluids or solids, 146

  Heat, why are dense substances the best conductors, 147

  Heat, why are fluids bad conductors, 148

  Heat, why are woollen fabrics bad conductors, 149

  Heat, is air a good or bad conductor, 150


  LESSON XXXVII.

  Heat, is water a good or a bad conductor, 151

  Heat, how do we know that air is not a good conductor, 155

  Heat, how do we know that water is not a good conductor, 156

  Heat, why are bottles of hot water wrapped in flannel, 158

  Heat, why are hot rolls wrapped in flannel, 159

  Heat, what is the highest degree that man can bear, 176

  Heat, why may man endure a high degree without injury, 178

  Heat, why may we believe that the internal heat of the earth does not
    arise from terrestrious combustion, 224

  Heat, what is the radiation of, 181

  Heat, what becomes of that which is radiated, 186

  Heat, when does a body radiate it, 184

  Heat, does the movement of the air affect the radiation of, 188

  Heat, why will not the motion of air disturb the rays of, 190

  Heat, what bodies are good radiators of, 192

  Heat, what bodies are bad radiators of, 193

  Heat, why does water keep hot longer in a bright metal jug, 195


  LESSON XXXVIII.

  Heat, may it be reflected, 210

  Heat, are light or dark-coloured bodies the best reflectors, 211

  Heat what bodies are the best reflectors of, 212

  Heat, why is that which is reflected less intense than the primary, 214

  Heat, can it be reflected in any great intensity, 215

  Heat, are good reflectors also good absorbers, 216

  Heat of the sun's rays, how is it diffused, 219

  Heat, how do we know that it is absorbed by the earth, 222

  Heat, do plants absorb it, 225

  Heat, how is it diffused through the atmosphere, 232

  Heat, how is it diffused through the ocean, 233

  Heat, why is it developed during chemical changes, 312

  Heat, what are the sources of, 323

  Heat, what is the accepted theory of, 328

  Heat, what is the point at which it becomes luminous, 545

  Heat, what is the relative intensity of primary and reflected, 548

  Heat to cold, why does a sudden change bring on illness, 1013


  LESSON XXXIX.

  Heat of the earth, Humboldt's opinion upon the internal, 1335

  Heat of the earth, Hunt's opinion upon the internal, 1336

  Hear, why do we, 983

  Hiccough, why do we, 1027

  Hoar-frost, what is it, 362

  Hoar-frost, why does it foretell rain, 363

  Hoar-frosts, why are they so frequent, and black-frost so unfrequent,
    412

  Hogs, why have Indian large tusks turning back towards their eyes, 1068

  Hog, why is the under-jaw of the, shorter than the upper-jaw, 1039

  Hoop, why does it roll without falling to the ground, 861

  Hoop, why does it when falling make several side revolutions, 862

  Horses, why have they smaller stomachs proportionately than other
    animals, 1097

  Horse, why has it no gall-bladder, 1098

  Horses, why is the secretion of their eyes thick and glutinous, 1134

  Horses and cattle, why do they stretch out their necks, and snuff the
    air on the approach of rain, 1106

  Horse-chestnut, why is it unfit for food, 1203

  Hot, when is a body said to be, 77


  LESSON XL.

  Hot water, why does it feel hotter in a metal jug than in an
    earthenware one, 126

  Hot metal, why does it feel hotter than hot wool, 130

  Hot metal and hot wool, which would become cold first, 131

  Hot and cold bodies, why, when placed near each other, do their
    temperatures approximate, 331

  Humming-tops, why do we see the figures painted on them before they
    spin, but not while they are spinning, 813

  Humming-top, why does it make a noise, 810

  Hydrogen, what is it, 49

  Hydrogen, will it support animal life, 50

  Hydrogen, will it support combustion, 51

  Hydrogen, why will it explode, 52

  Hydrogen, where does it chiefly exist, 54

  Hydrogen, how is it obtained from coal, 57

  Hydrogen-gas, is an escape of it dangerous to life, 63

  Hydrogen-gas, what proportion mixed with air will explode, 64

  Hydrogen-gas, does it rise or fall, 66


  LESSON XLI.

  Hydrogen-gas, what proportion is dangerous if inhaled, 67

  Hydrogen-gas, what proportion may be recognised by its smell, 68

  Hydrogen-gas, may the use of it be considered dangerous, 70

  Hydrogen-gas, what sources of it are there in our dwellings, 69

  Hydrogen, why will it burst into flame when coals become heated, 100

  Hydrogen, why does hi-carburetted burn with a whiter flame than common
    coal-gas, 281


  Ice, why are blocks of it wrapped in flannel in summer time, 154

  Ice, why does it melt, 325

  Ice, why does it occupy more space than water, 752

  Ignis fatuus, what is it, 318

  Incidence, what is the line of, 519

  Incidence, what is the angle of, 521

  India-rubber, where is it obtained, 1254

  Infants, why have they no teeth, 1070

  Insects, why have they a large number of eyes, 1083

  Insects, why have they long projections from their heads, 1100

  Insects, why do they attach their eggs to leaves, 1295

  Insects, why do they multiply so numerously, 1300


  LESSON XLII.

  Insects, what is a larva, 1302

  Insects, what is a pupa, 1303

  Insects, what is a chrysalis, 1304

  Insects, what is a nymph, 1305

  Insects, why do they abound in decaying substances and in putrid
    waters, 1313

  Insects, why do we see them in tanks of rain-water, 1314

  Iron articles, why are they intensely cold in winter, 132

  Iron articles, why do they usually feel cool, even when near a fire, 132

  Ironing-box, why does the iron sometimes become too large for the box
    to receive it, 335

  Ironing-box, why does the iron enter it, when partially cooled, 336

  Iron, why does it rust when wetted, 768


  Jew's-harps, why do they give musical sounds, 851

  Jew's-harps, why will they not produce loud sounds unless they are
    applied to the mouth, 852

  Jew's-harps, why does the alteration of the form of the mouth alter the
    sounds, 853


  Kangaroos and opossums, why have they pouches in which they carry their
    young, 1139


  LESSON XLIII.

  Kettle-holders, of what use are they, 128

  Kettles and saucepans, why should the lids and fronts of be kept
    bright, 206

  Kettles, why do they become encrusted with stony deposits, 762

  Kite, why does it rise in the air, 840

  Kite-string, why does it feel hot when running through the hand, 841

  Kite, why does running with it cause it to ascend, 812

  Knowledge, why should we seek it, 1

  Knowledge, why does the possession of it give us power, 2

  Knowledge, what are the benefits of, 3


  Latent heat, will the abstraction of it reduce the bulk of bodies, 337

  Latent heat, how do we know that it exists in air, 339

  Laugh, why do we, 1026

  Ligaments, what are they, 937

  Ligaments, why are they wrapped around the joints, 938

  Light, what is it, 451

  Leaves, why are they green, 1181

  Leaves, why do some turn yellow, 1186

  Leaves, why do they fall off in the autumn, 1187

  Leaves, how to make skeleton, 1159


  LESSON XLIV.

  Leaves, why do they turn brown in autumn, 1183

  Legs crossed, why do we see the elevated leg move at regular intervals,
    918

  Light, at what velocity does it travel, 453

  Light, how long does it take to travel from the sun to the earth, 454

  Light what are the minor sources of, 457

  Light, what is a ray of, 458

  Light, what is a medium of, 459

  Light, what is a beam of, 460

  Light, what is a pencil of, 461

  Light, what is the radiant point, 462

  Light, what is the focus of, 463

  Light, what is the constitution of a ray of, 464

  Light, why are its rays white, 465

  Light, what are the estimated vibrations of, 465

  Light, what is the refraction of, 472

  Light, is it refracted when it falls upon a surface in a straight line,
    473

  Light, is the direction in which its rays are best dependent on the
    densities of the media, 474

  Light, why does a spoon look bent when placed in a basin of water, 477

  Light, why do we see the rays of the sun burst through the clouds in
    different directions, 478


  LESSON XLV.

  Light, why is the apparent depth of water always deceptive, 479

  Light, why are some substances opaque to it, 511

  Light, how do we know that bodies reflect it in every direction, 517

  Light, meditation on, 517

  Light and heat, what are the differences between, 540

  Light and heat, are they combined in the sun's rays, 541

  Light and heat, how do we know that they are separate elements, 542

  Light and heat, in what respects are they similar, 543

  Light and heat, in what respects are they dissimilar, 544

  Light, what is polarized, 549

  Light, what is the velocity of artificial, 546

  Light, at what rate does the light of the stars travel, 547

  Light, why does it tarnish silver, 553

  Light, why does it affect colours, 554

  Light, why can pictures be taken by the sun's rays, 555

  Light, when does it scorch plants, 558

  Lightning, what is the cause of, 580

  Lightning, why does it sometimes become zigzag, 586

  Lightning, why is it sometimes forked, 587


  LESSON XLVI.

  Lightning, why is it sometimes like a lurid sheet, 588

  Lightning, when is the flash straight, 587

  Lightning, when does the flash appear blue, 591

  Lightning, why is it sometimes red, at others blue, yellow, or white,
  592

  Lightning, does it ever pass from the earth to the clouds, 593

  Lightning, does it pass from the clouds to the earth, 594

  Lightning, what is the force of, 595

  Lightning, why is it dangerous to stand near a tree during a storm, 596

  Lightning, why is it dangerous to sit near a fire during a storm, 598

  Lightning, why is it dangerous to be near water during a storm, 599

  Lightning, are iron houses dangerous, 600

  Lightning, why does it seize upon bell wires, &c., 601

  Lightning, are umbrellas with steel frames dangerous, 603

  Lightning, are iron bedsteads dangerous, 604

  Lightning, what is the safest situation during a storm, 606

  Lightning-conductors, do they attract electricity, 608


  LESSON XLVII.

  Lightning-conductors, which is the best metal for, 610

  Lightning-conductors, why have they sometimes been found ineffective,
    609

  Lightning-conductors, why should large buildings have several, 611

  Lightning-conductors, why should they have several branches penetrating
    the earth, 612

  Lightning, through what distance will its light penetrate, 622

  Lightning, how may we calculate the distance of a storm, 623

  Lightning, why is the flash generally succeeded by heavy rain, 626

  Lightning, why is a flash generally followed by a gust of wind, 627

  Lime-kilns, why do persons viewed through the hot air of, appear
   distorted and tremulous, 483

  Limpets, why is it difficult to strike them from rocks, 665

  Lips, why are they red, 913

  Liver, what effect has it upon the circulation, 901

  Looking-glass, why, if you hold one at an angle towards the sun, will
    light be thrown in an opposite direction, 208

  Loss, is there any such thing in the operations of nature, 270


  LESSON XLVIII.

  Lungs, why are they placed in the chest of the body, 932


  Magnetism, what is it, 633

  Magnetic bodies, what are they, 634

  Magpie, why is a single one said to foretell bad weather, 1118

  Mahogany, what is it, 1190

  Mahogany and other woods, why are there curious markings in, 1273

  Man, why is he born without a covering, 1034

  Man, why has he no external appendage to his mouth, 1037

  Marbles, why do they revolve when propelled along the ground, 818

  Marbles, why do striped appear to have more stripes when they are
    rolling than when at rest, 819

  Marbles, why do they rebound when dropped upon the pavement, 820

  Marbles, why do they roll furthest upon smooth surfaces, 821

  Marbles, how many forces contribute to stop their rolling, 882

  Marbles, why do the stripes upon them disappear when they are spinning
    rapidly, 823

  Marbles, why are the rings upon them most perceptible at the "poles,"
    while they are spinning, 824

  LESSON XLIX.
  Matches, do they ignite spontaneously, 313

  Meat, why is it sooner cooked when a tin screen is placed before the
    fire, 213

  Metal, why does it run like a fluid when melted, 333

  Mirrors, why do we see our features therein, 209

  Mirrors, why do we see our faces in them, 512

  Mirrors, what has the glass of to do with the reflection, 514

  Mirrors, why do compound mirrors reflect many images of one object, 515

  Mirrors, why do reflections appear as far behind a mirror as the object
    reflected stands before it, 518

  Mirage, what is the cause of the, 527

  Mists, what are they, 368

  Mists and fogs, what is the difference between them, 369

  Mists end fogs, why do they disappear at sunrise, 370

  Mistletoe, why have its berries a thick viscid juice, 1177

  Mistletoe, how are its seeds conveyed to the bark of trees, 1178

  Moles, why have they hard flat feet, 1074

  Mole's fur, why is it glossy and smooth, 1075


  LESSON L.

  Moles, why are they permanent, 904

  Moles, why may rain be expected when they throw up their hills, 1117

  Monsoons, what are they, 672

  Monsoons, what is the cause of, 673

  Mornings, why are they usually clear when frosty, 410

  Mother-of-pearl, what causes the rich tints displayed by, 500

  Moths, why do they fly by night, 1297

  Moths, why are their bodies generally covered with thick down, 1228

  Moths, why do they fly against the candle-flame, 1299

  Muscles, how many are there in the human body, 941

  Muscle, what is the constitution of a, 942

  Muscles, what degree of strength do they possess, 945

  Muscles, what is the stimulus which sets them in action, 946

  Mussels, why have they tendinous cords proceeding from their shells,
    1086


  Natural phenomena, a world of miniature, 690

  Nails, why have we got them at the fingers' ends, 908

  Nails, why is there a circular line of whitish colour at the root of
    the, 909


  LESSON LI.

  Nails, why do white spots occur upon the, 916

  Needle, why will it float if laid carefully upon water, 795

  Nerves, what are they, 951

  Nervous system, of what does it consist, 955

  Nerve, what is the constitution of a, 956

  Nervous fluid, what is the, 957

  Nerves, how many kinds are there, 958

  Nerves of motion, what are they, 959

  Nerves of sensation, what are they, 960

  Nerves of special sense, what are, 961

  Nerves of sympathy, what are the, 962

  Nights, why are they usually cold when clear, 411

  Nitrogen, what is it, 33

  Nitrogen, where is it found, 34

  Nitrogen, could animals live in it, 37

  Nitrogen, is it taken into the blood from the air, 40

  Nitrogen, will it burn, 44

  Nitrogen, what becomes of that which is inhaled, 46

  Nitrogen, where does it find a fresh supply of oxygen, 47

  Nitrous oxide, why does it excite the system, 38

  Non-conductors of heat, what substances are, 111

  Nostrils, why are they directed downwards, 994


  LESSON LII.

  Nose, why is it placed over the mouth, 995

  Nutmegs, where are they produced, 1232


  Ocean, how is it heated, 233

  Oils and fats, what are vegetable, 1204

  Oils and fats, animal, why are they found most abundantly in cold
    climates, 1205

  Oils and fats, vegetable, why are they found most abundantly in hot
    countries, 1206

  Opium, what is it, 1258

  Ostriches, why have they small wings, 1031

  Ostriches, why are their feathers soft and downy, 1032

  Otters, seals, &c., why have they web-feet, 1062

  Owls, why does their screeching denote change of weather, 1111

  Owls, why does their moping foretell death, 1112

  Oxen, sheep, deer, &c., why do they ruminate, 1088

  Oxen, and other quadrupeds, why have they a tough elastic ligament in
    their necks, 1138

  Oxygen, why is it necessary to life, 5

  Oxygen, what is its union with carbon called, 7


  LESSON LIII.

  Oxygen, what is it, 25

  Oxygen of the air, why does it not take fire, 28

  Oxygen, why do we know that it will not burn of itself, 29

  Oxygen, why do we know that it is necessary to our existence, 30

  Oxygen, where is it found, 31

  Oxygen, why is it mixed with nitrogen in the air, 32

  Oxygen of water, why does it not support fire, 307

  Oxygen, in what way does man use it, 757

  Ozone, what is it, 630

  Ozone, why do we know that electricity produces it, 631

  Ozone, what are the properties of, 632


  Paleness, what is the cause of, 914

  Palms, what are their characteristics, 1221

  Paper held over a candle-flame, why does it become scorched, 244

  Paper held below a candle-flame, why does it scarcely become warm, 245

  Paper, why does it more readily ignite than wood, 294

  Paper, why, if it is laid flat upon the fire, will it "char" before it
    ignites, 304


  LESSON LIV.

  Paper on a fire, why will it ignite when you send a puff of air to it,
    305

  Parachutes, why do they fall gradually to the ground, 834

  Parrots, &c., why have they crooked bills, 1047

  Parrots, why can they move their upper as well as their lower beak, 1048

  Particles of matter, why do they draw near each other, 776

  Particles of matter, why will they attach themselves to sealing-wax
    excited by friction, 779

  Pea and pin, why do they rotate upon a jet of air blown through a
    tobacco-pipe, 845

  Peg-top, why does it make less noise than a humming-top, 811

  Peg-top, why does it sometimes hum, and at other times not, 812

  Pelican, why has it a large pouch under its bill, 1093

  Pepper, where is it produced, 1229

  Perspiration, why does it cool the body, 173

  Perspire, why do we, 1009

  Perspiration, how is it formed, 1010

  Perspiration, what is insensible, 1011

  Perspiration, what is sensible, 1012


  LESSON LV.

  Phosphorous, why does it look luminous, 94

  Phosphorous, does it ignite spontaneously when placed upon a hot
    surface, 314

  Phosphorous, why does it ignite when sprinkled with powdered charcoal,
    315

  Photographic pictures, how does light produce them, 556

  Photographic rooms, why are they glazed with blue glass, 557

  Pith-tumblers, why do they always pitch on one end, 868

  Planets, how can man weigh them, 785

  Planets, how can man measure their distances, 786

  Plants, do they absorb heat, 225

  Plants, how do we know that they absorb heat, 226

  Plants, why do screens prevent frost from killing them, 400

  Plants, why, if we cut across their stems, do we see tubes arranged in
   parallel lines, 1159

  Plants, why do some droop and turn to the earth after sunset, 1167

  Plants, why are the seeds of many enclosed in rich juice or pulp, 1172

  Plants, why have some tough curly tendrils, 1173


  LESSON LVI.

  Plants, why have peas tendrils, and beans none, 1174

  Plants, why have grasses, &c., joints or knots in their stalks, 1176

  Plants, what is the circulation of sap in, 1179

  Plants, why does their sap ascend and descend, 1180

  Plants, why do they suffer from the smoke of cities, 1188

  Plants, why is it understood that some of them feel, 1141

  Plants, why is it understood that some of them move, 1142

  Plants, of what elementary substances are they composed, 1143

  Plants, whence do they derive their elementary substances, 1144

  Plants, how do they obtain carbon, 1145

  Plants, how do they obtain oxygen, 1146

  Plants, their decomposition of gases by day and by night, 1147

  Plants, how do they obtain hydrogen, 1147

  Plants, how do they obtain nitrogen, 1148

  Plants, how do they apply their elements to the formation of their
    structures, 1149

  Plants, how is their nutritive sap applied to their growth and
    nourishment, 1150


  LESSON LVII.

  Plants, why do they grow, 1154

  Plants, why if we break the stem of a hyacinth do we see a glutinous
    fluid exude, 1155

  Plants, why if we split the petal of a tulip do we see cells containing
    different colouring matters, 1156

  Plants, why if we break a pea-shell across do we find a transparent
    membrane, 1157

  Plants, why if we cut through a cabbage-stump do we find a tough
    coating enveloping a cellular substance, 1158

  Plants, why are their seeds formed within the corollas of flowers, 1168

  Plants, why does the flower of the poppy turn down during the early
    formation of seed, 1169

  Plants, why have those of the pea-tribe a folding blossom, 1170

  Plants, why are leaf-buds enclosed in scales which fall off as the
    leaves open, 1171

  Plants, what is meant by "species" of, 1209

  Plants, what is meant by "genus" of, 1210

  Plants, progressive discovery of new species, 1211

  Plants, what are the three great classes of, 1212


  LESSON LVIII.

  Plants, what are the characteristics of exogenous, 1213

  Plants, what are the characteristics of cryptogamus, 1216

  Plants, what are the effects of diverse climates upon, 1242

  Plants, what are the effects of altitude upon mountains, 1243

  Plants, what agencies influence their geographical distribution, 1250

  Plants, what are the chief facts connected with the distribution of by
    man, 1251

  Plants, why are herbaceous less solid than woody, 1265

  Plants, why are the stalks of herbaceous generally cylindrical, 1266

  Plants, what are the stomata of, 1267

  Plants, why are their stomata generally on the underside of their
    leaves, 1268

  Plants, why have they pith in their centres, 1269

  Porter, why does bottled produce large volumes of froth, 801

  Pulse, why do we feel it beat, 900


  Quadrupeds, geographical distribution of, 1331

  Quicksilver, why does it reflect light from mirrors, 513


  LESSON LIX.

  Radiation, why does scratching a bright metal surface increase its
    powers of, 199

  Radiation of heat, what benefits arise from it, 415

  Radiation of light, what is it, 503

  Radiation, do all bodies radiate light, 504

  Rain, what is it, 416

  Rain, does it ever occur without clouds, 417

  Rain-drops, why are they sometimes large, and at other times small, 418

  Rains, at what seasons are they most prevalent, 419

  Rainy days, in what months of the year are they most frequent, 420

  Rainy days, why are there more from September to March, 421

  Rain, in what part of the world does the greatest quantity fall, 422

  Rain, in what part of the world do the heaviest rains fall, 423

  Rain, in what part of the world does the least rain fall, 424

  Rainy days, how many are there in a year, 425

  Rain, in what part of England does the greatest quantity fall, 426

  Rains, why do the heaviest occur in hot countries, 427


  LESSON LX.

  Rain, why does the greatest quantity fall at the equator, 428

  Rain, why are some parts of the earth without it, 429

  Rain, why does it purify the air, 433

  Rainy localities, why are mountainous countries more rainy than flat
    ones, 434

  Rain, why does more fall by night than by day, 435

  Rain, why do bunches of dried sea-weed indicate its coming, 436

  Rain, why do weather-toys foretell its coming, 437

  Rain, the Capuchin toy; mysterious walk of a wooden horse, 438

  Rain, why does ladies' hair drop out of curl as rain approaches, 438

  Rain, why is it said to be coming, when the mountains are "putting on
    their night-caps", 439

  Rainbow, what causes a, 486

  Rainbow, why does it exhibit colours, 487

  Rainbows, why are there sometimes two, 488

  Rainbows, why are the columns of the secondary bow, arranged in the
    reverse order of those of the primary, 489


  LESSON LXI.

  Rainbow colours, why do glass lustres and chandeliers exhibit them, 498

  Rainbows, why are the colours of the secondary bow fainter than those
    of the primary, 491

  Rainbow, what is a lunar, 492

  Rainbow, why is a lunar bow fainter than the solar, 493

  Rainbow, why is one in the morning the shepherd's warning, 538

  Rainbow, why is one at night the shepherd's delight, 539

  Refraction of light, what is it, 472

  Refraction and reflection of light, what is the difference, 502

  Reflections, why are they reversed, 490

  Reflection, why do black bodies reflect any light, 505

  Reflection, why does a window-pane appear to reflect better by night
    than by day, 516

  Reflection, what is the line of, 520

  Reflection, what is the angle of, 522

  Repulsion, what is it, 792

  Respiration, why does the chest expand when we breathe, 889

  Respiration, how does blood communicate with the air in the lungs, 890

  Rest, why does it invigorate us, 1018

  Rice, where is it cultivated, 1219

  Rosewood, what is it, 1191


  LESSON LXII.

  Saliva, why does saliva enter the mouth while we are eating, 872

  Sea, why is it salt, 764

  Sea, what is the estimated amount of salt in the, 765

  Sea, what is the depth of the, 766

  Sea-gulls, why are they numerous in fine weather, 1119

  Sea-gulls, why do they fly over the land on the approach of stormy
    weather, 1120

  Sea-crow, why is its lower bill longer than the upper, 1135

  Sealing-wax, why does rubbing it attract to it small particles of
    matter, 565

  See, why do we, 963

  Seeds, why are they generally enveloped in hard cases, 1152

  Seeds, why do they throw out roots before they form leaves, 1153

  Seeds, why does the leaf-germ come up to the light and the root-germ
    penetrate the earth, 1285

  Seeds, why are they indigestible, 1286

  See-saw, why may a little boy balance a larger boy, 863

  See-saw, why does the little boy sink to the earth, when the larger boy
    kicks the ground, 861


  LESSON LXIII.

  See-saw, why may the little boy keep the larger one up, when once he is
    up, 864

  Shadows, what is the cause of, 508

  Shadows, why is there some light where shadows fall, 510

  Shadows, why do they lengthen as the sun goes down, 526

  Shuttle-cock, why does it travel slowly through the air, 836

  Shuttle-cock, why do we hear a noise when we strike it with the
    battledore, 837

  Sight, why are two persons able to see each other, 551

  Sight, why can we see so many upon the small retina, 966

  Sight, why are we able to see at long or short distances, 974

  Sigh, why do we, 1025

  Silica, what is it, 1260

  Silk, what is it, 1200

  Skin, why does a chill of the produce inflammatory action in the lungs,
    1014

  Sky, what is it, 530

  Sky, why is it red at sunset, 532

  Sleet, what is it, 447

  Sleep, what is it, 1019

  Smell, why do we, 992

  Smoke, what is it, 102

  Smoke, why is there so little when the fire is red, 105

  Smoke, what is it, 289


  LESSON LXIV.

  Smoke, why do fresh coals increase the quantity of, 291

  Smoke, why does it issue in folds and curls, 632

  Smoke, why does it ascend in mild and fine weather, 689

  Snails, why can they move in an inverted position, 666

  Snails, where do they obtain their shells, 1306

  Snails, why do their shells grow, 1307

  Snails, why are their shells spiral, 1308

  Snails, why have they four tentacula attached to their heads, 1309

  Snails, why are they able to move without feet, 1310

  Snails, why do we see none in the winter time, 1311

  Snails, why can they live in sealed shells, 1312

  Sneeze, why do we, 1024

  Snipes and woodcocks, why have they long, tapering bills, 1042

  Snore, why do we, 1028

  Snow, why does it keep the earth warm, 160

  Snow, why is it a good non-conductor of heat, 162

  Snow, what is it, 440

  Snow, why is it white, 441


  LESSON LXV.

  Snow, why is it warm, though white garments are cool, 442

  Snow, why is it always on the tops of high mountains, 443

  Snow-line, what is meant by the, 445

  Snow, what is red, 446

  Soda-water, why does it effervesce, 802

  Soils, why are clayey unfavourable to vegetation, 1160

  Soils, why are sandy unfavourable to vegetation, 1162

  Soils, why are chalk unfavourable to vegetation, 1162

  Soils, why are mixed favourable to vegetation, 1163

  Soils, why do farmers manure their land, 1165

  Soot, why should it be prevented from accumulating at the bottom and
    sides of saucepans, 205

  Soot, what is it, 290

  Sound, what is it, 716

  Sounds, what causes the air to produce, 717

  Sounds, how do we know that they are produced by vibrations, 718

  Sounds, how do we know that without air there would be none, 719

  Sounds, how are the vibrations of sonorous bodies imparted to the air,
    720


  LESSON LXVI.

  Sounds, how rapidly do the vibrations of travel, 721

  Sounds, do all sounds travel at the same rate, 722

  Sounds, why are bells and glasses stopped from ringing by touching them
    with the finger, 723

  Sounds, why does a cracked bell give discordant, 724

  Sounds, why do we see the flash of a gun before we hear the report, 725

  Sound, why does the marching of long ranks of soldiers appear to be
    irregular, 726

  Sounds, what are the numbers of vibrations that produce various, 727

  Sounds, why does the length of a wire or string influence the sounds it
    produces, 728

  Sound, why does the tension of a wire or string affect its vibrations,
    729

  Sound, why are some notes low and solemn, and others high and quick, 730

  Sound, why can our voices be heard at a greater distance when we speak
    through tubes, 731

  Sound, is air a good conductor, 732

  Sounds, why can we hear them at a greater distance on water than on
    land, 733


  LESSON LXVII.

  Sound, why do sea-shells give a murmuring noise when held to the ear,
    734

  Sound, why can people in the arctic regions converse when more than a
    mile apart, 735

  Sounds, why do savages lay their heads upon the earth to catch sounds,
    736

  Sounds, why can church clocks be heard striking more plainly at some
    times than at others, 737

  Sound, why may the scratching of a pin at one end of a long pole be
    heard at the opposite extremity, 738

  Sound, why is the hearing of deaf persons assisted by ear-trumpets, 739

  Sounding-boards, why are they used to improve the hearing of
    congregations, 740

  Sounds, why, when we are walking under arches or tunnels, do our voices
    appear louder, 747

  Spark, what causes it when a horse's shoe strikes against a stone, 340

  Specific gravity, what is it, 789

  Spiders, why have they the power of spinning webs, 1082

  Spiders, why may fine weather be expected when they build their webs,
    1108


  LESSON LXVIII.

  Spiders, why may wet weather be expected when they hide, 1109

  Spiders, why may wet weather be expected when they break off their webs
    and remove them, 1113

  Spider, why, if the webs of the gossamer fly about in autumn, may east
    winds be expected, 1124

  Spiders, gossamer, why can they float through the air, 1125

  Spinal cord, what is the, 952

  Spinal cord, why is it placed in the back-bone, 953

  Spinal-cord, how do the branches pass out from it, 954

  Spontaneous combustion, what substances are liable to it, 317

  Spontaneous combustion, has it ever occurred in living bodies, 319

  Spontaneous combustion, why does it occur in the case of the drunkard,
    320

  Spoon-bill, why has it a long expanded bill, lined with sharp, muscular
    points, 1045

  Spoon-bill, why has it long legs, 1046

  Squint, why do some people, 967

  Starch, what is it, 1202

  Star-lit nights, why are they usually colder than cloudy nights, 350

  Stars, why do they twinkle, 484


  LESSON LXIX.

  Stars, why does their twinkling foretell bad weather, 485

  Steam, why does it issue from the spout of a kettle, 750

  Storms, what is the cause of, 676

  Storms, why do the most violent occur in and near the tropics, 677

  Straw, why is it frequently used for manure, 1264

  "Sucker," why does it raise a stone, 860

  Sugar, what is it, 1197

  Sugar-cane, where is it cultivated, 1226

  Sun, what is its distance from the earth, 452

  Sun, what is the, 455

  Sun, from what does its luminosity arise, 456

  Sun and moon, why do they appear smaller when near the meridian, than
    when near the horizon, 525

  Sun, why do we see it before sunrise, and after sunset, 482

  Sun, what is the magnitude of the, 787

  Suppers, why do they cause dreams, 1021

  Swallows, why may wet weather be expected when they fly low, 1104

  Syringe, why does pressing in the handle force out a jet of water, 856

  Syringe, why will not the water run out, unless the handle is pressed
  in, 857


  LESSON LXX.

  Syringe, why will the water leak out, but not run, 858

  Syringe, why cannot the handle be pressed in, if a finger is kept on
    the orifice, 859


  Tannin, what is it, 1257

  Taste, why do we, 996

  Taste, why are some substances sweet, others sour, &c., 997

  Taste, why is it most powerful after substances have been a little
    while in the mouth, 998

  Taste, why if we put out the tongue and touch it with a nub of sugar,
    shall we perceive no taste, 999

  Taste, why when we draw in the tongue do we then perceive the taste of
    the sugar, 1000

  Taste, through what nerves are we made sensible of the contact of sugar
    with the tip of the tongue, 1001

  Taste, why do connoisseurs of wines hold wine in their mouths a few
    seconds when judging of it, 1002

  Taste, why do they also pass the fumes of the wine through their
    nostrils, 1003

  Tea-pot, why does a bright metal one produce better tea than a black
    earthenware, 200


  LESSON LXXI.

  Tea-pot, if the earthenware one were set by the fire, why would it then
    make the best tea, 201

  Tea, what is it, 1192

  Tea, where is it cultivated, 1225

  Tears, what is the cause of, 977

  Temperature, why do some articles feel colder than others, 138

  Temperature, why does it feel warmer after a frost has set in, 163

  Tendons, what are they, 939

  Tendons, why are they used to attach the muscles to the bones, 940

  Teneriffe, what are the botanical regions of the Peak of, 1241

  Thaumatrope, why do the figures on appear to dance, 869

  Thaw, why is it colder when a thaw takes place, 164

  Thermometer, what is the, 709

  Thermometer, why does it indicate degrees of heat, 710

  Thermometer, why are there Reaumur's and Fahrenheit's, 711

  Thermometer and barometer, what is the difference, 712

  Thermometer, in what season of the year does it vary most, 715

  Thunder, what is it, 614

  Thunder-peal, why is it sometimes loud and continuous, 616


  LESSON LXXII.

  Thunder-peal, why is it sometimes broken and unequal, 617

  Thunder-peal, why is it sometimes a low, grumbling noise, 618

  Thunder-peal, why does it sometimes follow immediately after the flash
    of lightning, 620

  Thunder, through what distance will the sound travel, 621

  Thunderbolt, what is a, 628

  Tinder-box, the history of a, 340

  Toasting-fork, why has it a wooden handle, 124

  Tops, why do they stand erect while they spin, but fall when they stop,
    814

  Tops, why do they "sleep", 816

  Tops, why do they cease to spin, 817

  Touch, in what part of the body is the sense of most perfect, 1005

  Toxicologists, what are they, 61

  Trap and ball, why is the ball propelled upward, when the trigger is
    struck, 866

  Trees, what are the estimated ages of, 1214

  Trees, what are the northern limits of, 1237

  Trees, why are they covered with bark, 1270


  LESSON LXXIII.

  Trees, why have those with large trunks a great number of leafy
    branches, 1274

  Trees, why have poplars comparatively few leaves, 1275

  Trees, why had the mammoth comparatively few leaves, 1276

  Trees, why have oaks an abundance of leaves, 1277

  Trees, why are their trunks generally round, 1278

  Twilight, what is the cause of, 482


  Vacuum, what is a, 649

  Vacuum, is it possible to obtain a perfect, 650

  Vegetables, have they any heat, 90

  Vegetable structures, of what do they consist, 1151

  Vegetables, why do farmers sow different crops in rotation, 1164

  Vegetables, why are the hearts of cabbages, &c., pale yellow, 1182

  Vegetable productions, why are they so widely diffused, 1189

  Vegetable eaters, why do they feed so continually, 1091

  Vegetation, geographical distribution of, 1208

  Vegetation, what are the characteristics of tropical, 1218

  Vegetation, what are the changes in on quitting the tropics, 1232


  LESSON LXXIV.

  Vegetation, what are the characteristics of, upon approaching the polar
    zones, 1234

  Vegetation, what are the characteristics of mountain, 1238

  Vines, where are their favourable climates, 1233


  Walking, why does it make us warmer, 26

  Water, what becomes of that formed by combustion, 58

  Water, is it a good or bad conductor of heat, 151

  Water, why does it extinguish fire, 306

  Water, why, when a blacksmith thrusts a hot iron into a tank, do we
    perceive a peculiar smell, 309

  Water, why does it freeze, 324

  Water, why does it become steam, 326

  Water, how many degrees of latent heat are hidden in its several
    states, 327

  Water, why does it expand when freezing, while bodies generally
    contract with cold and expand with heat, 341

  Water, why does it never freeze to a great depth, 342

  Water, how much deeper is it than it appears to be, 480


  LESSON LXXV.

  Water, why has the exceptional law, by which it expands when freezing,
    been ordained, 343

  Water, why can we seldom succeed in the first attempt to touch anything
    lying at the bottom of, 481

  Water, what causes it to flow from a pump, 651

  Water, why does it run through a syphon, 655

  Water, what is it, 748

  Water, why does it become solid when it freezes, 751

  Water, why does it boil, 753

  Water, what proportion of the earth's surface is covered by it, 554

  Water, why does it dissolve substances, 758

  Water, why does hot dissolve more readily than cold, 759

  Water, why is it sometimes hard, 760

  Water, why is rain-water soft, 761

  Water, why is it difficult to wash in hard, 763

  Waters, why are some impregnated with mineral matters, 767

  Water, why does stagnant become putrid, 769

  Water, is there danger attending drinking it on account of animalculæ,
    770

  Water, what are the means by which it may be purified, 771


  LESSON LXXVI.

  Water, what is the pressure of, 775

  Water, why will a drop upon the blade of a knife leave a dark spot, 777

  Water, why does it roll in agitated globules when dropped upon hot
    iron, 796

  Water, why does oil float upon it, 797

  Water, why is spring fresh and invigorating, 803

  Water, why is boiled flat and insipid, 804

  Weather, why does a yellow sunset foretell wet, 534

  Weather, why does a red sunset foretell fine, 535

  Weather, why does a red sunrise foretell wet, 536

  Weather, why does a grey sunrise foretell dry, 537

  Weather, barometrical indications of, 708

  Whales, why have they a large development of oily matter about their
    heads, 1068

  Whale, why has it feathery bones extending from its jaws, 1095

  Whales, why are, their eyes provided with very thick coats, 1131

  Wheat, why do the ears stand up by day and turn down by night, 1175

  Wheat, what is it, 1199


  LESSON LXXVII.

  Wheat, what is the northern limit of, 1235

  Wheat, why is silica diffused over its stem, 1261

  Wheat-crops, why do they greatly exhaust the soil, 1263

  Whirlwinds, what are they, 678

  Why do we see, 963

  Why do we wink, 975

  Why do we weep, 977

  Why do we hear, 983

  Why do we taste, 986

  Why do we smell, 992

  Why do we feel, 1004

  Why do we sleep, 1019

  Why do we dream, 1020

  Why do suppers produce dreaming, 1021

  Why do we yawn, 1022

  Why do we cough, 1023

  Why do we sneeze, 1024

  Why do we sigh, 1025

  Why do we laugh, 1026

  Why do we hiccough, 1027

  Why do we snore, 1028

  Why do we feel hungry, 1337

  Why do we feel thirsty, 1338

  Wick of a candle, why does it turn black as it burns, 225

  Wick of a candle, why is there a spark generally at the end of it, 256

  Will-o'-the-wisp, what is it, 318

  Winds, what is the cause of, 234

  Winds, why are east usually dry, 384

  Winds, why are west usually wet, 385

  Winds, why are north usually cold and dry, 386


  LESSON LXXVIII.

  Winds, why are south warm and rainy, 387

  Wind, what is it, 666

  Winds, what are the velocities of, 667

  Winds, what are trade, 668

  Winds, what is the cause of trade, 669

  Winds, why do trade winds blow from east to west, 670

  Winds, what determines the character of, 674

  Wind-mills, why do their wings turn round, 690

  Windows, why do they reflect the sun's rays in the evening, 523

  Windows, why do they not reflect the sun's rays at noon, 524

  Wood, why does decayed look luminous, 95

  Wood, burning at one end, why does it not feel hot at the other, 118

  Wood, why is it a bad conductor of heat, 119

  Wood that is green, why does it hiss and steam when burning, 285

  Wood, why does it ignite less readily than paper, 297

  Woodcocks and snipes, why have they nerves running down to the tip of
    their bills, 1043

  Woodpeckers, why do they "tap" at old trees, 1066

  Woollens, why are they worn in winter, 166

  Wool, what is it, 1201


  Yawn, why do we, 1026


  Zoological geography, 1326




[Verse: "God looked down from heaven upon the children of men, to
see if there were any that did understand that did see God."--PSALM
LIII.]




THE REASON WHY.




CHAPTER I.


1. _Why should we seek knowledge?_

Because it assists us to comprehend the _goodness and power of God_.

And it gives us power over the circumstances and associations by which
we are surrounded: the proper exercise of this power will greatly
promote our happiness.

2. _Why does the possession of knowledge enable us to exercise power
over surrounding circumstances?_

Knowledge enables us to understand that, in order to live healthily, we
require to breathe fresh and pure air. It also tells us that animal and
vegetable substances, undergoing decay, poison the air, though we may
not be able to see, or to smell, or otherwise discover the existence
of such poison. Knowing this, we become careful to remove from our
presence all such matters as would tend to corrupt the atmosphere. This
is only one of the countless instances in which knowledge gives us
power over surrounding circumstances.

3. _Name some other instances in which knowledge gives us power._

Knowledge of _Geography_ and of _Navigation_ enables the mariner to
guide his ship across the trackless deep, and to reach the sought-for
port, though he had never before been on its shores.

Knowledge of _Chemistry_ enables us to separate or to combine the
various substances found in nature. Thus we obtain useful and precious
metals from what at first appeared to be useless stones; transparent
glass from pebbles, through which no light could pass; soap from oily
substances; and gas from solid bodies.

[Verse: "Give instruction to a wise man, and he will be yet wiser;
teach a just man, and he will increase in learning."--PROVERBS IX.]

Knowledge of _Medicine_ enables the physician to overcome the ravages
of disease, and to save suffering patients from sinking prematurely to
the grave.

Knowledge of _Anatomy_ and of _Surgery_ enables the surgeon to bind up
dangerous fractures and wounds, and to remove, even from the internal
parts of bodies, ulcers and diseased formations that would otherwise be
fatal to life.

Knowledge of _Mechanics_ enables man to increase his power by the
construction of machines. The steam-ship crossing the ocean in
opposition to wind and tide, the railway locomotive travelling at
60 miles an hour, and the steam-hammer beating blocks of iron into
useful shapes, are evidences of the power which man acquires through a
knowledge of mechanics.

Knowledge of _Electricity_ enables man to stand in comparative safety
amid the awful war of the elements. Lightning, the offspring of
electricity, has a tendency to strike upon lofty objects by which
it may be attracted. By its mighty powers churches or houses may be
instantly levelled with the dust. But man, knowing that electricity
is strongly attracted by particular substances, raises over lofty
buildings rods of steel communicating with bars that descend into the
ground. The lightning, rushing with indescribable force toward the
steeple, is attracted by the bar of steel, and conducted harmlessly to
the earth. Man may thus be said to take even lightning by the hand,
and to divert its destroying force by the aid of Knowledge. And in
countless other instances "Knowledge is Power."




CHAPTER II.


4. _Why do we breathe air?_

Because the air contains _oxygen_, which is necessary to life.

5. _Why is oxygen necessary to life?_

Because it combines with the _carbon_ of the blood, and forms _carbonic
acid gas_.

[Verse: "Be not as the horse, or as the mule, which have
no understanding: whose mouth must be held with the bit and
bridle."--PSALM XXXII.]

6. _Why is this combination necessary?_

Because we are so created that the substances of our bodies are
constantly undergoing change, and this resolving of solid matter into a
gaseous form, is the plan appointed by our Creator to remove the matter
called _carbon_ from our systems.

7. _Why do our bodies feel warm?_

Because, in the union of _oxygen_ and _carbon_, heat is developed.

8. _What is this union of oxygen and carbon called?_

It is called _combustion_, which, in chemistry, means the decomposition
of substances, and the formation of new combinations, accompanied by
heat; and sometimes by light, as well as heat.

9. _What is formed by the union of oxygen and carbon?_

Carbonic acid gas.

10. _What becomes of this carbonic acid gas?_

It is sent out of our bodies by the compressure of the lungs, and
mingles with the air that surrounds us.

11. _Is this carbonic acid gas heavier or lighter than the air?_

Pure carbonic acid gas is the heaviest of all the gases. That which is
sent out of the lungs is not pure, because the whole of the air taken
into the lungs at the previous inspiration has not been deprived of its
_oxygen_, and the nitrogen is returned. Therefore the breath sent out
of the lungs may be said to consist of _air_, with a large proportion
of _carbonic acid gas_.

12. _What is the composition of air in its natural state?_

It consists of _oxygen_, _nitrogen_, and _carbonic acid gas_, in the
proportions of oxygen 20 volumes, nitrogen 79 volumes, and carbonic
acid gas 1 volume. It also contains a slight trace of watery vapour.

13. _What is the state of the air after it has once been breathed?_

It has parted with about one-sixth of its oxygen, and taken up an
equivalent of carbonic acid. And were the same air to be breathed six
times successively, it would have parted with _all_ its oxygen, and
could no longer sustain life.

[Verse: "A prudent man forseeth the evil, and hideth himself; but
the simple pass on, and are punished."--PROVERBS XXVII.]

14. _Is the impure air sent out of the lungs lighter or heavier than
common air?_

At first, being rarefied by warmth, it is _lighter_. But, if
undisturbed, it would become _heavier_ as it cooled, and would descend.

15. _Why is it proper to have beds raised about two feet from the
ground?_

Because at night, the bed-room being closed, the breath of the sleeper
impregnates the air of the room with carbonic acid gas, which,
descending, lies in its greatest density near to the floor.

16. _What are the chief sources of carbonic acid gas?_

The vegetable kingdom (as will be hereafter explained), the combustion
of substances composed chiefly of carbon, the breathing of animals, and
the decomposition of carbonic compounds.

17. _Is breathing a kind of combustion?_

It is. In the breathing of animals, the burning of coals, or of wood,
or candles, &c., similar changes occur. The _oxygen_ of the air
combines with the _carbon_ of the substance said to be burnt, and forms
_carbonic acid gas_, which unfits the air for the purposes of either
breathing or of burning, until it has been renewed by admixture with
the air.

18. _What is carbon?_

It is one of the elementary bodies, and is very abundant throughout
nature. It abounds mostly in vegetable substances, but is also
contained in animal bodies, and in minerals. The form in which it is
most familiar to us is that of _charcoal_, which is carbon almost pure.

19. _What is meant by an elementary body?_

An elementary body is one of those substances in which chemistry is
unable to discover more than one constituent. For instance, the chemist
finds that water is composed of _oxygen_ and _hydrogen_. Water is
therefore a _compound_ body. But _carbon_ consists of _carbon only_,
and therefore it is called a simple, or elementary body.

[Verse: "Where no wood is, there the fire goeth out: so where there
is no tale-bearer, the strife ceaseth."--PROVERBS XXVI.]

20. _Why is it dangerous to burn charcoal in rooms?_

Because, being composed of _carbon_ that is nearly pure, its combustion
gives off a large amount of _carbonic acid gas_.

21. _What is the effect of carbonic acid gas upon the human system?_

It induces drowsiness and stupor, which, if not relieved by
ventilation, would speedily cause death.

22. _What is the reason that people feel drowsy in crowded rooms?_

Because the large amount of carbonic acid gas given off with the
breaths of the people, makes the air poisonous and oppressive.

23. _What other causes of drowsiness are there?_

The candles, gas, or fires that may be burning in the rooms where
people are assembled. Three candles produce as much carbonic acid gas
as one human being; and it is probable that one gas-light produces as
much carbonic acid gas as two persons.

24. _Have people ever been poisoned by their own breaths?_

In the reign of George the Second, the Rajah of Bengal took some
English prisoners in Calcutta, and put 146 of them into a place which
was called the "Black Hole." This place was only 18 feet square by 16
feet high, and ventilation was provided for only by two small grated
windows. _One hundred and twenty-three of the prisoners died in the
night_, and most of the survivors were afterwards carried off by putrid
fevers. Many other instances have occurred, but this one is the most
remarkable.




CHAPTER III.


25. _What is oxygen?_

Oxygen is one of the most widely diffused of the elementary substances.
It is a gaseous body.

[Verse: "Stand in awe and sin not: commune with your own heart upon
your bed and be still"--PSALM IV.]

26. _Why do persons who are walking, or riding upon horseback feel
warmer than when they are sitting still?_

Because as they breathe more rapidly, the combustion of the _carbon_
in the blood is increased by the _oxygen_ inhaled, and greater heat is
developed.

27. _Why does the fire burn more brightly when blown by a bellows?_

Because it receives, with every current of air, a fresh supply of
_oxygen_, which unites with the _carbon_ and _hydrogen_ of the coals,
causing more rapid combustion and increased heat.

28. _Why does not the oxygen of the air sometimes take fire?_

Because oxygen, _by itself_, is incombustible. The wick of a candle,
which retains the slightest spark, being immersed in oxygen, will
instantly burst into a brilliant flame; and even a piece of iron wire
made red-hot, and dipped in oxygen, will burn rapidly and brilliantly.
Oxygen, though non-combustible of itself, is the most powerful
_supporter of combustion_.

29. _Why do we know that oxygen will not burn of itself?_

Because when we immerse a burning substance into a jar of oxygen, it
immediately burns with intense brilliancy; but directly it is withdrawn
from the oxygen, the intensity of the flame diminishes, and the oxygen
which remains is _unaffected_.

30. _Why do we know that oxygen is necessary to our existence?_

Because animals placed in any kind of gas, or in any combination of
gases, where oxygen _does not exist_, die in a very short time.

31. _Where is oxygen found?_

It is found in the air, mixed with _nitrogen_; in water combined with
_hydrogen_; in the tissues of vegetables and animals; in our blood; and
in various compounds called, from the presence of oxygen, _oxides_.

32. _Why is the oxygen of the air mixed so largely with nitrogen?_

Because _oxygen_ in any greater proportion than that in which it is
found in the atmosphere, would be too exciting to the animal system.
Animals placed in _pure oxygen_ die in great agony from fever and
excitement, amounting to madness.

[Verse: "As vinegar is to the teeth, and as smoke to the eyes, so is
the sluggard to him that sent him."--PROVERBS X.]

33. _What is nitrogen?_

Nitrogen is an elementary body in the form of gas.

34. _Where is nitrogen found?_

It is chiefly found in the air, of which it constitutes 79 out of 100
volumes. It may be mixed with oxygen in various proportions; but in the
atmosphere it is uniformly diffused. It is found in most animal matter,
_except fat and bone_. It is not a constituent of the _vegetable
acids_, but it is found in most of the _vegetable alkalies_.

35. _What are acids?_

Acids are a numerous class of chemical bodies. They are generally sour.
Usually (though there are exceptions) they have a great affinity for
water, and are easily soluble therein; they unite readily with most
_alkalies_, and with the various _oxides_. All acids are compounds of
two or more substances. Acids are found in all the kingdoms of nature.

36. _What are alkalies?_

Alkalies are a numerous class of substances that have a great affinity
for, and readily combine with, _acids_, forming _salts_. They exercise
peculiar influence upon vegetable colours, turning blues green, and
yellows reddish brown. But they will restore the colours of vegetable
blues which have been reddened by _acids_; and, on the other hand,
the _acids_ restore vegetable colours that have been altered by the
_alkalies_. Alkalies are found in all the kingdoms of nature.

37. _Could animals live in nitrogen?_

No; they would immediately die. But a mixture of _oxygen_ and
_nitrogen_, in equal volumes, constitutes _nitrous oxide_, which gives
a pleasurable excitement to those who inhale it, causing them to be
merry, almost to insanity; it has, therefore, been called _laughing
gas_.

38. _Why does nitrous oxide produce this effect?_

Because it introduces into the body more _oxygen_ than can be consumed.
It, therefore, deranges the nervous system, and being a powerful
stimulant, gives an unnatural activity to the nervous centres and the
brain.

[Verse: "Lord, make me know mine end, and the measure of my days,
that I may know how frail I am."--PSALM XXXIX.]

39. _In what proportions are the atmospheric gases found in the blood?_

The mean quantity of the gases contained in the human blood has been
found to be equal to 1-10th of its whole volume. In _venous_ blood, the
average quantity of _carbonic acid_ is about 1-18th, that of _oxygen_
about 1-85th, and that of _nitrogen_ about 1-100th of the volume of
the blood. In _arterial_ blood their quantities have been found to be
_carbonic acid_ about 1-14th, _oxygen_ about 1-38th, and _nitrogen_
about 1-72nd.

40. _Then is nitrogen taken into the blood from the air?_

Such a supposition is highly improbable. It is probably derived
from _nitrogenised food_, just as _carbonic acid_ is derived from
_carbonised food_.

41. _What is venous blood?_

Venous blood is that which is returning through the _veins_ of the body
from the organs to which it has been circulated.

42. _What is arterial blood?_

Arterial blood is that which is flowing from the heart through the
_arteries_ to nourish the parts where those arteries are distributed.

43. _What is the difference between venous and arterial blood?_

Venous blood contains _more_ carbonic acid, and _less_ oxygen and
nitrogen than arterial blood.

44. _Will nitrogen burn?_

It will not burn, nor will it support combustion.

45. _What is the difference between "burning" and "supporting
combustion?"_

Oxygen gas will not burn of itself, but it aids the decomposition
by fire of bodies that are combustible. It is therefore called a
_supporter of combustion_. But hydrogen gas, _though it burns of
itself_ will extinguish a flame immersed in it. It is therefore said
to be a body which will _burn_, but _will not support combustion_.

[Verse: "As coals are to burning coals, and wood to fire; so is a
contentious man to kindle strife."--PROVERBS XXVI.]

46. _What becomes of the nitrogen that is inhaled with the air?_

It is thrown off with the breath, mixed with _carbonic acid gas_, and
flies away to be renewed by a fresh supply of oxygen.

47. _Where does nitrogen find a fresh supply of oxygen?_

In the atmosphere. Nitrogen is said to possess a remarkable tendency to
_mix_ with oxygen, without having a positive chemical _affinity_ for
it. That is to say, neither the _oxygen_ nor the _nitrogen_ undergoes
any change by the union, except that of _admixture_. The oxygen and
the nitrogen still possess their own peculiar properties. Oxygen and
nitrogen are found in nearly the same proportions in all climates, and
at all altitudes.

48. _In combustion does any other result take place besides the union
of oxygen and carbon forming carbonic acid gas?_

Yes. Usually _hydrogen_ is present, which in burning unites with
_oxygen_, and forms _water_.




CHAPTER IV.


49. _What is hydrogen?_

Hydrogen is an elementary gas, and is the lightest of all known bodies.

50. _Will hydrogen support animal life?_

It will not. It proves speedily fatal to animals.

51. _Will hydrogen support combustion?_

Although it will burn, yielding a feeble bluish light, it will, if
pure, extinguish a flame that may be immersed in it. Hydrogen will
therefore _burn_, but will not _support combustion_.

52. _Why will hydrogen explode, if it will not support combustion?_

When hydrogen explodes it is always in combination with _oxygen_,
or with the common air, which contains _oxygen_. _Two_ measures of
hydrogen and _one_ of oxygen form a most explosive compound.

[Verse: "As smoke is driven away, so drive them away: as wax
melteth before the fire, so let the wicked perish at the presence of
God."--PSALM XLVI.]

53. _Why does hydrogen explode, when mixed with oxygen, upon being
brought in contact with fire?_

Because of its strong affinity for _oxygen_, with which, upon the
application of heat, it unites to form water.

54. _Where does hydrogen chiefly exist?_

In the form of _water_, where it exists in combination with _oxygen_.
_Eleven_ parts of hydrogen, and _eighty-nine_ of oxygen, form water.

55. _Is hydrogen found elsewhere?_

It is never found but in a state of combination; united with oxygen,
it exists in _water_; with nitrogen, in _ammonia_; with chlorine, in
_hydro-chloric acid_; with fluorine, in _hydro-fluoric acid_; and in
numerous other combinations.

56. _Is the gas used to illuminate our streets, hydrogen gas?_

It is; but it is combined with carbon, derived from the coals from
which it is made. It is therefore called _carburetted hydrogen_, which
means _hydrogen_ with _carbon_.

57. _How is hydrogen gas obtained from coals?_

It is driven out of the coals by heat, in closed vessels, which prevent
its union with _oxygen_.

58. _What becomes of the water which is formed by the burning of
hydrogen in oxygen?_

It passes into the air in the form of watery vapour. Frequently it
condenses, and may be seen upon the walls and windows of rooms where
many lights or fires are burning. Sometimes, also, portions of it
become condensed in the globes of the glasses that are suspended over
the jets of gas. _A large volume of these gases forms only a very small
volume of water._

59. _What becomes of the carbonic acid gas which is produced by
combustion?_

It is diffused in the air, which should be removed by adequate
ventilation.

[Verse: "I will both lay me down in peace and sleep: for thou, Lord,
only, makest me dwell in safety."--PSALM IV.]

60. _What proportion of carbonic acid gas is dangerous to life?_

Any proportion over the natural one of 1 per cent. may be regarded as
_injurious_. But toxicologists state that _five per cent._ of carbonic
acid gas in the atmosphere is _dangerous_ to life.

61. _What are toxicologists?_

Persons who study the nature and effects of poisons and their antidotes.

62. _Which kind of combustible used for lighting tends most to vitiate
the air?_

Assuming all the lights to be of the same intensity, the degree in
which the substances burnt would vitiate the atmosphere may be gathered
from the number of minutes each would take to exhaust a given quantity
of air. This has been found to be: rape oil, 71 minutes; olive oil, 72;
Russian tallow, 75; town tallow, 76; sperm oil, 76; stearic acid, 77;
wax candles, 79; spermaceti candles, 83; common coal gas, 98; canal
coal gas, 152. Thus it is shown that rape oil is _most destructive_ of
the atmosphere, and that coal gas is the _least destructive_.

63. _Is an escape of hydrogen gas from a gas-pipe dangerous to life?_

It is dangerous, first, by _inhalation_. There are no less than six
deaths upon record of persons who were killed by sleeping in rooms near
to which there was a leakage of gas.

It is dangerous, secondly, by _explosion_.

     In 1848, an explosion of gas occurred in Albany-street,
     Regent's-park, London. The gas accumulated in a shop for a very
     short time only. It had been escaping from a crack in the meter
     for about one hour and twenty minutes. The area of the room was
     about 1,620 cubic feet. When the gas exploded, it blew out the
     entire front of the premises, carried two persons through a window
     into an adjoining yard, and forced another person on to the
     pavement on the opposite side of the street, where she was killed.
     The effect of the explosion was felt for more than a quarter of
     a mile on each side of the house, and most of the windows in the
     neighbourhood were shattered. The iron railings over the area of
     the house directly opposite were snapped asunder; and a part of
     the roof, and the back windows of another house, were carried to
     a distance of from 200 to 300 yards. The pavement was torn up
     for a considerable length, and the damage done to 103 houses
     was afterwards reported to amount to £20,000. Other serious
     explosions have taken place. The explosions of "_coal damp_,"
     which frequently occur in mines, are of a similar character.

[Verse: "O Lord, our Lord, how excellent is thy name in all the
earth! who hast set thy glory above the heavens."--PSALM VIII.]

64. _What proportion of hydrogen gas with atmospheric air will explode?_

According to the researches of Sir Humphrey Davy, _seven_ or _eight_
parts of _air_, to _one_ of _gas_, produce the greatest explosive
effect; while _larger_ proportions of gas are less dangerous. A mixture
of _equal parts_ of gas and air will burn, but it will not explode.
The same is the case with a mixture of _two_ of _air_, or _three_ of
_air_, and _one_ of _gas_; but _four_ of _air_ and _one_ of _gas_ begin
to be explosive, and the explosive tendency increases up to _seven_
or _eight_ of _air_ and _one_ of _gas_, after which the increased
proportion of gas diminishes the force of the explosion.

65. _What is the best method of preventing the explosion of gas?_

Observe the rule, _never to approach a supposed leakage with a light_.
Fortunately the gas, which threatens our lives, warns us of the danger
by its pungent smell. The first thing to be done is to open windows
and doors, and to ventilate the apartment. Then turn the gas off at
the main, and wait a short time until the accumulated gas has been
dispersed.

66. _Does hydrogen gas rise or fall when it escapes?_

Being _twelve times lighter than common air_ it _rises_, and therefore
it would be better for ventilation to open the window at the _top_ than
at the _bottom_. But all gases exhibit a strong tendency to _diffuse
themselves_, and therefore they do not rise or fall in the degree that
might be anticipated.

67. _What proportion of hydrogen in the air is dangerous to life, if
inhaled?_

One-fiftieth part has been found to have a _serious effect_ upon
animals. The effects it produces upon the human system are those of
depression, headache, sickness, and general prostration of the vital
powers. It is therefore advisable to observe precautions in the use of
gas.

[Verse: "From the place of his habitation he looketh upon all the
inhabitants of the earth."--PSALM XXXIII.]

68. _What proportion of gas in the air may be recognised by the smell?_

By persons of acute powers of smelling it may be recognised when there
is _one_ part of _gas_ in _five hundred parts of atmospheric air_; but
it becomes very perceptible when it forms _one_ part in _a hundred and
fifty_. Warning is, therefore, given to us long before the point of
danger arrives.

69. _What other sources of hydrogen are there in our dwellings?_

It arises from the decomposition of animal and vegetable substances,
containing _sulphur_ and _hydrogen_. These give off a gas called
_sulphuretted hydrogen_, from which the fætid effluviam of drains
and water-closets chiefly arise. We should, therefore, take every
precaution to secure effective drainage, and to keep drain-traps in
proper order.

70. _May the use of gas for purposes of illumination be considered
highly dangerous?_

Not if it is intelligently managed. The appliances for the regulation
of gas are so very simple and perfect, that accidents seldom arise
except from neglect. In England 6,000,000 tons of coal are usually
consumed in the manufacture of gas, producing 60,000,000,000 cubic feet
of gas. And yet accidents are of very uncommon occurrence.




CHAPTER V.


71. _What is heat?_

Heat is a principle in nature which, like light and electricity, is
best understood by its _effects_. We popularly call that heat, which
raises the temperature of bodies submitted to its influence.

72. _What is caloric?_

Caloric is another term for heat. It is advisable, however, to use the
term _caloric_ when speaking of the _cause_ of heat, and of _heat_ as
the _effect_ of the presence of _caloric_.

[Verse: "While the earth remaineth, seed-time and harvest, and
cold and heat, and summer and winter, and day and night, shall not
cease."--GEN. VIII.]

73. _What is the source of caloric?_

The sun is its chief source. But caloric, in some degree, exists _in
every known substance_.

74. _What are the effects of caloric?_

Heat which, in proportion to its intensity, acts variously upon all
bodies, causing _expansion_, _fusion_, _evaporation_, _decomposition_,
_&c._

75. _Why is caloric called a repulsive agent?_

Because its chief effects are to _expand_, _fuse_, _evaporate_, or
_decompose_ the substances upon which it acts.

76. _What is an attractive agent, in contradistinction to a repulsive
agent?_

Chemical attraction, or affinity, is an attractive agent--as when
bodies seek of their own natures to unite and form some new body.

77. _When is a body said to be hot?_

When it holds so much _caloric_ that it diffuses heat to surrounding
objects.

78. _When is a body said to be cold?_

When it holds less _caloric_ than surrounding objects, and absorbs heat
from them.

79. _How may caloric be excited to develop heat?_

By any means which cause agitation, or produce an active change in the
condition of bodies. Thus friction, percussion, sudden condensation
or expansion, chemical combination, and electrical discharges, all
develope _heat_.

80. _Why do "burning glasses" appear to set fire to combustible
substances?_

Because they gather into one point, or _focus_, several rays of
_caloric_ as they are travelling from the sun, and the accumulation of
caloric developes that intensity of _heat_ which constitutes _fire_.

81. _What is a focus?_

In optics, it is the point or centre at which, or around which,
divergent rays are brought into the closest possible union.

[Verse: "Yet man is born to trouble, as the sparks fly upward.--I
would seek unto God, and unto God would I commit my cause."--JOB V.]

82. _What is fire?_

It is a violent chemical action attending the combustion of the
ingredients of _fuel_ with the _oxygen_ of the air.

83. _What are the properties of fire?_

It imparts heat, which has the effect of expanding both fluids and
solids.

It cannot exist without the presence of combustible materials.

It has a tendency to diffuse itself in every direction.

It cannot exist without oxygen or atmospheric air.

84. _What elements take part in the maintenance of a fire?_

Hydrogen, carbon, and oxygen. Hydrogen and carbon exist in the _fuel_,
and oxygen is supplied by the _air_.

85. _How does the combustion of a fire begin?_

A match made of phosphorous and sulphur (highly inflammable substances)
is drawn over a piece of sand-paper; the _friction_ of the match
induces the presence of _caloric_, which developes _heat_, and ignites
the match, the burning of which is sustained by the _oxygen_ of the
air. The flame is then applied to paper or wood, and the heat of the
flame is sufficient to drive out _hydrogen gas_, which unites with the
_oxygen_ of the air, and burns, imparting greater heat to the _carbon_
of the coals, which assumes the form of carbonic acid gas by union with
_oxygen_, and in a little while all the conditions of _combustion_ are
established.

86. _What are the properties of heat?_

It may exist without _fire_ or _light_.

It is not sensible to _vision_.

It makes an impression upon our _feelings_.

It acts powerfully upon _all bodies_.

It has no _weight_.

It attends, or is connected with, _all the operations of nature_.

It radiates from _all bodies_ in straight lines, and in all
_directions_.

It strikes most powerfully in _direct lines_.

Its rays may be collected into a _focus_, just as the rays of the sun.

It may be _reflected_ from a polished surface.

It is more easily _conducted_ by some substances than by others.

[Verse: "For my days are consumed like smoke, and my bones are
burned as an hearth."--PSALM CII.]

87. _What is animal heat?_

Animal heat is derived from the slow combustion of _carbon_ in the
blood of animals with the _oxygen_ of the air which the animals breathe.

88. _What is latent heat?_

Latent heat (or more properly _latent caloric_) is that which exists,
in some degree, in all _bodies_, though it may be imperceptible to the
_senses_.

89. _Is there latent caloric in ice, snow, water, marble, &c?_

Yes; there is some amount of _caloric_ in all substances.

     A blacksmith may hammer a small piece of iron until it becomes
     _red hot_. With this he may light a match, and _kindle the fire
     of his forge_. The iron has become more dense by the hammering,
     and it cannot again be heated to the same degree by similar
     means, until it has been exposed _in fire_, to _a red heat_. Is
     it not possible that, by hammering, the particles of iron have
     been driven closer together, and _the latent heat_ driven out?
     No further hammering will force the atoms nearer, and therefore
     no further heat can be developed. But when the iron has _again
     absorbed caloric_, by being plunged in a fire, it is again charged
     with latent heat. Indians produce _sparks_ by rubbing together
     _two pieces of wood_. Two pieces of ice may be rubbed together
     until sufficient warmth is developed to _melt them both_. The
     axles of railway carriages frequently become _red hot_ from
     _friction_.

90. _Have vegetables heat?_

Yes; whenever oxygen combines with carbon to form carbonic acid gas,
an extrication of heat takes place, however minute the amount. Such
a combination occurs much more extensively during the germination of
seeds and the impregnation of flowers, than at any other time. In the
germination of barley heaped in rooms, previous to being converted
into malt, it is well known that a _considerable amount of heat is
developed_.

91. _Has any investigation of this subject ever been carefully made?_

Yes. Lamarck, Senebier, and De Candolle, found the flowers of the
_Arum Maculatum_, between three and seven o'clock in the afternoon, as
much as 7 deg. Reaum. warmer than the external air. Schultz found a
difference of 4 deg. to 5 deg. between the heat of the spathe of the
_Canadian pinnatifolium_ and the surrounding air, at six to seven
o'clock p.m. Other observations have established differences of as
much as 30 deg. between the temperature of the spathe of the _Arum
cordifolium_, and that of the surrounding atmosphere.

[Verse: "And there are diversities of operations, but it is the
same God which worketh in all."--CORINTHIANS XII.] 92. _Have plants
sometimes a temperature lower than that of the surrounding air?_

Yes. It has not only been found that under particular circumstances
the heat of certain parts of plants is elevated to a very remarkable
degree, but that, under nearly all circumstances, they have a
temperature different from that of the external air, being _warmer in
winter, and cooler in summer_.




CHAPTER VI.


93. _How many kinds of combustion are there?_

There are _three_, viz., slow oxydation, _when little or no light is
evolved_; a more rapid combination, _when the heat is so great as to
become luminous_; and a still more energetic action, _when it bursts
into flame_.

94. _Why does phosphorous look luminous?_

Because it is undergoing slow _combustion_.

95. _Why do decayed wood, and putrifying fish, look luminous?_

Because they are undergoing slow _combustion_. In these cases the heat
and light evolved are at no one time very considerable. But the _total
amount of heat_, and probably of _light_, generated through the lengthy
period of this slow oxydation, _amounts to exactly the same as would be
evolved during the most rapid combustion of the same substances_.

96. _What is flame?_

It is gaseous matter burning at a _very high temperature_.

97. _Why, when we put fresh coals upon a fire, do we hear the gas
escaping from the coals without taking fire?_

Because, the fire being slow, the temperature is not high enough to
ignite the gas.

[Verse: "I will praise thee, O Lord, with my whole heart; I will
show forth thy marvellous work."--PSALM IX.]

98. _What is the gas which escapes from the coals?_

Carburetted hydrogen.

99. _Why, if we light a piece of paper, and lay it where the gas is
escaping from the coals, will it burst into flame?_

Because the lighted paper gives a _heat sufficient_ to ignite the gas;
and because also hydrogen requires the contact of _flame_ to ignite it.

100. _Why, when the coals have become heated, will the hydrogen burst
into flame?_

Because the _carbon_ of the coals, and the _oxygen_ of the air, have
begun to combine, and have greatly increased the _heat_, and have
produced a rapid combustion, _so nearly allied to flame_, that it
_ignites the hydrogen_.

101. _What temperature is required to produce flame?_

That depends upon the nature of the combustible you desire to burn.
Finely divided phosphorous and phosphorated hydrogen will take fire at
a temperature of 60 deg. or 70 deg.; solid phosphorous at 140 deg.;
sulphur at 500 deg.; hydrogen and carbonic oxide at 1,000 deg. (red
heat); coal gas, ether, turpentine, alcohol, tallow, and wood, at
about 2,000 deg. (incipient white heat). When once inflamed they will
_continue to burn_, and will maintain a very high temperature.

102. _What is smoke?_

Smoke consists of small particles of _carbon_ of _hydrogen gas_, and
_other volatile matters_, which are driven off by heat and carried up
the chimney.

103. _Is it not a waste of fuel to allow this matter to escape?_

It is, as it might all be burnt up by better management.

104. _How may the waste be avoided?_

By putting on only a little coals at a time, so that the heat of the
fire shall be sufficient to consume these volatile matters as they
escape.

[Verse: "And the strong shall be as tow, and the maker of it as
a spark, and they shall both burn together, and none shall quench
them."--ISAIAH I.]

105. _Why is there so little smoke when the fire is red?_

Because the _hydrogen_ and the _volatile_ parts of the _coal_ have
already been driven off and consumed, and the combustion that continues
is principally caused by the _carbon_ of the coals, and the oxygen of
the air.

106. _Will carbon, burnt in oxygen, produce flame and smoke?_

It burns brightly, but it produces neither flame nor smoke.

107. _Why do not charcoal and coke fires give flame?_

Because the _hydrogen_ has been driven off by the processes by which
charcoal and coke are made.

108. _What is a conductor of heat?_

A conductor of heat is any substance through which heat is _readily
transmitted_.

109. _What is a non-conductor of heat?_

A non-conductor is any substance through which heat will _not_ pass
readily.

110. _Name a few good conductors._

Gold, silver, copper, platinum, iron, zinc, tin, stone, _and all dense
solid bodies_.

111. _Name a few non-conductors._

Fur, wool, down, wood, cotton, paper, and _all substances of a spongy
or porous texture_.

112. _How is heat transmitted from one body to another?_

By Conduction, Radiation, Reflection, Absorption and Convection.

113. _What is the Conduction of heat?_

It is the communication of heat from one body to another _by contact_.
If I lay a penny piece upon the hob, it becomes hot by _conduction_.

114. _What is the Radiation of heat?_

The transmission of heat by a _series of rays_. If I hold my hand
before the fire, the rays of heat fall upon it, and _my hand receives
the heat through radiation_.

[Verse: "Sing praises to the Lord, which dwelleth in Zion, declare
among the people his doings."--PSALM IX.]

115. _What is the Reflection of heat?_

The reflection of heat is the _throwing back_ of its rays towards the
direction whence they came. In a Dutch oven the rays of heat pass from
the fire to the oven, and are _reflected_ back again by _the bright
surface of the tin_. There is, therefore, considerable economy of heat
in ovens, and other cooking utensils constructed upon this plan.

116. _What is the Absorption of heat?_

The absorption of heat is the taking of it up by the body to which
it is transmitted or conducted. Heat was conveyed to my hand by
_radiation_, and _taken up_ by my hand by _absorption_.

117. _What is the Convection of heat?_

The convection of heat is the transmission of it _through_ a body or
a number of bodies, or particles of bodies, by those substances which
_first received it_; as when hot water rises from the bottom of a
kettle and imparts heat to the cold water lying above it.




CHAPTER VII.


118. _Why does not a piece of wood which is turning at one end, feel
hot at the other end?_

Because wood is _a bad conductor of heat_.

119. _Why is wood a bad conductor of heat?_

Because the arrangement of the particles of which it is composed does
not favour the transmission of _caloric_.

120. _Why do some articles of clothing feel cold, and others warm?_

Because some are bad conductors of heat, _and do not draw off much of
the warmth of our bodies_; while others are _better conductors_, and
_take up a larger portion of our warmth_.

[Verse: "The fining pot is for silver, and the furnace for gold: but
the Lord trieth the hearts."--PROVERBS XVII.]

121. _Which feels the warmer, the conductor or non-conductor?_

The non-conductor, as it does not readily _absorb_ the warmth of our
bodies.

122. _What substances are the best conductors of heat?_

Gold, silver, copper, and most substances of close and hard formation,
&c.

123. _What substances are the worst conductors of heat?_

Fur, eider down, feathers, raw silk, wood, lamp-black, cotton, soot,
charcoal, &c.

124. _Why has the toasting-fork a wooden handle?_

Because wood is not _so good a conductor_ as metal, therefore the wood
prevents the heat from being transmitted _by conduction_ to our hands.

125. _Why has the coffee-pot a wooden handle?_

Because the metal of the coffee-pot would otherwise _conduct the heat
to the hand_; but wood, _being a bad conductor_, prevents it.

126. _Why does hot water in a metal jug feel hotter than in an
earthenware one?_

Because metal, being a good conductor, _readily delivers heat to the
hand_; but _earthenware, being an indifferent conductor_, parts with
the heat slowly.

127. _How can we ascertain that wood prevents the conduction of heat to
the hand?_

By passing the top of the finger along the wooden handle of the
coffee-pot, until it reaches the point where the wood meets the metal.
The wooden handle will be found to be _cool_, but the metal will feel
_very hot_.

128. _Of what use are kettle-holders?_

Being made of _bad conductors_, such as wood, paper, or woollen cloth,
they will not readily _conduct_ the heat from the kettle to the hand.

[Verse: "Wisdom is the principal thing; therefore get wisdom: and
with all thy getting get understanding."--PROVERBS IV.]

129. _Will a kettle-holder, being a bad conductor, sometimes conduct
heat to the hand?_

Yes. But so slowly that the hand will not _feel the inconvenience of
too much heat_.

130. _Why does hot metal feel hotter than heated wool, though they may
both be of the same degree of temperature?_

Because metal gives out heat _more rapidly than wool_, by which it is
made _more perceptible to our feelings_.

131. _Which would become cold first--the metal or the wool?_

The _wool_, because, although the metal conducts heat more rapidly, to
a substance in contact with it, it does not _radiate heat_ as well as a
_black and rough substance_.

132. _Why do iron articles feel intensely cold in winter?_

Because iron is one of the best conductors, and draws off heat from the
hand very rapidly.

133. _What is the cause of the sensation called cold?_

When we feel cold, heat is being _drawn off from our bodies_.

134. _What is the cause of the sensation called heat?_

When we feel hot, our bodies are _absorbing heat_ from external causes.

     The condition here implied is that of health, and of ordinary
     circumstances. A person in a condition of fever, suffering from
     intense heat arising from a diseased state of the blood, could not
     be said to be _absorbing heat_. Nor could such a description apply
     to a person who, by a very rapid walk, has raised the temperature
     of his body considerably above its natural state, by the _internal
     combustion_ which has already been described. A person feeling hot
     in bed, from excessive clothes, feels hot from the _development of
     heat internally_, which is not _conducted away_ with sufficient
     rapidity to maintain the natural temperature of the body.

135. _If a person, sitting before a fire-place, without a fire, were
to set one foot upon a rug, and the other upon the stone hearth, which
would feel the colder?_

The foot on the stone, because stone is a good conductor, and would
_conduct the warmth of the foot away from it_.

[Verse: "The earth is the Lord's, and the fulness thereof; the
world, and they that dwell therein."--PSALM XXIV.]

136. _What does the hearth-stone do with the heat that it receives?_

It delivers it to the surrounding air, and to any other bodies with
which it may be _in contact_--and as it parts with heat, _it takes up
more from any body hotter than itself_.

137. _When there is no fire in a room, what is the relative temperature
of the various things in the room?_

They are all of the same temperature.

138. _If all the articles in the room are of the same temperature, why
do some feel colder than others?_

Because they differ in their relative powers of _conduction_. Those
that are the best conductors feel coldest, as they convey away the heat
of the hand most rapidly.

     If you lay your hand upon the _woollen table cover_, or upon the
     _sleeve of your coat_ or mantle, it will feel _neither warm nor
     cold_, under ordinary circumstances. But if you raise your hand
     from the table cover, or coat, and lay it on the marble mantel
     piece, the mantel-piece will feel _cold_. If now you return
     your hand from the mantel-piece to the table cover or coat, _a
     sensation of warmth will become distinctly perceptible_. This will
     afford a good conception of the relative _powers of conduction of
     wool and marble_.

139. _How long does a substance feel cold or hot to the touch?_

Until it has brought the part touching it to the same temperature as
itself.

140. _When do substances feel neither hot nor cold?_

When they are of the same temperature as our bodies.

141. _Why, under these circumstances, do they feel neither hot nor
cold?_

Because they neither take heat from, nor supply it to, the body.

142. _Which would feel the warmer, when the fire was lighted, the
hearth-rug or the hearth-stone?_

The hearth-stone, because it is a _good conductor_, and would not
only _receive heat_ readily, but would _part with it as freely_
(thereby making its heat _perceptible_). But the hearth-rug, _being
a bad conductor_, would part with its heat very slowly, and it would
therefore be _less perceptible_.

[Verse: "Fire and hail; snow and vapour; stormy wind fulfilling his
word."--PSALM CXLVIII.]

143. _Would the hearth-stone feel hotter than the hearth-rug though
both were of the same temperature?_

It would feel _hotter than the hearth-rug_, because it would part with
its heat so rapidly that it would be the _more perceptible_.

144. _But if the hearth-stone and the hearth-rug were both colder than
the hand, which would feel the colder of the two?_

Then the hearth-stone would feel the colder, because, _being a good
conductor_, it would _take heat_ from the hand more freely than the
hearth-rug, which is a _bad conductor_.

145. _Why would the hearth-stone feel comparatively hotter in the one
case, and colder in the other?_

Because, _being a good conductor_, it would conduct heat rapidly _to_
the hand when hot, and take heat rapidly _from_ the hand when cold.




CHAPTER VIII.


146. _Which are the better conductors of heat, fluids or solids?_

Generally speaking, _solids_, especially those of them that are dense
in their substance.

147. _Why are dense substances the best conductors of heat?_

Because the heat more readily travels from particle to particle until
it pervades the mass.

148. _Why are fluids bad conductors of heat?_

Because of the want of _density_ in their bodies; and because a portion
of the imbibed heat always passes off from fluids by _evaporation_.

[Verse: "He casteth forth his ice like morsels: who can stand before
his word,"--PSALM CXLVII.]

149. _Why are woollen fabrics bad conductors of heat?_

Because there is a considerable amount of _air_ occupying the spaces of
the texture.

150. _Is air a good or a bad conductor?_

Air is a _bad conductor_, and it chiefly transmits heat, as water does,
by _convection_.

151. _Is water a good or a bad conductor?_

Water is an indifferent conductor, but it is a _better conductor than
air_.

152. _Why, when we place our hands in water, which may be of the same
temperature as the air, does the water feel some degrees colder?_

Because water, _being a better conductor than air_, takes up the warmth
of the hand _more rapidly_.

153. _Why, when we take our hands out of water do they feel warmer?_

Because the air does not abstract the heat of the hand so rapidly as
the water did, and the change in the degree of rapidity with which the
heat is abstracted _produces a sensation of increased warmth_.

154. _Why do we see blocks of ice wrapped in thick flannel in summer
time?_

Because the flannel, being a non-conductor, prevents the _external
heat_ from _dissolving the ice_.

     Flannel wrapped around a _warm_ body _keeps in its heat_; and
     wrapped around a _cold_ body, prevents heat from _passing into it_.

155. _How do we know that air is not a good conductor of heat?_

Because, _in still air_, heat would travel to a given point much more
rapidly, and in greater intensity, through even an indifferent _solid
conductor_, than it would through the _air_.

156. _How do we know that water is not a good conductor of heat?_

Because in a deep vessel containing _ice_, and with heat applied at the
top, some portion of the water may be made to boil _before the ice,
which lies a little under the surface, is melted_.

[Verse: "As snow in summer, and as rain in harvest; so honour is not
seemly for a fool."--PROV. XXVI.]

157. _Why would you apply the heat at the top, in this experiment?_

Because in heating water it _expands and rises_. The boiling of water
is caused by the heated water _ascending from the bottom_, and the
colder water descending to occupy its place. If the heat were not
applied at the top, it would be distributed quickly by _convection_,
but not by _conduction_.

158. _Why are bottles of hot water, used as feet-warmers, wrapped in
flannel?_

Because the flannel, _being a bad conductor_, allows the heat to _pass
only gently_ from the bottle, and preserves the warmth for a _much
longer time_.

159. _Why are hot rolls sent out by the bakers, wrapped up in flannel?_

Because the flannel, _being a bad conductor_, does not _carry off
rapidly the heat of the rolls_.

160. _Why is it said that snow keeps the earth warm?_

Because snow is a _bad conductor_, and prevents the frosty air from
_depriving the earth of its warmth_.

161. _Why are snow huts which the Esquimaux build found to be warm?_

Because snow, _being a bad conductor_, keeps in _the internal heat of
the dwelling_, and prevents the _cold outer air from taking away its
warmth_.

162. _Why is snow, being composed of congealed water (and water being a
better conductor than air), so good a non-conductor?_

Because in the process of congealation it is frozen into crystalline
forms, which, being collected into a mass, form a woolly body, thus
proving the truthfulness of the Bible simile, which says, God "giveth
snow like wool."

[Verse: "He giveth snow like wool: he scattereth the hoar frost like
ashes."--PSALM CXLVII.]

[Illustration: CRYSTALS OF SNOW, AS SEEN THROUGH A MICROSCOPE. FIG. 1.]

163. _Why does it frequently feel warmer after a frost has set in?_

Because, in the act of congealation a great deal of heat is given out,
and _taken up by the air_, and thus _the severity of the cold is in
some degree moderated_.

164. _Why is it frequently colder when a thaw takes place?_

Because, in the process of thawing, a certain amount of heat is
_withdrawn from the air_, and enters the thawed ice.

165. _What benefit results from these provisions of Nature?_

They moderate both the _severity of frosts_, and _the rapidity of
thaws_, which, in changeable climates, would be seriously detrimental
to _life_, and to _vegetation_.

166. _Why are furs and woollens worn in the winter?_

Because, being non-conductors, they prevent the warmth of the body from
being _taken up by the cold air_.

167. _Why are the skins of animals usually covered with fur, hair,
wool, or feathers?_

Because their coverings, being _non-conductors of heat_, preserve the
warmth of the bodies of the animals.

[Verse: "He sendeth out his word, and melteth them: he causeth his
wind to blow, and the waters to flow."--PSALM CXLVII.]

168. _How is the greater warmth of animals provided for in the winter?_

It is observed that, as winter approaches, there comes a short woolly
or downy growth, which, _adding to the non-conducting property of their
coats_, confines their animal warmth.

     In small birds during winter, let the external colour of the
     feathers be what it may, there will be found a kind of _black_
     down next their bodies. Black is the _warmest colour_, and
     the purpose here is to _keep in the heat_, arising from the
     respiration of the animal.

169. _How is warmth provided for in animals that have no such coats?_

They are furnished with a layer of _fat_, which lies underneath the
skin. Fat consists chiefly of _carbon_, and is a _non-conductor_.

170. _Why are summer breezes said to be cool?_

Because, as they pass over the heated surface of the body, they bear
away a part of its heat.

171. _Why is a still summer air said to be sultry?_

Because, being heated by the sun's rays, _and being a bad conductor_,
it does not relieve the body by _carrying off its heat_.

172. _Why does fanning the face make it feel cooler?_

Because, by inducing currents of air to pass over the face, a part of
the excessive heat is taken up _and carried away_.

173. _Why does perspiration cool the body?_

Because it takes up a part of the heat, and, evaporating, _carries it
into the air_.

174. _Why does blowing upon hot tea cool it?_

Because it directs currents of air over the surface of the tea, and
these currents take up a part of the heat _and bear it away_.

175. _Why does air in motion feel cooler than air that is still?_

Because each wave of air _carries away a certain portion of heat_ and
being followed by another portion of air, _a further amount of heat is
borne away_.

[Verse: "Though I walk in the valley of the shadow of death I will
fear no evil, for thou art with me."--PSALM XXIII.]

176. _Is the atmosphere ever as hot as the human body?_

Not in this country. On the hottest day it is 10 or 12 deg. _cooler
than the temperature of our bodies_.

177. _What is the highest degree of artificial heat which man has been
known to bear?_

A man may be surrounded with air raised to the temperature of 300 deg.
(the boiling point being 212), and yet not have the heat of his body
raised more than two or three degrees above its natural temperature of
from 97 deg. to 100 deg.

178. _Why may man endure this degree of heat for a short time without
injury?_

Because the skin, and the vessels of fat that lie underneath it, are
bad conductors of heat.

And because perspiration passing from the skin and evaporating, would
_bear the heat away_ as fast as it was received.

Because, also, the vital principle (life) exercises a mysterious
influence in the preservation of living bodies from physical influences.

179. _Is the air ever hot enough, in any part of the world, to destroy
life?_

Yes. The hot winds of the Arabian deserts, which are called _simooms_,
scatter death and desolation in their track, withering trees and
shrubs, and burying them under waves of hot sand. When camels see the
approach of a simoom they rush to the nearest tree or bush, or to some
projecting rock, where they place their heads in an opposite direction
to that from which the wind blows, and endeavour to escape its terrible
violence. The traveller throws himself on the ground on the lee side of
the camel, and screens his head from the fiery blast within the folds
of his robe. But frequently both man and beast _fall a prey to the
terrible simoom_.

180. _Why are these hot winds so terrible in their effects?_

Because, being in motion, they search their way to every part of the
body, and passing over it _leave some portion of their heat behind_,
which is again followed by _additional heat from every fresh blast of
wind_.

[Verse: "The fear of the Lord is the beginning of knowledge: but
fools despise wisdom and instruction."--PROVERBS I.]




CHAPTER IX.


181. _What is Radiation?_

The radiation of heat is a _motion of the particles_, in a series of
rays, diverging in every direction from a heated body.

182. _What is this phenomena of Radiation understood to arise from?_

From a strongly repulsive power, possessed by particles of heat, by
which they are excited to recede from each other with great velocity.

183. _What is the greatest source of Radiation?_

The sun, which sends forth rays of _both light and heat_ in all
directions.

184. _When does a body radiate heat?_

When it is surrounded by a medium which is _a bad conductor_.

185. _When we stand before a fire, does the heat reach us by conduction
or by radiation?_

By radiation.

186. _What becomes of the heat that is radiated from one body to
another?_

It is either _absorbed_ by those bodies, or transmitted through
them and passed to other bodies by _conduction_, or diffused by
_convection_, or returned by _reflection_.

187. _How do we know that heat is diffused by radiation?_

If we set a metal plate (or any other body, though metal is best for
the experiment) before the fire, _rays of heat will fall upon it_. If
we turn the plate at a slight angle, and place another object in a
line with it, we shall find that the plate will _reflect the rays it
has received by radiation_, on to the object so placed; but if we place
an object _between the fire and the plate_, we shall find that the
rays of heat _will be intercepted_, and that the latter can no longer
_reflect heat_.

[Verse: "The fear of the Lord is the beginning of wisdom: a good
understanding have all they that do his commandments."--PSALM CXI.]

188. _Does the agitation of the air interfere with the direction of
rays of heat?_

It has been found that the agitation of the air does _not_ affect the
direction of rays of heat.

189. _Why, then, if a current of air passes through a space across
which heat is radiating, does the air become warmer?_

Because it takes up _some portion of the heat_, but it does not alter
the direction of the rays.

     This is clearly illustrated by reference to _rays of light_ which
     are seen under many circumstances. But they are never bent, moved,
     nor in any way affected by the wind.

190. _Why will not a current of air disturb the rays of heat, just as
it would a spider's web, or threads of silk?_

Because heat is an _imponderable_ agent, that is, something which
cannot be acted upon by the ordinary physical agencies. It has _no
weight_, presents no _substantial body_, and is, in these latter
respects, similar to _light and electricity_.

191. _What other sources of radiation of heat are there besides the sun
and the fire?_

The _earth_, and all _minor bodies_, are, in some degree, _radiators of
heat_.

192. _What substances are the best radiators?_

All _rough_ and _dark_ coloured substances and surfaces are the _best
radiators of heat_.

193. _What substances are the worst radiators of heat?_

All _smooth_, _bright_, and _light coloured_ surfaces are _bad
radiators of heat_.

     Dr. Stark, of Edinburgh, has proved, by a series of experiments,
     the influence which the _colours_ of bodies have upon the
     _velocity of radiation_. He surrounded the bulb of a thermometer
     successively with equal weights of _black_, _red_, and _white_
     wool, and placed it in a glass tube, which was heated to the
     temperature of 180 deg. by immersion in hot water. The tube was
     then cooled down to 50 deg. by immersion in cold water; the
     _black_ cooled in 21 minutes, the _red_ in 26 minutes, and the
     _white_ in 27 minutes.

[Verse: "Say unto wisdom, Thou art my sister; and call understanding
thy kinswoman."--PROVERBS VII.]

194. _If you wished to keep water hot for a long time, should you put
it into a bright metal jug, or into a dark earthenware one?_

You should put it into a _bright metal_ jug, because, _being a bad
radiator,_ it would not part readily with the heat of the water.

195. _Why would not the dark earthenware jug keep the water hot as long
as the bright metal one?_

Because the particles of earthenware being rough, and of dark colour,
_they radiate heat freely_, and the water would thereby be quickly
cooled.




CHAPTER X.


196. _But if (as stated in the Lessons upon Conduction) metal is a
better conductor of heat than stone or earthenware, why does not
the metal jug conduct away the heat of the water sooner than the
earthenware jug?_

It would do so, _if it were in contact with another conductor_; but,
being surrounded by air, _which is a bad conductor_, the heat must pass
off _by radiation_, and as bright metal surfaces are bad radiators,
the metal jug would retain the heat of the water _longer than the
earthenware one_.

197. _Supposing a red-hot cannon ball to be suspended by a chain from
the ceiling of a room, how would its heat escape?_

Almost entirely by _radiation_. But if you were to rest upon the
ball a cold bar of iron, a part of the heat would be drawn off by
_conduction_. Warm air would rise from around the ball, and, moving
upwards, would distribute some of the heat by _convection_. And some
of its rays, falling upon a mirror, or any other bright surface, might
be diffused by _reflection_.

[Verse: "I will teach you by the hand of God; that which is with the
Almighty will I not conceal."--JOB XXVII.]

198. _Do some substances absorb heat?_

Yes; those substances which are _the best radiators_ are also _the best
absorbers_ of heat.

199. _Why does scratching a bright metal surface increase its power of
radiation?_

Because every irregularity of the surface acts as a point of radiation,
or _an outlet_ by which the heat escapes.

200. _Why does a bright metal tea-pot produce better tea than a brown
or black earthenware one?_

Because bright metal _radiates but little heat_, therefore the water is
kept hot much longer, _and the strength of the tea is extracted by the
heat_.

201. _But if the earthenware tea-pot were set by the fire, why would it
then make the best tea?_

Because the dark earthenware tea-pot is a good _absorber of heat_, and
the heat it would _absorb_ from the fire would more than counterbalance
the loss by _radiation_.

202. _How would the bright metal tea-pot answer if set upon the hob by
the fire?_

The bright metal tea-pot would probably _absorb less heat_ than it
would radiate. Therefore it would not answer so well, _being set upon
the hob_, as the earthenware tea-pot.

203. _Why should dish covers be plain in form, and have bright
surfaces?_

Because, being bright and smooth, they will not allow heat to escape
_by radiation_.

204. _Why should the bottoms and back parts of kettles and saucepans be
allowed to remain black?_

Because a _thin_ coating of soot acts as a _good absorber of heat_, and
overcomes the _non-absorbing_ quality of the _bright surface_.

[Verse: "And the foolish said unto the wise, Give us of your oil,
for our lamps are gone out."]

205. _But why should soot be prevented from accumulating in flakes at
the bottom and sides of kettles and saucepans?_

Because, although soot is a _good absorber_ of heat, it is a _very bad
conductor_; an accumulation of it, therefore, would cause a waste of
fuel, by _retarding the effects of heat_.

206. _Why should the lids and fronts of kettles and saucepans be kept
bright?_

Because bright metal _will not radiate heat_; therefore, the heat
which is taken up readily through the _absorbing_ and _conducting_
power of the bottom of the vessel, is kept in and economised by the
_non-radiating_ property of the bright top and front.

207. _Does cold radiate as well as heat?_

It was once thought that _cold radiated_ as well as _heat_. But a mass
of ice can only be said to radiate cold, _by its radiating heat in less
abundance than that which is emitted from other bodies surrounding it_.
It is, therefore, _incorrect_ to speak of the _radiation of cold_.




CHAPTER XI.


208. _Why, if you hold a piece of looking-glass at an angle towards the
sum, will light fall upon an object opposite to the looking-glass?_

Because the rays of the sun are _reflected_ by the looking-glass.

209. _Why, when we stand before a mirror, do we see our features
therein?_

Because the rays of light that fall upon us are _reflected_ upon the
bright surface of the mirror.

210. _Why, if a plate of bright metal were held sideways before a fire,
would heat fall upon an object opposite to the plate?_

Because rays of heat may be _reflected_ in the same manner as the rays
of light.

[Verse: "But the wise answered saying, Not so; lest there be not
enough for us and you: but go ye rather to them that sell, and buy for
yourselves."--MATT. XXV.]

211. _Why would not the same effect arise if the plate were of a black
or dark substance?_

Because black and dark substances are not _good reflectors of heat_.

212. _What are the best reflectors of heat?_

Smooth, light-coloured, and highly polished surfaces, especially those
of _metal_.

213. _Why does meat become cooked more thoroughly and quickly when a
tin screen is placed before the fire?_

Because the bright tin reflects the rays of heat back again to the meat.

214. _Why is reflected heat less intense than the primary heat?_

Because it is impossible to collect all the rays, and also because a
portion of the caloric, imparting heat to the rays, is absorbed by
the air, and by the various other bodies with which the rays come in
contact.

215. _Can heat be reflected in any great degree of intensity?_

Yes; to such a degree that inflammable matters may be ignited by it.
If a cannon ball be made red hot, and then be placed in an iron stand
between two bright reflectors, inflammable materials, placed in a
proper position to catch the reflected rays, _will ignite from the
heat_.

     There is a curious and an exceptional fact with reference to
     _reflected_ heat, for which we confess that we are unable to
     give "_The Reason Why_." It is found that snow, which lies near
     the trunks of trees or the base of upright stones, melts before
     that which is at a distance from them, though the sun may shine
     equally upon both. If a blackened card is placed upon ice or snow
     under the sun's rays, the frozen body underneath it will be thawed
     before that which surrounds it. But if we _reflect_ the sun's
     rays from a metal surface, the result is _directly contrary_--the
     exposed snow is the first to melt, leaving the card standing as
     upon a pyramid. Snow _melts_ under heat which is _reflected_ from
     the trees or stones while it withstands the effect of the _direct
     solar rays_. In passing through a cemetery this winter (1857),
     when the snow lay deep, we were struck with the circumstance that
     the snow in front of the head-stones facing the sun was completely
     dissolved, and, in nearly every instance, the space on which the
     snow had melted assumed a coffin-like shape. This forced itself so
     much upon our attention that we remained some time to endeavour
     to analyse the phenomena; and it was not until we remembered the
     curious effect of _reflected heat_ that we could account for it.
     It is obvious that the rays falling from the upper part of the
     head-stone on to the _foot_ of the grave would be less powerful
     than those that radiated from the _centre_ of the stone to the
     centre of the grave. Hence it was that the heat dissolved at the
     foot of the grave only a narrow piece of snow, which widened
     towards the centre, and narrowed again as it approached the foot
     of the head-stone, where the lines of radiation would naturally
     decrease. Such a phenomena would prove sufficient to raise
     superstition in untutored minds.

[Verse: "The light of the righteous rejoiceth, but the lamp of the
wicked shall be put out."--PROVERBS XIII.]

216. _Are good reflectors of heat also good absorbers?_

No; for reflectors at once _send back_ the heat which they receive,
while absorbers _retain it_. It is obvious, therefore, that
_reflectors_ cannot be good _absorbers_.

217. _How do fire-screens contribute to keep rooms cool?_

Because they turn away from the persons in the room rays of heat which
would otherwise make the warmth excessive.

218. _Why are white and light articles of clothing cool?_

Because they _reflect_ the rays of heat.

     White, as a _colour_, is also a bad _absorber_ and _conductor_.

219. _Why is the air often found excessively hot in chalk districts?_

Because the soil _reflects_ upon objects near to it the heat of the
solar rays.

220. _How does the heat of the sun's rays ultimately become diffused?_

It is first _absorbed_ by the earth. Generally speaking, the earth
_absorbs_ heat by day, and _radiates_ it by night. In this way an
equilibrium of temperature is maintained, which we should not otherwise
have the advantage of.

221. _Does not the air derive its heat directly from the sun's rays?_

Only partially. It is estimated that the air absorbs only _one-third_
of the caloric of the sun's rays--that is to say, that a ray of solar
heat, entering our atmosphere at its most attenuated limit (a height
supposed to be about _fifty miles_), would, in passing through the
atmosphere to the earth, part with only one-third of its calorific
element.

[Verse: "As for the earth, out of it cometh bread; and under it is
turned up as it were fire."--JOB XXVIII.]

222. _What becomes of the remaining two-thirds of the solar heat?_

They are _absorbed_ chiefly by the _earth_, the great medium of
calorific _absorption_; but some portions are taken up by _living
things_, both animal and vegetable. When the _rays of heat_ strike upon
the earth's surface, they are passed from particle to particle into the
interior of the earth's crust. Other portions are distributed through
the air and water by _convection_, and a third portion is thrown
back into space by _radiation_. These latter phenomena will be duly
explained as we proceed.

223. _How do we know that heat is absorbed, and conducted into the
internal earth?_

It is found that there is a given depth beneath the surface of the
globe at which an equal temperature prevails. The depth increases as we
travel south or north from the equator, and corresponds with the shape
of the earth's surface, _sinking under the valleys, and rising under
the hills_.

224. _Why may we not understand that this internal heat of the earth
arises, as has been supposed by many philosophers, from internal
combustion?_

Because recent investigations have thrown considerable and satisfactory
light upon the subject. It has been ascertained that the internal
temperature of the earth _increases_ to a certain depth, _one degree in
every fifty feet_. But that below that depth the temperature _begins to
decline_, and continues to do so with every increase of depth.

225. _Do plants absorb heat?_

Yes. They both _absorb_ and _radiate_ heat, under varying
circumstances. The majestic tree, the meek flower, the unpretending
grass, all perform a part in the grand alchemy of nature.

[Verse: "Consider the lilies of the field, how they grow; they toil
not, neither do they spin."]

     When we gaze upon a rose it is not its beauty alone that should
     impress us: every moment of that flower's life is devoted to
     the fulfilment of its part in the grand scheme of the universe.
     It decomposes the rays of solar light, and sends the red rays
     only to our eyes. It absorbs or radiates heat, according to the
     temperature of the ærial mantle that wraps alike the flower and
     the man. It distills the gaseous vapours, and restores to man the
     vital air on which he lives. It takes into its own substance, and
     incorporates with its own frame, the carbon and the hydrogen of
     which man has no immediate need. It drinks the dew-drop or the
     rain-drop, and gives forth its sweet odour as a thanksgiving. And
     when it dies, it preaches eloquently to beauty, pointing to the
     end that is to come!




CHAPTER XII.


226. _How do we know that plants operate upon the solar and atmospheric
heat?_

A delicate thermometer, placed among the leaves and petals of flowers,
will at once establish the fact, not only that flowers and plants have
a temperature differing from that of the external air, but that the
temperature varies in different plants according to the hypothetical,
or supposed requirements, of their existences and conditions.

227. _What is the chief cause of variation in the temperature of
flowers?_

It is generally supposed that their temperature is affected by their
_colours_.

228. _Why is it supposed that the colour of a flower influences its
temperature?_

Because it is found by experiment that the _colours_ of bodies bear an
important relation to their properties respecting _heat_, and hold some
analogy to the relation of _colours_ to _light_.

     If when the ground is covered with snow, pieces of woollen cloth,
     of equal size and thickness, and differing only in colour, are
     laid upon the surface of the snow, near to each other, it will
     be found that the relation of _colour_ to temperature will be as
     follows:--In a few hours the _black_ cloth will have dissolved so
     much of the snow beneath it, as to sink deep below the surface;
     the _blue_ will have proved nearly as warm as the black; the
     _brown_ will have dissolved less of the snow; the _red_ less than
     the brown; and the white the _least_, or none at all. Similar
     experiments may be tried with reference to the _condensation
     of dew_, &c. And it will be uniformly found that the _colour_
     of a body materially affects its powers of _absorption_ and of
     _radiation_.

[Verse: "And yet I say unto you, that even Solomon, in all his
glory, was not arrayed like one of these."--MATT. VI.]

229. _Why do we know that these effects are not the result of light?_

Because they would occur, in just the same order, in the absence of
light.

230. _Why are dark coloured dresses usually worn in winter, and light
in summer?_

Because black _absorbs_ heat, and therefore becomes warm; while _light
colours_ do _not_ absorb heat in the same degree, and therefore they
remain cool.

231. _Why do iron articles, even when near fire, usually feel cool?_

Because they are bad absorbers, and do not take up heat freely, unless
they are _in contact_ with a hot body.

232. _How is heat diffused through the atmosphere?_

By _convection_. The warmth radiating from the surface of the earth
warms the air in contact with it; the air expands, and becoming
lighter, flies upwards, bearing with it the caloric which it holds, and
diffusing it in its course.

233. _How do the waters of the ocean become heated?_

Chiefly by _convection_. Nearly all the heat which the sun sheds
upon the ocean is borne away from its surface by evaporation, or is
radiated back into the atmosphere. But the ocean gathers its heat by
_convection_ from the earth. It girdles the shores of tropical lands
where, being warmed to a high degree of temperature, it sets across the
Atlantic from the Gulf of Mexico, and exercises an important influence
upon the temperature of our latitude.

234. _What is the cause of winds?_

Currents of air, and winds, are the result of _convection_. The air,
heated by the high temperature of the tropics, _ascends_, while the
colder air of the temperate and the frigid zones _blows towards the
equator_ to supply its place.

[Verse: "Give unto the Lord the glory due unto his name; worship the
Lord in the beauty of holiness."--PSALM XXIX.]

235. _What is the cause of sea breezes?_

Sea breezes are also the result of _convection_. The land, under the
heat of the day's sunshine, becomes of a high temperature, and the
expanded air on its surface _flies away towards the ocean_. As the sun
goes down, the earth cools again, and the air _flies back_ to find its
equilibrium.

     Many countries by the sea are subjected to these periodical
     breezes, known as either "land" or "sea breezes," according to
     their direction. About eight o'clock in the morning an ærial
     current begins to flow from the sea towards the land, and
     continues until about three o'clock in the day; then the current
     takes a reverse direction, flowing from the land to the sea.
     This it continues to do throughout the night, until the time of
     sunrise, when a temporary calm ensues.

236. _Why does a soap bubble ascend in the air?_

Because, being filled with _warm_ air, it is _lighter_ than the
surrounding medium, and therefore ascends.

237. _Why does the bubble fall after it has been in the air some time?_

Because the air contained in it has become cool, and, as it contains
carbonic acid gas, it is _heavier_ than the air.

238. _What became of the warmth at first contained in the bubble?_

It has been _distributed in the air_ through which the bubble passed.

239. _What does this simple illustration of the distribution of warmth
explain?_

It explains the law of _convection_, or _heat distribution_, over the
surface of the globe.

240. _Why does air ascend the chimney?_

Because, being heated, it becomes _lighter_ than the surrounding
medium, and therefore flies upwards, through the outlet provided for it.

241. _Why does air fly from the doors and windows towards the
fire-place?_

Because, as the warm air flies away, cold air rushes in to occupy its
place.

[Verse: "How much better is it to get wisdom than gold? and to get
understanding rather to be chosen than silver."--PROVERBS XVI.]

242. _What does this example of the motion of the air in our rooms
explain?_

It explains the movement of volumes of air by _convection_, and
illustrates the origin of _breezes_ and _winds_.

243. _What is the chief effect of this law of convection?_

Under its influence air and water are the great _equalisers of solar
heat_, rendering the earth agreeable to living things, and suited to
the laws of their existence.

Owing, also, to this law of _convection_, the constituents of the air
are equalised. The breath of life, supplied by the purer oxygen of the
"sunny south," is diffused in salubrious gales over the wintry climes
of the north. And the waters, evaporated from the bosom of the central
Atlantic Ocean and the Pacific, are borne across vast continents, and
poured down in fertilising showers upon distant lands.

     To the educated mind, nothing is too simple to merit attention.
     To the ignorant, few things are sufficiently attractive to excite
     curiosity. Knowledge enables us to estimate the varied phenomena
     that are hourly arising around us, and to see, even in the
     most trifling effects, illustrations of those great causes and
     consequences that govern with mighty power the material world.
     Man, sitting by his fire-side, is enabled to witness the operation
     of some of nature's grandest laws: _light_ and _heat_ are around
     him; _conduction_, _radiation_, _reflection_, _absorption_,
     and _convection_ of heat are all going on before him; little
     winds are sweeping by his footstool, and warm currents, with
     miniature clouds folded in their arms, are passing upward before
     his view. Chemical changes are going on; the solid rock of coal
     disappears, flying away as an invisible gas. The little "hills are
     melted," and hard stones have been converted into "fervent heat."
     Although some of these changes are imperceptible to the _eye_,
     they are manifest to the educated _mind_; and the pleasures of
     philosophical observation are as sweet as a poet's dreams.




CHAPTER XIII.


244. _Why will a piece of paper, held three or four inches over the
flame of a candle, become scorched?_

[Verse: "Neither do men light a candle, and put it under a bushel,
but on a candlestick; and it giveth light unto all that are in the
house."--MATT. V.]

Because the hot air and gas produced by the burning of the candle
_ascends_ rapidly.

245. _Why will a piece of paper held about an inch below the flame of a
candle scarcely become warmed?_

Because the heat _ascends_; and only a little of it falls upon the
paper, and that by _radiation_.

[Illustration: Fig. 2.--DIAGRAM SHOWING THE COMBUSTION OF A CANDLE.]

246. _Why does the lower part of the flame of a candle_ (D) _burn of a
blue colour?_

Because the _hydrogen_ of the tallow, having a stronger affinity for
the _oxygen_ of the air than _carbon_ has, ignites first. Pure hydrogen
burns with a bluish flame.

247. _Why does the middle of the flame_ (C) _look dark?_

Because it is occupied with gaseous vapours, derived from the tallow,
which have not yet _ignited_.

248. _Why does the upper part of the flame_ (B) _produce a bright
yellow light?_

Because it is in this part of the flame that the _hydrogen_ of
the candle, and the _oxygen_ of the air, combine, and there is
just sufficient _carbon_ mixed with the _hydrogen_ to improve its
_illuminating power_.

249. _Why is there a fringe of pale light_ (A) _around the upper part
of the flame?_

Because some of the _carbon_ escapes in a state of _incandesence_, and
as soon as it reaches the air it combines with _oxygen_, and so forms
_carbonic acid gas_.

     If any dark body, such as the blade of a knife, be held between
     the eye and the flame of the candle, so as to shut off the light
     of the more luminous part, the pale fringe around the flame will
     be found distinctly perceptible. _Incandesence_ means _heated to
     whiteness_.

[Verse: "How oft is the candle of the wicked put out? and how oft
cometh their destruction upon them?"--JOB XXI.]

250. _Why does the flame terminate in a point?_

Because cold air rushes towards the flame in every direction, and
is carried upward. At the point where the flame terminates the cold
currents have so _reduced the temperature_ that combustion can no
longer be sustained.

251. _Why, if you hold anything immediately over the flame, will the
flame lengthen?_

Because, by preventing the rapid escape of the heated air, you maintain
a temperature which _increases the combustion_ at the point of the
flame.

252. _Why should persons whose clothes take fire, throw themselves
down?_

Because flame spreads most rapidly in an _upward_ direction.

253. _Why should persons whose clothes are on fire roll slowly about
when they are down?_

Because they thereby _press out_ the fire.

254. _Why does pressing a flame or a spark put it out?_

Because it prevents the contact of the flame or spark with the _oxygen_
of the air.

     Extinguishers put out the flame of candles in the same manner. A
     person dies from "suffocation" through the absence of oxygen; and
     it is literally practicable to _"suffocate" a fire_.

255. _Why does the wick turn black as it burns?_

Because it consists principally of _carbon_.

256. _Why, when the point of the wick turns out and meets the air, does
it exhibit a bright spark?_

Because the _carbon_ of the wick comes into immediate contact with the
_oxygen_ of the air.

257. _Why does holding a candle "upside down" put it out?_

Because the melted grease runs down too rapidly, and at too low a
temperature to undergo combustion. It therefore _reduces the heat_, and
extinguishes the flame.

[Verse: "Lord, what is man that thou takest knowledge of him! or the
son of man, that thou makest account of him."--PSALMS CXLIV.]

258. _Why is it more difficult to blow out the flame of a candle with a
cotton wick than one with a rush wick?_

Because the cotton wick imbibes more of the combustible materials, and
holds in its loose texture the inflammable gases in a state ready for
combustion.

259. _Why does blowing sharply at a candle flame put it out?_

Because the breath drives away the vapour of the grease which, becoming
gaseous, supports the flame.

And because too rapid a flow of cold air reduces the temperature below
the point at which combustion can be maintained.

260. _Why will a gentle puff of breath, if given speedily after the
flame is extinguished, rekindle it?_

Because the _oxygen_ of the air combines with the _carbon_ and
_hydrogen_ that are still escaping from the _heated wick_, and
re-lights it.

261. _Why will not a similar puff rekindle the flame of a rushlight?_

Because its wick retains but _little heat_, and holds a comparatively
small amount of combustible matter in a _volatile state_.

262. _Why is a fire, when it is very low, sometimes put out by blowing
it?_

Because the too rapid flow of cold air _reduces the temperature_ of the
burning mass.

263. _Why will a piece of paper twisted like an extinguisher put out a
candle?_

Because, before the flame of the candle can ignite the paper, _the
oxygen contained within it is consumed_, and the flame is suffocated.

[Verse: "When his candle shined upon my head, and when by his light
I walked through darkness."--JOB XXIX.]

264. _Why do tallow candles require snuffing?_

Because the _oxygen_ of the air cannot reach the wick through the body
of flame--therefore the _unconsumed carbon_ accumulates upon the wick.

265. _Why do composite and wax candles not require snuffing?_

Because their wicks are made by a series of plaits, by which they are
bent to meet the _oxygen_ of the air, and consumed.

266. _Why does setting a glass upon a lamp increase its brilliancy,
though it shortens the flame?_

Because it conducts an increase of air to the flame, and the greater
supply of _oxygen_ causes the escaping vapour of oil to be all rapidly
consumed.

267. _Why does a candle burn dimly when the wick has become loaded with
carbon?_

Because the carbon _radiates_ the heat, and disperses it, and reduces
the heat of the flame below that temperature which is essential to its
_luminosity_.

268. _What differences characterise the combustion of carbon and of
hydrogen?_

The combustion of _carbon_ takes place without the production of flame.
The charcoal (or carbon in any other form) being heated to redness,
enters directly into combination with the _oxygen_ of the surrounding
air, and the carbonic acid gas, being invisible, passes away unobserved.

But in the combustion of _hydrogen_ the heat developed is so intense as
to render _the gas itself luminous_, just as iron may be heated to a
red or white heat.

269. _What has become of the candle when it has been burnt?_

It has been resolved partly into _carbonic acid gas_ which, though
unperceived, has diffused itself through the surrounding air; and
partly into _water_, which escaped in the form of thin vapour.

270. _Has any part of the candle been consumed or lost?_

No; there is no such thing as "loss" in the operations of nature. Every
particle of the candle, now invisible, exists either in the form of
_gas_, _vapour_, or _water_, with, perhaps, a few solid particles that
may be called _ashes_, but which are too minute to excite attention.

[Verse: "I know that whatsoever God doeth, it shall be for ever:
nothing can be put to it, nor anything taken from it; and God doeth it
that men should fear before him."--ECCLES. III.]

     The economy of nature should teach us a very impressive
     lesson--_nothing is suffered to be wasted_, not even the slightest
     atom. As soon as any body has fulfilled its purpose in one state
     of being, it is passed on to another. The candle, existing no
     longer as a candle, is flying upon the wings of the air as
     _carbonic acid gas_, and as _water_. These probably find their
     way to the garden or the field, where the carbonic acid gas forms
     the _food of the plant_, and the water affords it a refreshing
     _drink_. And can it be supposed that the Almighty Being, who has
     thus economised the existence of the _material_ creation, should
     be less mindful of the immaterial _soul_ of man? There _is_ an
     eternity before us, the certainty of which is evidenced even by
     the laws of the material creation.




CHAPTER XIV.


271. _What is coal?_

Coal is a "_vegetable fossil_."

272. _What is meant by a vegetable fossil?_

It is a substance _originally vegetable_, which, by pressure and other
agencies within the earth, has been brought to a condition approaching
that of _mineral_ or earthy matter.

273. _Why do we know that coal is of vegetable origin?_

By the _chemical components_ of its substance; and also by the
_vegetable forms_ that are found abundantly in coal beds.

     Professor Buckland, in his _Bridgewater Treatise_, speaking of
     the impressions of plants found in the coal mines, says; "The
     finest example I have ever witnessed is that of the coal mines
     of Bohemia. The most elaborate imitations of living foliage upon
     the painted ceilings of Italian palaces bear no comparison with
     the beauteous profusion of extinct vegetable forms with which
     the galleries of these instructive coal mines are overhung.
     The roof is covered as with a canopy of gorgeous tapestry,
     enriched with festoons of most graceful foliage, flung in wild
     irregular profusion over every part of its surface. The effect
     is heightened by the contrast of the coal-black colour of these
     vegetables with the light ground-work of the rock to which they
     are attached. The spectator feels himself transported, as if by
     enchantment, into the forests of another world; he beholds trees,
     of forms and characters now unknown upon the surface of the
     earth, presented to his senses almost in the beauty and vigour of
     their primeval life; their scaly stems and bending branches, with
     their delicate apparatus of foliage, are all spread forth before
     him, little impaired by the lapse of countless ages, and bearing
     faithful records of extinct systems of vegetation which began
     and terminated in times of which these relics are the infallible
     historians."

[Verse: "Surely every man walketh in a vain show; surely they are
disquieted in vain: he heapeth up riches, and knoweth not who shall
gather them."--PS. XXXIX.]

274. _What are the chemical components of coal?_

They consist of _carbon_, _hydrogen_, _oxygen_, and _nitrogen_. The
proportions of these elements vary in different kinds of coal. Carbon
is the chief component; and the proportions may be stated to be,
generally, _carbon_, 90 per cent.; _hydrogen_, from 3 to 6 per cent.;
the other elements enter into the compound in such small proportions,
that, for all ordinary purposes, it is sufficient to say that coal
consists of _carbon_ and _hydrogen_, but chiefly of _carbon_.

275. _What is charcoal?_

Charcoal consists almost entirely of _carbon_. It is made from _wood_
by the application of heat, without the admission of air. The hydrogen
and oxygen of the wood are expelled, and that which remains is
charcoal, or _carbon_ in one of its purest states.

276. _What is animal charcoal?_

Animal charcoal, like vegetable charcoal, consists of _carbon_ in a
state approaching purity. It is made from the _bones of animals_,
heated in iron cylinders. It is commonly called _ivory black_.

277. _What is the purest form of carbon known?_

The purest form of _carbon_ is the _diamond_, which may be said to be
absolutely pure.

     Hence we derive another of the beautiful lessons of science--a
     lesson which teaches us to _despise nothing that God has given_.
     The soot which blackens the face of a chimney-sweep, and the
     diamond that glistens in the crown of the monarch, consist of the
     same element in merely a different atomic condition. What a lesson
     of humility this teaches to Pride! The haughty beauty as she walks
     the ball-room, inwardly proud of the radiance of her gems as they
     rise and fall upon her breast, little thinks or knows that _every
     breath that is expired around her wafts away the like element of
     which her treasures are composed_. That even in our own flesh and
     bones the same abounding substance lies hid; and that the buried
     tree of the primitive world, and the little flower of to-day, are
     both the instruments of giving this singular element to man!

278. _What is coke?_

Coke is coal, divested of its hydrogen and other volatile parts, by
a similar process to that by which charcoal is produced. It forms the
residue after hydrogen gas has been made from coals. It consists almost
entirely of _carbon_.

[Verse: "Oh that men would praise the Lord for his goodness, and for
his wonderful works to the children of men."--PSALM CVII.]

279. _Why do burning coals produce yellow flame?_

Because the _hydrogen_ which they contain is combined with some
proportion of _carbon_, which imparts a bright yellow colour to the
flames.

280. _Why do some of the flames of a fire appear much whiter than
others?_

Because the quality of coals, and the conditions under which they are
burnt, are liable to variation. Some coals yield a _heavy_ hydrogen,
called _bi-carburetted hydrogen_, which burns with a much brighter
flame than _carburetted hydrogen_.

281. _Why does bi-carburetted hydrogen burn with a whiter flame than
the common coal gas?_

Because it is combined with a larger proportion of _carbon_, to which
it owes its increased luminosity.

282. _Why do some of the flames of a fire appear blue?_

Because the hydrogen which is escaping where those flames occur is
_pure hydrogen_, destitute of carbon.

283. _Why does the fire sometimes appear red, and without flame?_

Because the volatile gases have been driven off and consumed, and
combustion is continued by the _carbon_ of the coals and the _oxygen_
of the air.

284. _What effect has the burning of a fire upon the composition of the
air?_

It is found that in burning 10lb. of coal the oxygen contained in 1,551
cubic feet of air is altogether absorbed. It is therefore necessary to
keep the atmosphere of a room, in which a coal fire is burning, fresh
and pure, to supply 155 cubic feet of fresh air for every pound of coal
that is consumed.

[Verse: "O Lord how manifold are thy works, in wisdom hast thou made
them all: the earth is full of thy riches."--PSALM CIV.]

285. _Why does wood which is "green" hiss and steam when it is burnt?_

Because it contains a large amount of water, which must be evaporated
before combustion can proceed.

286. _What is the effect of this evaporation?_

A great deal of heat is unprofitably expended in driving off the water
of the fuel.

287. _Why does poking a fire cause it to burn more brightly?_

Because it opens avenues through which the air may enter to supply
_oxygen_.

288. _Why do "blowers" improve the draft of air through a fire?_

Because, by obstructing the passage of the current of air _over_ the
fire, they cause additional air to pass _through_ it, and therefore a
greater amount of _oxygen_ is carried to the coals.

289. _What is smoke?_

Unconsumed particles of _coal_, rendered volatile by heat, and driven
off.

290. _What is soot?_

_Carbon_ in minute particles, driven off with other volatile matters
and deposited on the walls of chimneys.

291. _Why do fresh coals increase the quantity of smoke?_

Because they contain volatile matters which are easily driven off; and
because, also, they reduce momentarily the heat, so that those matters
that first escape cannot be consumed.

292. _Why do charcoal and coke fires burn clearly and without flame?_

Because the _hydrogen_ has been previously driven off from those
substances.

293. _Why is it difficult to light charcoal and coke fires?_

Because they contain no _hydrogen_ to produce _flame_, and assist
combustion.

[Verse: "He hath made his wonderful works to be remembered: the Lord
is precious and full of compassion."--PSALM CXL.]

     A new plan of kindling fires has lately been recommended. Coals
     are to be laid in the _bottom_ of the fire-place to a considerable
     depth, then the paper and wood are to be laid on, and then a
     little coals and cinders over them. This plan of "laying in" the
     fire is precisely the _reverse_ of that which has been pursued
     for many years. The theory is, that when the coals in the bottom
     are ignited, a more even combustion is kept up, whilst the smoke
     and gas which would otherwise escape, and become as so much waste
     fuel, is burnt up, and produces heat. We have heard the plan
     strongly recommended by persons who have tried it, and who testify
     to the great economy of fuel to which it conduces.




CHAPTER XV.


294. _Why does paper ignite more readily than wood?_

Because its texture is less _dense_ than that of wood; its particles
are therefore more _readily heated_ and decomposed.

295. _But if articles of loose texture are bad conductors of heat, why
do they so easily ignite?_

The fact that they are _bad conductors_ assists their ignition. The
heat which would pass from particle to particle of the dense substance
of iron, and be _conducted away_, accumulates in the interspaces of
paper, and ignites it.

296. _Why does wood ignite less readily than paper?_

Because its substance is _denser_ than that of paper; it therefore
requires a higher degree of heat to inflame its substance.

297. _Why does wood, when ignited, burn longer than paper?_

Because, being a denser substance, it submits a _larger number of
particles_, within a given space, to the action of the heat, and the
formation of gases.

298. _Why do we, in lighting a fire, first lay in paper, then wood, and
lastly coals?_

Because the paper is more easily ignited than wood, and wood than
coals; therefore the _paper_ assists the ignition of the _wood_, and
the _wood_ assists the ignition of the _coals_.

[Verse: "It is a good thing to give thanks unto the Lord, and to
sing praises unto thy name, O Most High."--PSALM XCII.]

299. _Why will not wood ignite by the flame of a match?_

It will do so, unless there is a great disproportion between the size
of the wood and the flame of a match. A _thin_ piece of wood will
ignite, but a square block will not, because the heat of the flame is
insufficient to raise the temperature of a _large surface_ to the point
that will drive out its gases.

300. _Why do we place the paper under the wood, and the wood under the
coals?_

Because heat and flame, when surrounded by air, have a strong tendency
to spread themselves _upwards_.

301. _Would it be possible to light the coals by putting the paper and
the wood upon the top?_

It would be possible; but the loss of heat would be so great, that a
_much larger quantity_ of paper and wood would be required.

302. _Why does a poker laid across the top of a dull fire revive it?_

Because the poker _radiates_ the heat it receives from the fire
downward upon the fuel.

Because, also, it divides the ascending air, and thereby _creates
currents_.

     The amount of good which the poker does to the fire is very slight
     indeed. Generally, the housewife stirs the fire first, and blows
     or brushes away the ashes that prevent the influx of air. She then
     places the poker upon the top, and the popular mind supposes that
     the poker "draws" the fire. The custom of placing a poker over
     the fire is of very remote antiquity. It was once believed that
     forming _a cross_, by placing the poker over the bars, protected
     the fire from the hostility of malignant _witches_!

303. _Why should fire-places be fixed as low as possible in rooms?_

Because heat _ascends_, and when the fire-places are high the lower
parts of the room are _inadequately warmed_.

Also, as currents of air fly towards the fire, elevated fire-places
_cause drafts_ about the persons of the inmates to a much greater
extent than they would if they were lower down.

[Verse: "Unto thee, O God, do we give thanks: for that thy name is
near thy wondrous works declare."--PSALM LXXV.]

304. _Why, if a piece of paper be laid with its flat surface upon the
fire, will it "char," but not ignite?_

Because, as in the case of the proper candle-extinguisher, the
_carbonic acid gas_ accumulating beneath it prevents its igniting.

305. _Why, if you direct a current of air towards the paper, will it
burst into a blaze?_

Because the carbonic acid gas is displaced by a current of air
containing _oxygen_.

306. _Why does water extinguish fire?_

Because it _saturates the fuel_, and prevents the gases thereof from
combining with the oxygen of the air.

307. _As water contains oxygen, why does not the oxygen of the water
support the fire?_

Because the affinity between the _hydrogen_ and _oxygen_ of the water
is so strong that fire cannot separate them.

     Water may be decomposed by _heat_, as will be hereafter explained.
     But the heat of an ordinary fire is insufficient. There is,
     however, some reason for believing that, in cases of very large
     fires, such as the accidental burning of houses, &c., when the
     supply of water thrown upon the fire is very deficient, the water
     _does_ become _decomposed_, and add to the fury of the flames.

308. _Why does the blacksmith sprinkle water upon the coals of his
forge?_

The blacksmith uses _small coals_ because the small pieces thereof are
more easily ignited than large lumps would be, and they convey heat
better by completely surrounding the articles put into the fire. He
sprinkles water on the coal dust _to hold its particles together by
cohesion_, until the heat forms it into a cake. A strong blast of hot
hair drives the vapour of the water away, and leaves a porous mass to
the action of the fire.

309. _Why, when the blacksmith thrusts a heated iron into a tankard of
water, do we recognise a peculiar smell?_

Because the intense heat disengages a small volume of the gases of
which water is formed.

[Verse: "Oh the depth of the riches both of the wisdom and knowledge
of God! how unsearchable are his judgments, and his ways past finding
out."--ROM. XI.]

310. _Which gas do we (in this instance) recognise by the smell?_

The _hydrogen_ gas. Oxygen gas possesses no odour.

311. _What is Spontaneous Combustion?_

Spontaneous combustion is that which occurs in various bodies when they
become highly heated by _chemical changes_.

312. _Why is heat developed during chemical changes?_

Because, as all bodies contain _latent caloric_, the disturbance of the
atoms of which those bodies are composed, during the new combinations
that constitute _chemical changes_, frequently sets the caloric free,
and an _accumulation of caloric_ produces spontaneous combustion.

313. _Does a match ignite spontaneously when drawn over a rough
surface?_

No. Because in this case the combustion arises from heat _applied by
friction_.

314. _Does phosphorous ignite spontaneously when held in a warm hand?_

Phosphorous will ignite when held in a warm hand, but it does not then
produce spontaneous combustion, because it ignites through the agency
of _applied heat_.

315. _But if a piece of dry phosphorous be sprinkled with powdered
charcoal it will ignite, without the application of heat. Why is this?_

Because the _carbon_ (charcoal) absorbs _oxygen_ from the air, and
conveys it to the _phosphorous_. Here are _chemical changes_ which
develope heat, and produce _spontaneous combustion_.

316. _Why do hay-stacks sometimes take fire?_

Because the hay, having become damp, decays, and passes on to a state
of _fermentation_, in which _chemical changes occur_, during which
heat is evolved. Hay, taking fire under these circumstances, would
exhibit _spontaneous combustion_.

[Verse: "Who hath woe? who hath sorrow? who hath contentions? who
hath babbling? who hath words without cause? who hath redness of the
eyes? * * * They that tarry long at the wine."--PROV. XXIII.]

317. _What substances are liable to produce spontaneous combustion?_

All substances which contain sugar, starch, and other components
liable to _fermentation_. All bodies that evolve, under low degrees of
temperature, _inflammable gases_. And all organic bodies undergoing
decay.

     Grain, cotton, hemp, flax, coals, oily and greasy substances.

318. _What is the Ignis Fatuus (sometimes called "Will-o'-the-Wisp",
"Corpse Candles," and "Jack-o'-Lantern")?_

It is a flame produced by spontaneous combustion, caused by the decay
of animal or vegetable bodies, which evolve _phosphoretted hydrogen_
gas, under circumstances attended by a low degree of heat, sufficient
to ignite the gases. It is mostly seen over marshy places, and
burial-grounds.

     Many a "Ghost Story" has owed its origin to these singular but
     harmless appearances. People, ignorant of the cause, have been
     terrified at the effect. To the fancy of an affrighted mortal,
     the simple flame of the _Ignis Fatuus_ has assumed the form of
     a departed friend, and even found a supernatural voice. If,
     excited by a momentary daring, the beholder moved towards the
     light upon which he gazed, it fled from him. If he turned from
     it and walked away, it followed him, step by step. The darkness
     of a lonely road, or the sacred solitude of a burial-place, have
     been sufficient accessories to authenticate the appearance of a
     spirit. And yet how simple the phenomenon? Matters so volatile as
     those which produce the _Ignis Fatuus_ would naturally be driven
     back by the motion in the air caused by an advancing body; and, on
     the other hand, a body moving from them would create a current in
     which the _Ignis Fatuus_ would follow. Poisonous gases, escaping
     from decaying bodies, pass into the air and take fire. They are
     thereby converted into harmless compounds. Thus we see that the
     "ghost" which terrifies the mind of the ignorant, becomes a
     "guardian angel" to the educated.

319. _Has spontaneous combustion ever occurred in living bodies?_

It has occurred in numerous instances to persons habituated to the
excessive use of spirits.

320. _Why should spontaneous combustion occur in the case of the
drunkard?_

Because spirituous drinks contain a large proportion of ALCOHOL, one
of the constituents of which is _hydrogen_. The vital energies of
the drunkard, being destroyed by excess, chemical agencies obtain an
ascendancy, and it is supposed that the _hydrogen_ of the alcohol
combines with the _phosphorous_ of the body to form _phosphoretted
hydrogen_, which ignites spontaneously, and literally consumes the
living temple.

[Verse: "Drought and heat consume the snow waters; so doth the grave
those which have sinned."--JOB XXIV.]

     Cases of spontaneous combustion are of rare occurrence. But they
     are sufficiently well authenticated by high medical authority,
     in many parts of the world, to present an awful warning to
     the inveterate drunkard. The cases of which we have read the
     particulars present details of the most appalling description. How
     signally the Almighty displeasure at intemperance is expressed,
     when the very drink which imparts the mad pleasure of intoxication
     is made the _direct_ instrument by which the drunkard is destroyed!




CHAPTER XVI.


321. _Why does friction produce heat?_

Because all bodies contain _latent heat_, that is, heat that lies hid
in their substance, and the rubbings of two bodies against each other
_draws the latent heat to the excited surfaces_.

322. _Why does the rubbing of two surfaces together attract latent heat
to those surfaces?_

Because it is a law of nature that _heat_ shall always attend _motion_;
and it is generally found that the _intensity of heat_ bears a specific
relation to the _velocity of motion_.

323. _What are the sources of heat?_

The _rays_ of the _sun_, the _currents_ of _electricity_, the _action_
of _chemicals_, and the _motion_ of _substances_.

324. _Why does water freeze?_

Because its latent heat is partly _drawn off_ by the surrounding air.

325. _Why does ice melt?_

Because the heat, once latent in the water, but drawn off by the air,
_has returned_ to it, and restored the water to its former condition.

[Verse: "So teach us to number our days, that we may apply our
hearts unto wisdom." PSALM XC.]

326. _Why does water become steam?_

Because a larger amount of heat has entered into it than can remain
latent in water. The water therefore expands and rises in the form of
vapour, or _water attenuated by heat_.

327. _How many degrees of heat are latent, or hidden, in the different
states of water?_

In thawing _ice_, 140 deg. of caloric become latent; and in converting
the water into steam, 1,000 deg. more of caloric are be taken up.
Therefore, _ice_ requires to take up 1,140 deg. of latent caloric
before it becomes steam.

328. _What is the most modern theory of heat?_

It is this--that caloric, which produces heat, is an extremely _subtile
fluid_, of so refined a nature that it possesses no weight, yet is
capable of diffusing itself among the particles of the most solid
bodies.

It is also believed that--all bodies are subject to the action of two
opposing forces: one, the _mutual attraction_ of their _particles_; the
other, the _repulsive force_ of _caloric_--and that bodies exist in the
_æriform_, _fluid_, or _solid state_, _according to the predominance of
either the one or the other of these opposing forces_.

329. _How do we measure the quantity of caloric in any substance?_

It is impossible to determine the amount of caloric which any body
contains. Our _sensations_ would obviously be deceptive, since, if we
dipped the right hand in snow, and held the left hand before the fire,
and then immersed both hands in cold water, the water would feel _warm_
to the _right hand_ and _cold_ to the _left hand_.

But, as _caloric_ uniformly expands substances that are under its
influence, one of the bodies most sensitive to _calorific_ effects
has been selected to be the _indicator_ of the amount of _caloric_.
This substance is _quicksilver_; and the scale of measurement, and
the apparatus for exhibiting the rise or fall of the quicksilver,
constitute the _thermometer_.

330. _If it is impossible to measure the amount of caloric in any
substance, how can it be said that ice absorbs_ 140 _deg. in becoming
water?_

Those figures simply record the amount of calorie indicated by the
_thermometer_. The instrument will show with sufficient accuracy
the _relative amount_ of caloric in various bodies, or in the same
bodies _under different circumstances_, but it can never determine the
_precise amount of caloric_ in any one body.

[Verse: "Great is the Lord, and greatly to be praised in the city of
our God, in the mountain of his holiness."--PSALM XLVIII.]

331. _Why, if a hot and a cold body were placed near to each other,
would the cold one become warmer, and the hot one cooler?_

Because _free caloric_ (that is, caloric that is not latent,) always
exhibits a tendency to establish an _equilibrium_. If twenty bodies, of
different temperatures, were placed in the same atmosphere, they would
_all soon arrive at the same temperature_. The caloric would leave the
bodies of those of the _highest_, and find its way to those of the
_lowest_ temperature.

332. _How does caloric travel?_

It travels in _parallel rays_ in all directions with a velocity
approximating to that of light; and it passes through various bodies
with a rapidity proportionate to their power of _conduction_.

333. _Why does melted metal run like a stream of fluid?_

Because _caloric_ has passed into its substance, and, repelling its
particles, has separated them to that degree which produces fluidity.

334. _How do we know that it is caloric passing into the substance of
the metal which produces this effect?_

Because, as soon as a bar of metal begins to be heated, it _expands_
and _lengthens_. It continues to do so, until the heat arrives at that
point which _causes the metal to melt_.

335. _Why does the iron of an ironing-box sometimes become too large
for the box to receive it?_

Because _caloric_ has passed into the substance of the iron, and
_repelled its particles_, by which it has become expanded.

336. _Why does the iron enter the box when it has become partially
cooled?_

Because a portion of the caloric has left the iron, the particles of
which have _drawn closer together_, and contracted the mass.

[Verse: "Cast thy burden upon the Lord, and he shall sustain thee;
he shall never suffer the righteous to be moved."--PSALM LV.]

     This effect is frequently observed by females in domestic life,
     who, when they are ironing, or using the Italian irons, find that
     the heated metal has been too much expanded to enter the box or
     tube. They find it necessary to wait until the cooling of the iron
     has had the effect of reducing its dimensions. The expansion of
     bodies by heat is one of the grandest and most important laws of
     nature. We are indebted to it for some of the most beautiful, as
     well as the most awful, phenomena. And science has gained some of
     its mightiest conquests through its aid. Yet frequently, though
     quite unthought of, in the hands of the humble laundress, will
     be found a most striking illustration of this wonderful force of
     caloric.

337. _Are there any instances in which the abstraction of latent heat
will reduce the hulk of bodies?_

Yes, there are several. But the most familiar one is that which is
exhibited by mixing a _pint_ of the _oil of vitriol_ with a _pint_ of
_water_. _A considerable amount of heat will be evolved_; and it will
be found that the two pints of fluid _will not afterwards fill a quart
measure_.

338. _Is there any latent heat in air?_

Yes: a considerable amount. In a pint measure of air, though in no way
evident to our perceptions, there lurks sufficient caloric to raise a
piece of metal several inches square to glowing redness.

339. _How do we know that caloric exists in the air?_

It has been positively demonstrated by the invention of a small
condensing syringe, by which, through the rapid compression of a small
volume of air, a spark is emitted which ignites a piece of prepared
tinder.

340. _What is the cause of the spark when a horse's shoe strikes
against a stone?_

The _latent heat_ of the iron or the stone is set free by the _violent
percussion_. The same effect takes place when _flint_ strikes against
_steel_, as in the old method of obtaining a light with the aid of the
tinder-box.

[Verse: "The waters are laid as with a stone, and the face of the
deep is frozen."--JOB XXXVIII.]

     What an eloquent lecture might be delivered upon the old-fashioned
     tinder-box, illustrated by the one experiment of "striking a
     light." In that box lie, cold and motionless, the Flint and Steel,
     rude in form and crude in substance. And yet, within the breast of
     each, there lies a spark of that grand element which influences
     every atom of the universe; a spark which could invoke the fierce
     agents of destruction to wrap their blasting flames around a
     stately forest, or a crowded city, and sweep it from the face of
     the world; or which might kindle the genial blaze upon the homely
     hearth, and shed a radiant glow upon a group of smiling faces; a
     spark such as that which rises with the curling smoke from the
     village blackmith's forge--or that which leaps with terrific wrath
     from the troubled breast of a Vesuvius. And then the tinder--the
     cotton--the carbon: What a tale might be told of the cotton-field
     where it grew, of the black slave who plucked it, of the white
     toiler who spun it into a garment, and of the village beauty who
     wore it--until, faded and despised, it was cast amongst a heap of
     old rags, and finally found its way to the tinder-box. Then the
     Tinder might tell of its hopes; how, though now a blackened mass,
     soiling everything that touched it, it would soon be wedded to
     one of the great ministers of nature, and fly away on transparent
     wings, until, resting upon some Alpine tree, it would make its
     home among the green leaves, and for a while live in freshness
     and beauty, looking down upon the peaceful vale. Then the Steel
     might tell its story, how for centuries it lay in the deep caverns
     of the earth, until man, with his unquiet spirit, dug down to
     the dark depths and dragged it forth, saying, "No longer be at
     peace." Then would come tales of the fiery furnace, what Fire had
     done for Steel, and what Steel had done for Fire. And then the
     Flint might tell of the time when the weather-bound mariners,
     lighting their fires upon the Syrian shore, melted silicious
     stones into gems of glass, and thus led the way to the discovery
     of the transparent pane that gives a crystal inlet to the light
     of our homes; of the mirror in whose face the lady contemplates
     her charms; of the microscope and the telescope by which the
     invisible are brought to sight, and the distant drawn near; of
     the prism by which Newton analysed the rays of light; and of the
     photographic camera in which the sun prints with his own rays the
     pictures of his own adorning. And then both Flint and Steel might
     relate their adventures in the battle-field, whither they had gone
     together; and of fights they had seen in which man struck down his
     fellow-man, and like a fiend had revelled in his brother's blood.
     Thus, even from the cold hearts of flint and steel, man might
     learn a lesson which should make him blush at the "glory of war;"
     and the proud, who despise the teachings of small things, might
     learn to appreciate the truths that are linked to the story of a
     "tinder-box."




CHAPTER XVII.


341. _Since all bodies expand by heat and contract by cold, why does
water, when it reaches the freezing point, expand?_

Because, in freezing, water undergoes crystallization, in which its
particles assume a new arrangement occupying _greater space_.

342. _Why does water never freeze to a great depth?_

Because the covering of ice which is formed upon the surface of the
water prevents the cold air from continuing to draw off the _caloric_
of the water.

[Verse: "For he saith to the snow, Be thou on the earth; likewise to
the small rain, and to the great rain of his strength."--JOB XXXVII.]

343. _Why has this exceptional law of the expansion of water, when
freezing, been ordained?_

Because, but for this, deep waters might be frozen through their whole
depth. This would destroy the myriads of fish and other living things
that inhabit the water. Parts of the earth, now clad in verdure, would
be lost in eternal winter; and even in the most temperate zones it
would take months to effect a thaw; and thawing would be attended with
such floods and subterranean commotion as are terrible to contemplate.

344. _Why are bed-room windows sometimes covered with crystalline forms
on winter mornings?_

Because the vapour of the breaths of the inmates has condensed upon the
window-panes, and formed water. The water has frozen with the cold, and
exhibits the beautiful crystalline forms into which its particles are
arranged.

     Here we have another domestic illustration of the great laws of
     nature. It is the same law which locks the arctic regions in ice
     and decorates our window-panes. This beautiful phenomenon is
     usually witnessed by us on frosty mornings when we rise from our
     beds. It has a story which the observer of nature may read in its
     sparkling eyes. It tells that, although without the air is biting
     cold, God has wrapped a mantle around the face of nature to keep
     it from injury; and that the earth and the waters, though looking
     chilled and dead, have still the warmth of life preserved in their
     bosoms.

345. _What is dew?_

Dew is _watery vapour_ diffused in the air, _condensed_ by coming in
contact with bodies _colder than the atmosphere_.

346. _Why does the air become charged with watery vapour?_

Because, during the day, under the influence of the sun's rays, vapours
are _exhaled_ from all the moist and watery surfaces of the earth.
These vapours are _held in suspension_ in the atmosphere until, by a
change in the temperature of the earth, and of bodies on the surface of
the earth, they are _condensed_, and deposited in translucid drops.

347. _What causes the decline of temperature that favours the
deposition of dew?_

The earth, which during the day _received heat_ from the solar rays,
_radiates the heat_ back into the air, and therefore becomes itself
colder. All the various objects upon the face of the earth also
_radiate heat_ in a greater or lesser degree. And dew will be found to
be deposited upon the surfaces of such bodies in proportion to the fall
of their temperature through _radiation_.

[Verse: "The Lord is my shepherd, I shall not want. He maketh me to
lie down in green pastures."--PSALM XXIII.]

348. _Why is there little or no dew when the nights are cloudy?_

Because clouds act as secondary radiators; and when the _earth_
radiates its heat towards the _clouds_, the clouds again _radiate it
back to the earth_.

[Illustration: Fig. 3.--ILLUSTRATING THE FORMATION OF DEW.]

     If plates of glass be laid over grass-beds, as in the engraving
     Fig. 3, no dew will be deposited on the grass underneath the glass
     plates, although all around the grass will be completely wetted.
     The explanation is that the glasses, being radiators of heat, act
     in the same manner as the clouds, returning the heat to the bodies
     underneath them, and preventing the formation of dew thereon.

349. _Why does dew form most abundantly on cloudless nights?_

Because the heat which is radiated by the earth does not return to it.
The temperature of the earth, and the air immediately upon its surface,
is therefore lowered, and dew is formed.

     It has been observed that sheep that have lain on the grass during
     the formation of dew have their backs completely saturated with
     it, but that underneath the line where their bodies turn to the
     earth, their coats will be dry. In the same manner glass globes
     suspended in the air, on dew forming nights, will be found loaded
     with globules of dew upon the top, but there will be no appearance
     of moisture underneath.

[Verse: "Dost thou know the balancings of the clouds, the wondrous
works of him which is perfect in knowledge."--JOB XXXVII.]

350. _Why are star-lit nights usually colder than cloudy nights?_

Because heat is _radiated_ from the earth, and passes away into the
utmost regions of the atmosphere.

351. _Why is there little dew under branches of thick foliage?_

Because the foliage _acts as a screen_, which prevents the radiated
heat of the earth from passing away.

352. _Why is there no dew formed on windy nights?_

Because, as winds generally consist of dry air, they _absorb and bear
away_ the atmospheric moisture.

353. _Why are valleys and low places chiefly subject to dew?_

Because the elevated lands around them _prevent the disturbance of the
air_ in which the moisture is held.

354. _What bodies are most likely to be covered with dew?_

All bodies that are _good radiators of heat_, such as wool, swansdown,
grass, leaves of plants, wood, &c.

355. _What bodies are likely to receive little dew?_

All _bad radiators of heat_, such as polished metal surfaces, smooth
stones, and polished surfaces generally. Dew will be found to lie more
abundantly upon rough and woolly leaves than upon smooth ones.

356. _At what period of the night is the largest amount of dew usually
formed?_

It is generally supposed that dew is formed _most copiously_ in the
_mornings_ and _evenings_. But _such is not the case_. It is deposited
at all hours of the night, but _most plentifully after midnight_.

357. _Why is dew formed most plentifully after midnight?_

Because, as _radiation_ has been going on for some time, the
temperature of the earth, and of various bodies upon it, has been
_considerably reduced_.

[Verse: "Out of whose womb came the ice? and the hoary frost of
heaven, who hath gendered it?"--JOB XXXVIII.]

358. _In what parts of the world is the maximum of dew formed?_

In warm lands near the sea, or in the vicinity of rivers or lakes,
as the localities of the Red Sea, the Persian Gulf the coast of
Coromandel, in Alexandria, and Chili.

359. _In what parts of the world is the minimum of dew formed?_

It is quite absent in arid regions, in the interior of continents, such
as Central Brazil, the Sahara, and Nubia.

360. _Why is dew seldom formed at sea?_

Because of the defective _radiating_ quality of the surface of _water_.

361. _Why is a heavy dew regarded as the precursor of rain?_

Because a heavy formation of dew indicates that the air is _saturated
with moisture_.

362. _What is hoar-frost?_

Hoar-frost is frozen dew.

363. _Why is hoar-frost said to foretell rain?_

Because it shows that the air is saturated with moisture, and the
temperature of the air being low, the vapours are _likely to condense_,
and produce _showers_.

364. _What is honey-dew?_

Honey-dew is the name applied to a _sweet and sticky moisture_
occasionally deposited upon the leaves of plants. It is, however, an
error to call it _dew_, as it is procured by a class of _insects_
termed _aphides_.

365. _What are fogs?_

Fogs are _clouds_ formed near the earth's surface_;_ but London fogs
are distinguished from clouds by the fact that they embrace in their
vaporous folds the _smoke_ and _volatile matters_ imparted to the air
by the operations of man. This is also the case with fogs generally
that arise near large towns.

[Verse: "Hath the rain a father? or who hath begotten the drops of
dew?"--JOB XXXVIII.]

366. _Why are certain coasts liable to almost perpetual fogs?_

Because of local or geographical agencies which contribute to their
production. The coasts of California are almost constantly wrapped
in fog; and, almost as constantly, the western coast of the American
continent, as far south as Peru. Newfoundland, Nova Scotia, and
Hudson's Bay, are all subject to dense and frequent fogs arising
from the condensation of vapour from the water flowing from the hot
Gulf-stream, coming in contact with the colder air.

367. _What are dry fogs?_

Dry fogs are characterised by a dull opaque appearance of the
atmosphere. They are most common in certain parts of North America,
though they sometimes occur in Germany and in England. They are
generally referred to the _electrical state of the atmosphere_, but the
theory of them is still a matter of doubt.

368. _What is a mist?_

The term _mist_ is generally applied to vapours that rise over _marshy
places_, or the surfaces of _water_, and roll or move over the land.

369. _What is the difference between a mist and a fog?_

Fogs, as they are known to us, generally arise over the _land_, and are
usually mingled with the smoke of large towns. Mists generally arise
over water, or wet surfaces.

370. _Why do mists and fogs disappear at sunrise?_

Because the condensed vapours are again _expanded_ and _dispersed_ by
the heat of the sun's rays.

371. _Why do fogs frequently rise in the morning and fall again in the
evening?_

Because, warmed by the sun's rays, they become more rarefied, and fly
away at an altitude where they _appear_ to be altogether dispelled; but
at night, when the earth _cools by radiation_, the vapours near the
earth _again condense_, and settle in the _form of fog_.

372. _Why do fogs sometimes rest upon a given locality for several days
together, and then disappear?_

They are probably kept near to the surface of the earth by a
superstratum of cold air. A cold air lying _above_, or a cold air lying
_below_, might equally contribute to keep a fog near the surface of a
particular part of the earth, until a _flow of wind_, or a _fall of
rain_, altered the atmospheric condition.

[Verse: "He bindeth up the waters in his thick clouds; and the cloud
is not rent under them."--JOB XXVI.]

     There are many interesting facts connected with the history of
     dew. It has attracted the attention of natural philosophers in all
     ages. But its true theory was never understood until recently.
     The ancients imagined that dews were shed from the stars; and the
     alchemists and physicians of the middle ages believed that the
     dew distilled by night possessed penetrating and wonder-working
     powers. The ladies of those times sought to preserve their beauty
     by washing in dew, which they regarded as a "celestial wash." They
     collected it by placing upon the grass heaps of wool, upon the
     threads of which the magic drops clustered.




CHAPTER XVIII.


373. _What are clouds?_

Clouds are volumes of _vapour_, usually elevated to a considerable
height.

[Illustration: Fig. 4--CIRRO-CUMULUS, OR SONDER CLOUD.]

374. _Whence do clouds arise?_

From the _evaporation of water_ at the earth's surface.

375. _Why do we not see them ascend?_

We do, sometimes, in the form of what we call _mists_, but generally
the vapours that rise and contribute to the formation of clouds are so
thin that they are _invisible_.

[Verse: "With clouds he covereth the light, and commandeth it not to
shine by the cloud that cometh betwixt."--JOB XXXVI.]

376. _Why, if they are invisible when they rise, do they became visible
when they have ascended?_

Because the vapours become _cooled_ in passing through the air, and
form a denser body.

377. _Why, when they are condensed, do they not follow the course of
gravitation, and descend?_

Because the vapours form into _minute vesicles_, which we may call
_vapour bubbles_, and these, being warmed by the sun, are specifically
_lighter than the air_.

Because, also, the lower parts of clouds _do partially_ descend, but
again becoming more _rarefied_ by meeting with a _warmer atmosphere_,
they again ascend, and are thus _poised_ upon the air.

Because, also, there is always a degree of atmospheric motion _upward_,
caused by the _convection of heat_ from the earth's surface. And,
although there must also be downward movements of the air to supply the
place of that which has ascended, still _the heat_ of the ascending
air, _combined with its upward movement_, expands and floats the vapour
of the clouds.

378. _At what height do clouds usually fly?_

They fly at every degree of altitude; but clouds of _specific
character_ are said to fly at given altitudes, or to occupy certain
_ranges of altitude_. We will give their probable altitudes when
speaking of the specific clouds.

[Illustration: Fig. 5.--CIRRUS, OR CURL CLOUD.]

[Verse: "Who giveth rain upon the earth, and sendeth waters upon the
fields."--JOB V.]

379. _How many descriptions of clouds are there?_

There are _seven_.

1. The _Cirrus_ (Fig. 5), estimated range of altitude from 10,000 to
24,000 feet.

2. The _Cumulus_ (Fig. 7), from 3,000 to 10,000 feet.

3. The _Stratus_, an extended continuous level sheet of cloud,
increasing from beneath. They fly very low.

4. The _Nimbus_ (Fig. 10), 1,500 to 5,000 feet.

5. The _Cirro-cumulus_ (Fig. 4), from 3,000 to 20,000 feet.

6. The _Cirro-stratus_ (Fig. 6), from 5,000 to 10,000 feet.

7. The _Cumulo-stratus_ (Fig. 9), from 3,000 to 10,000 feet.

[Illustration: Fig. 6--CIRRO-STRATUS, OR WANE CLOUD.]

     The estimated heights given must be looked upon as very
     conjectural, although they have been derived from the best
     existing authorities. It is sufficient to know that the range of
     the altitude of the various clouds is from that of the _Nimbus_,
     or _thunder cloud_, 1,500 feet, to that of the _Cirrus_, 24,000
     feet, the others being intermediate. The first three of the clouds
     above enumerated constitute what are called the _primary forms_.
     The remaining four are called _secondary forms_, because they
     arise, as their names generally indicate, out of combinations
     of the _primary forms_. Although, from the frequent mingling of
     clouds, it is not always practicable to identify them by the
     adopted classification, still, as there is generally a prevalence
     of one type of cloud over another, the observer would be able
     to distinguish a _"Cirrus sky,"_ or _"Cirro-cumulus sky,"_ &c.
     Upon some occasions the typical characters of the clouds are
     beautifully defined; and the contemplation of their forms, and
     the laws of their formation, affords infinite pleasure to the
     observer. The advantages of scientific knowledge are such, that
     whether you look downwards, to the earth, or upwards to the sky,
     you have still the writing of God to read.

380. _What produces the various shapes of clouds?_

1. The state of the _atmosphere_.

2. The _electrical_ condition of the clouds.

3. The _movements_ of the atmosphere.

4. The _season of the year_.

[Verse: "Behold, he withholdeth the waters, and they dry up; also he
sendeth them out, and they overturn the earth."--JOB XII.]

381. _What are the dimensions of clouds?_

A single cloud has been estimated to have as many as _twenty square
miles of surface_, and to be _above a mile in thickness_, while others
are no larger than a _house_, or a man's _hand_.

[Illustration: Fig. 7.--CUMULUS, OR PILE CLOUD.]

382. _How are clouds affected by winds?_

If _cold winds_ blow upon the clouds, the cold condenses the vapour,
turning the clouds into _rain_. But if _warm dry winds_ blow upon the
clouds, they _rarefy the vapour_ to a greater degree, and temporarily
_disperse the clouds_.

383. _How do winds affect the shapes of clouds?_

When winds are _mild and gentle_, the clouds break into _small
patches_, and rise to a considerable height. But when the winds are
cold and blustering, the clouds fly low, and roll along in _heavy
masses_.

384. _Why are east winds usually dry?_

Because in coming towards England they pass over vast continents of
land, and comparatively little ocean. Hence they are not loaded with
_vapours_.

385. _Why do west winds generally bring rain?_

Because they come across the _Atlantic_, and are heavily charged with
_vapour_.

386. _Why are north winds generally cold and dry?_

Because they come from the arctic ocean, over vast areas of _ice and
snow_.

[Verse: "Terrors are turned upon me: they pursue my soul as the
wind; and my welfare passeth away as a cloud."--JOB XXX.]

387. _Why are south winds warm and rainy?_

Because they come from the southern regions, heated by the _hot earth
and sands_, and as they cross the sea they _absorb a large amount of
vapour_.

[Illustration: Fig. 9.--CUMULO-STRATUS, OR TWAIN CLOUD.]

388. _Why are clouds said to indicate the changes of the weather?_

Because, as it is the _state of the clouds_ that, to a great extent,
determines the _state of the weather_, the formation of the clouds must
predicate approaching changes.

389. _What do cirrus clouds foretell?_

_Cirrus_ clouds foretell _fine_ weather, when they fly high, and are
thin and light.

They foretell _light rain_ when, after a long continuance of fine
weather, they form fleecy lines stretched across the sky.

They foretell a _gale of wind_ when, for some successive days, they
gather in the same quarter of the heavens, as if denoting the point
from which to expect the coming gale. (Fig. 5).

390. _What do cumulus clouds foretell?_

_Cumulus_ clouds, when they are well defined, and advance with the
wind, foretell _fine weather_.

When they are thin and dull, and float against the wind, or in
opposition to the lower currents, they _foretell rain_.

When they increase in size, and become _dull and grey at sunset_, they
predict a _thunder-storm_. (Fig. 7.)

[Verse: "When he made a decree for the rain, and a way for the
lightning and the thunder."--JOB XXVIII.]

391. _What do stratus clouds foretell?_

_Stratus_ clouds foretell _damp and cheerless weather_.

392. _What do nimbus clouds foretell?_

_Nimbus_ clouds foretell _rain_, _storm_, and _thunder_. (Fig. 10.)

393. _What do cirro-cumulus clouds foretell?_

_Cirro-cumulus_ clouds, in summer, foretell _increasing heat_ attended
by _mild rain_, and a _south wind_; but in winter they commonly precede
the _breaking up of a frost_, and the setting in of _foggy and wet
weather_. (Fig. 4.)

394. _What do cirro-stratus clouds foretell?_

_Cirro-stratus_ clouds foretell _rain_ or _snow_, according to the
season of the year.

These clouds extend in long horizontal streaks, thinning away at their
base, and in parts becoming wavy or patchy.

When they are thus defined in the heavens they are a certain indication
of _bad weather_. (Fig. 6.)

395. _What do cumulo-stratus clouds foretell?_

_Cumulo-stratus_ clouds usually foretell a _change of weather_--from
rain to fine, or from fine to rain. (Fig. 9.)

[Illustration: Fig. 10.--NIMBUS, OR STORM CLOUD.]

[Verse: "Behold, I will put a fleece of wool in the floor; and if
the dew be on the fleece only, and it be dry upon all the earth beside,
then shall I know that thou wilt save Israel." * * *]




CHAPTER XIX.


396. _Why are cloudy days colder than sunny days?_

Because the clouds intercept the _solar rays_ in their course towards
the earth.

397. _Why are cloudy nights warmer than cloudless nights?_

Because the clouds _radiate back to the earth_ the heat which the earth
evolves?

Because, also, the clouds radiate to the earth the heat they have
_derived from the solar_ rays during a cloudy day.

398. _Why is the earth warmer than the air during sunshine?_

Because the earth freely _absorbs the heat of the solar rays_; but the
air derives _comparatively little heat_ from the same source.

399. _Why does the earth become colder than the air after sunset?_

Because the earth _parts with its heat freely by radiation_; but the
air does not.

400. _Why do glasses, mats, or screens, prevent the frost from hitting
plants?_

Because they prevent the _radiation of heat from the plants_, and also
from the earth beneath them.

401. _Why are the screens frequently covered with dew on their exposed
sides?_

Because they radiate heat from _both their surfaces_. A piece of glass,
laid horizontally over the earth, would radiate heat both _upwards_ and
_downwards_. But on its lower surface it would _receive_ the radiated
heat of the earth, while from its upper surface it would _throw off its
own heat_ and become cool. Therefore dew would be deposited upon the
_upper_, but not on the _under_ surface.

402. _Why does dew rest upon the upper surfaces of leaves?_

Because the under surfaces receive the _radiated warmth of the earth_.

[Verse: "And it was so: for he rose up early on the morrow, and
thrust the fleece together, and wringed the dew out of the fleece, a
bowl full of water."]

403. _Why are cultivated lands subject to heavier dews than those that
are uncultivated?_

Because cultivation breaks up the hard surface of the earth, and thus
_its radiating power is increased_.

404. _Why is the gravel walk through a lawn comparatively dry while the
grass of the lawn is wet with dew?_

Because gravel is a _bad radiator_, but grass is a _good radiator_.

405. _What benefit results from this arrangement?_

In cultivated lands, where moisture is required, it is _induced_ by
the very necessity which demands it; while in rocky and barren places,
where it would be of no good, dew _does not form_.

406. _Why does little dew form at the base of hedges and walls, and
around the trunks of trees?_

Because those bodies in some degree _counteract the radiation_ of heat
from the earth; and they also _radiate heat_ from their own substances.

407. _Why do heavy morning dews and mists usually come together?_

Because they both have their origin in the _humidity of the
atmosphere_. The temperature of the earth having fallen, dew has been
deposited; but, at the same time, the condensation of the vapour in
the air _has formed a screen over the surface of the earth_, which
has checked _the further radiation of heat_, and, consequently, _the
further formation of dew_. The sun rises, therefore, upon an atmosphere
charged with visible vapour at the earth's surface, and his first
sloping rays, _having little power to warm the atmosphere_, the mist
_continues visible for some time_.

408. _What effect have winds upon the formation of dew?_

Winds, generally, and especially when rapid, prevent the formation of
dew. But those winds that are moist, and _contribute to the formation
of clouds_, indirectly aid the formation of dew _through the formation
of clouds_, and also by the _moisture they impart to the air_.

[Verse: "And Gideon said unto God, * * * Let it now be dry only upon
the fleece, and upon all the ground let there be dew."]

409. _Why does the humidity of the atmosphere sometimes form clouds,
and at others form fogs, mists, dews, &c.?_

The result depends upon the varying _temperature_, _motion_, and
_direction_ of the atmosphere.

A _warm light atmosphere_, of a few day's duration, will elevate the
vapours to the region where they are formed into _clouds_.

A _chill air_, lying upon the surface of the warmer earth, will
occasion _mists_ or _fogs_.

A _cold earth_, acting upon the vapours contained in a _warmer
atmosphere_, will condense them and occasion _dews_.

410. _Why are frosty mornings usually clear?_

Because, in the cold atmosphere which preceded the frost, _there was
but little evaporation_; and now that the frost has set in, the vapours
that existed have become _frozen_ in the form of _hoar-frost_.

411. _Why are clear nights usually cold?_

Because the "screen" afforded by the clouds does not exist; therefore
the heat of the earth escapes, while the vapours of the air are
abstracted from it by condensation into dew, thereby imparting great
_clearness to the nights_.

412. _Why are hoar-frosts, or, as they are termed, "white frosts," so
frequent, and "black frosts" so unusual?_

Because white, or _hoar frosts_, result from the _coldness of the
earth_, which, from its great radiating power, is always varying. But
_black-frosts_ result from the _coldness of the air_, which is liable
to less variation of temperature than the earth.

413. _What is a black-frost?_

A _black-frost_ results from the _coldness of the atmosphere_, which
is at the time overshadowed by a dull cloud, giving a darkness to
everything, and a leaden appearance to the _frozen surface of water_.

414. _Why are black-frosts said to last?_

Because as they result from the temperature of the air, which is less
likely to vary than that of the earth, there is a probability that the
coldness thereof _will last for some time_.

[Verse: "And God did so that night: for it was dry upon the fleece
only, and there was dew on all the ground,"--JUDGES VI.]

415. _What benefits result from the radiation of heat, &c.?_

But for the _radiation of heat_, we should be subjected to the most
unequal temperatures. The setting of the sun would be like _the going
out of a mighty fire_. The earth would become _suddenly cold_, and
its inhabitants would have to bury themselves in warm covering, to
wait the return of day. By the _radiation_ of heat, an _equilibrium of
temperature_ is provided for, without which we should require a new
order of existence.

     The amount of heat which our earth _receives from the sun_, and
     the economy of that heat by the laws of _radiation_, _reflection_,
     _absorption_, and _convection_, are exactly proportionate to the
     necessities of our planet, and the living things that inhabit
     it. It is held by philosophers that any change in the orbit of
     our earth, which would either increase or decrease the amount of
     heat falling upon it, would, of necessity, be followed by the
     _annihilation of all the existing races_. The planets Mercury and
     Venus, which are distant respectively 37 millions of miles, and 63
     millions of miles, from the great source of solar heat, possess
     a temperature which would _melt our solid rocks_; while Uranus
     (1,800 millions of miles), and Neptune (whose distance from the
     sun has not been determined), must receive so small an amount
     of heat, that water, such as ours, would become as solid as the
     hardest rock, and our atmosphere would be resolved into a liquid!
     Yet, poised in the mysterious balance of opposing forces, our orb
     flies unerringly on its course, at the rate of 63,000 miles an
     hour; preserving, in its wonderful flight, that precise relation
     to the sun, which takes from his life-inspiring rays the exact
     degree of heat, which, being shared by every atom of matter, and
     every form of organic existence, _is just the amount needed to
     constitute the heat-life of the world_!




CHAPTER XX.


416. _What is rain?_

Rain is the _vapour of the clouds_ which, being condensed by a fall of
temperature, forms drops of water that descend to the earth.

It is the _return to the earth_ in the form of _water_, of the moisture
_absorbed by the air_ in the form of _vapour_.

417. _Does rain ever occur without clouds?_

It sometimes, but rarely happens, that a sudden transition from
warmth to cold will _precipitate the moisture of the air_, without the
formation of _visible clouds_.

[Verse: "Canst thou lift up thy voice to the clouds, that abundance
of waters may cover thee?"--JOB XXXVIII.]

418. _Why are drops of rain sometimes large and at other times small?_

Because the drops, in falling, _meet and unite_, and also gather
_moisture_ in their descent. The greater the height from which a rain
drop has descended, _the larger it is_, provided that its whole course
lay through a _rainy atmosphere_.

The size of the drops is also influenced by the _amount of moisture
in the atmosphere_, the _degree of cold_, and the _rapidity_ of the
_change of temperature_, by which the drops are produced.

419. _In what seasons of the year are rains most prevalent?_

Throughout _Central Europe_ rains are most prevalent in _summer_, but
in _Southern Europe_ the preponderance is on the side of _winter rains_.

420. _In what months of the year does it rain most frequently in this
country?_

It rains more frequently _from September to March_, than from _March to
September_; but the _heaviest rains_ occur from _March to September_.

421. _Why are there more rainy days from September to March?_

Because the temperature of the air is more frequently lowered to that
degree which _precipitates its vapours_.

     _Months in the order of their comparative wetness_:--1. October.
     2. February. 3. July. 4. September. 5. January. 6. December.

     _Months in the order of their comparative dryness_:--1. March. 2.
     January. 3. May. 4. August. 5. April. 6. November.

422. _In what part of the world does the greatest quantity of rain
fall?_

The greatest _quantity_ of rain falls near the _equator_, and the
amount _decreases towards the poles_.

[Verse: "Who can number the clouds in wisdom? or who can stay the
bottles of heaven."--JOB XXXVIII.]

423. _In what part of the world do the heaviest rains occur?_

The _heaviest_ rains occur in the _tropics_, during the hot season. The
drops of rain in the tropical regions are so large, and the force with
which they descend so great, that their splash upon the skin causes a
_smarting sensation._

424. _In what parts of the world do the least rains occur?_

There are some parts of the earth which are _rainless_, such as Egypt,
the desert of Sahara, the table lands of Persia and Montgolia, the
rocky flat of Arabia Petræ, &c.

425. _How many rainy days are there in a year?_

The frequency of rainy days is greatest in countries near the sea,
and their number decreases the further we journey from the sea-border
towards the inland. In England it rains on an average 152 to 155 days
in the year.

426. _In what part of England does the greatest amount of rain fall?_

In the town of _Keswick_, in Cumberland, where 63 inches of rain fall
in a year; Kendal, in Westmoreland, 58 inches; Liverpool, 34 inches;
Dublin, 25 inches; Lincoln, 24 inches; London, 21 inches.

427. _Why do the heaviest rains occur at the tropics?_

Because the _hot air_ absorbs a large amount of vapour, and rises into
the higher regions of the atmosphere, where the vapours are _suddenly
condensed into heavy rains_, by cold currents from the poles.

428. _Why does the greatest quantity of rain fall at the equator?_

Because the _hot air_ absorbs a large amount of vapour, and as the
atmosphere is usually calm, there is an absence of currents, by which
the saturated air would be removed. In this, which is called "_the
Region of Calms_," rain falls almost daily.

429. _Why are some parts of the earth rainless?_

Because, being situated in tropical or torrid latitudes, and at a
distance from the ocean, the atmosphere above them is always in a _dry
state_.

[Verse: "Thou, O God, didst send a plentiful rain, whereby thou
didst confirm thine inheritance, when it was weary."--PSALM LXVIII.]

430. _When is air said to be saturated with vapour?_

When it cannot take up _a larger quantity_ than that which it already
holds.

     When common salt is dissolved in water, until the water can take
     up no more, the water is then said to be _saturated with salt_.

431. _What proportion of water is air capable of sustaining in the form
of vapour?_

The amount of water held in suspension by the air averages the
following proportion: one thousand _cubic feet of air_ contain as much
vapour as, were it condensed to water, would yield about _two fifths of
a pint_.

But _one thousand cubic feet of air_ are capable of holding
_half-a-pint of water_; and this may be regarded as the _point of
saturation_.

     Thus, in a room ten feet square and ten feet high, the air, _at
     the point of saturation_, would hold in the form of vapour,
     _half-a-pint of water_. It must not be forgotten, however, that
     the point of saturation necessarily varies with the _temperature
     of the air_.

432. _Why are cloudy days and nights not always wet?_

Because the air has not reached the state of _saturation_.

433. _Why does rain purify the air?_

Because it produces motion in the particles of the air, by which they
are _intermixed_. And it precipitates noxious _vapours_, and cleanses
the face of the earth from _unhealthy accumulations_.

434. _Why are mountainous localities more rainy than flat ones?_

Because the mountains _attract the clouds_; and because the clouds
that are flying low are borne against the sides of the mountains and
directed upwards, where they meet with _cold currents of air_.

435. _Why does more rain fall by night than by day?_

Because by night the temperature of the air, heated during the day,
falls to that degree which condenses _its vapours into rain_.

[Verse: "As the hart panteth after the water brooks, so panteth my
soul after thee O God."--PSALM XLII.]

436. _Why do bunches of dried sea-weed indicate the probability of
coming rain?_

Because they readily imbibe moisture, and when they become soft and
damp they show that the air is _approaching the point of saturation_.

437. _Why does the weather-toy, called the "weather-cock," foretell the
probability of rain?_

Because it is made with a piece of cat-gut which swells with moisture,
and as it swells, _shrinks_. The cat-gut is so applied that when it
_shrinks_, it turns a rod which sends the _man_ out of the house, and
when it _dries_ it sends the _woman out_. Therefore, when the _man_
appears, it is a sign of _wet_, and when the _woman_ appears it is a
sign of _dry weather_.

     There is another toy, called the Capuchin, which is made upon the
     same principle. The figure lifts a hood over its head when wet
     is approaching, and takes it off when the weather is becoming
     dry. In this case, a piece of cat-gut is also employed. Various
     weather-toys may be made upon this principle--among others, a
     little umbrella, which will open on the approach of wet, and close
     on the return of fine weather.

     A gentleman once made a wooden horse, which he declared should
     of itself walk across a room, without machinery of any kind. The
     assertion was discredited; but the horse was placed in a room
     close to the wall on one side. The room was locked, and otherwise
     fastened, so that no one could interfere with the experiment.
     After a time the door was opened, and it was found that the horse
     had actually crossed the floor, and stood on the opposite side.
     The horse was made from wood of a peculiar kind, liable to great
     expansion in wet weather, and cut in a manner to produce the
     greatest elongation. The fore hoofs were so made that where they
     were set they would remain, so that the contracting parts should
     draw up from behind. It is easy to understand how, in this way,
     the wooden horse crossed the apartment.

438. _Why does ladies' hair drop out of curl upon the approach of damp
weather?_

Because the hair _absorbs moisture_, which causes its spirals to relax
and unfold.

439. _Why is it said in mountainous countries that rain is coming,
because the mountains are "putting their night-caps on?"_

Because the clouds descend when they are _heavy with vapour_, and being
attracted to the mountain tops they are said to "_cap the mountains."_

[Verse: "Hast thou entered into the treasures of the snow; or hast
thou seen the treasures of the hail."--JOB XXXVIII.]




CHAPTER XXI.


440. _What is snow?_

Snow is _congealed vapour_, which would have formed _rain_; but,
through the coldness of the air, has been _frozen_ in its descent into
_crystalline forms_. (Fig. 1.)

441. _Why is snow white?_

Because it reflects all the component rays of _light_.

442. _Why is snow said to be warm, while white garments are worn for
coolness?_

Snow is _warm_ by virtue of its light and woolly texture. But it is
also warm on account of its _whiteness_; for, had it been _black_, it
would have _absorbed the heat of the sun_, which would have _thawed the
snow_. Instead of which, it _reflects heat_; and the reflected heat
_falls upon_ bodies above the snow, while the _warmth of the earth_ is
preserved _beneath it_. _White clothing is cool_, because it reflects
_from_ the body of the wearer the heat of the sun. _White snow_ is
_warm_, because it _reflects the sun's heat upon bodies_.

     There are few persons but have felt the effect of the sun's rays
     _reflected_ by the white snow on a clear wintry day. And, as
     regards the warmth of snow towards the earth, by preventing the
     radiation of heat, it has been found that a thermometer buried
     four inches deep in snow has shown a temperature of _nine degrees_
     higher than at the surface.

443. _Why are lofty mountains always covered with snow?_

Because the _upper regions_ of the atmosphere are _intensely cold_.

444. _Why are the upper regions of the atmosphere intensely cold?_

Because the _atmosphere_ retains but _little of the heat of the sun's
rays_ as they pass to the earth. Because at high altitudes the air is
_greatly rarefied_. And because the _radiation of heat from the earth_
does not materially affect such _high regions_.

[Verse: "He causeth the vapours to ascend from the ends of the
earth: he maketh lightnings for the rain: he bringeth the wind out of
his treasuries."--PS. XXXV.]

445. _What is meant by the snow line?_

The _snow line_ is the estimated altitude in _all countries_ where
_snow would be formed_. Even at the equator, at an altitude of 15,000
to 16,000 feet from the level of the sea, snow is found upon the
mountain summits, where it perpetually lies. As we proceed north or
south from the equator the _snow line lessens in altitude_. Had we in
England a mountain 6,000 feet high, it would be perpetually _crowned
with snow_.

446. _Why do we hear of red snow?_

Red snow is the name given to the snow in the arctic regions upon which
a minute vegetable (probably the _Protoccus nivalis_) grows, imparting
to the snow a red colour. Recent microscopic investigations have
shown it to consist of a minute vegetable cell, which secretes a red
colouring matter.

     Snow is found to be of greater importance to man than is generally
     supposed. But, although in this country we are enabled to
     recognise the hand of Providence in the gift, there are latitudes
     wherein the blessing thus conferred is more deeply felt. In such
     countries as Canada, Sweden, and Russia, the falling of snow
     is looked for with glad anticipations, quite equalling those
     which herald the "harvest-home" of England, or the "vintage" of
     France. No sooner is the ground covered with snow, than cranky
     old vehicles that had been jolting over rough roads, and sticking
     fast in deep ruts of mud, are wheeled aside, and swift sledges
     take their place. Towns distant from each other find an easy mode
     of communication; the markets are enlivened, and trade thrives.
     Snow supplies a kind of railroad, covering the entire face of the
     country, and sledges glide over it, almost with the speed of the
     locomotive.

447. _What is sleet?_

_Sleet_ is snow which, in falling, has met with a _warmer current of
air_ than that in which it congealed. It therefore partially melts and
forms a kind of _wet snow_.

448. _What is hail?_

_Hail_ is also the _frozen moisture of the clouds_. It is probably
formed by _rain drops_ in their descent to the earth, meeting with an
_exceedingly cold current of air_ by which they become _suddenly frozen
into hard masses_.

It is also supposed that the _electrical_ state of the air and of the
clouds influences the formation of _hail_.

[Verse: "If the clouds be full of rain, they shall empty themselves
upon the earth."--ECCLES. XI.]

449. _Why is it supposed that the electrical state of the air and the
clouds affects the formation of hail?_

Because hail is more common in the _summer_ than at other seasons, and
is frequently attended by storms of _thunder and lightning_.

450. _Why do hail-storms most frequently occur by day?_

Because the clouds, being charged with vapour to saturation, favour the
formation of hail by _sudden_ electrical or atmospheric changes. In the
gradual cooling of night, the clouds would expend themselves in rain.

     Astonishing facts respecting hail-storms are upon record. In 1719
     there fell at Kremo, hailstones weighing six pounds. In 1828 there
     was a fall of ice at Horsley, in Staffordshire, some of the pieces
     of which were three inches long, by one inch broad; and other
     solid pieces were about three inches in circumference. Hail storms
     are most frequent in June and July, and least frequent in April
     and October. Hail clouds float much lower in the sky than other
     clouds; their edges are marked by frequent heavy folds; and their
     lower edges are streaked with white, the other portions being
     massive and black. (Fig. 10.)




CHAPTER XXII.


451. _What is light?_

Light, according to Newton, is the effect of luminous particles which
dart from the surfaces of bodies in all directions. According to this
theory, the solar light which we receive would _depart from the sun and
travel to the earth_.

According to Huyghens, light is caused by an _infinitely elastic ether,
diffused through all space_. This ether, existing everywhere, is
_excited into waves, or vibrations, by the luminous body_.

     The theory of light is so undetermined that neither the views
     of Newton, nor those of Huyghens, can be said to be exclusively
     adopted. Writers upon natural philosophy seize hold of either or
     both of those theories, as they present themselves more or less
     favourably in the explanation of natural phenomena. In "_The
     Reason Why,"_ as we have to speak of the _effects_ of light rather
     than of its _cause_, we shall avoid, as far as possible, the
     doubtful points. But let no one be discouraged by the fact that
     the theory of light, as, indeed, of all the imponderable agents,
     is imperfectly understood. Rather let us rejoice that there are
     vast fields of discovery yet to be explored; and that light, the
     most glorious and inspiring element in nature, invites us from the
     sun, the moon, and the stars, and from the face of every green
     leaf and variegated flower, to search out the wonders of its
     nature, and further to exemplify the goodness and wisdom of God.

[Verse: "And God said, Let there be light: and there was light."]

452. _What is the distance of the sun from the earth?_

Ninety five millions of miles.

453. _At what rate of velocity does light travel?_

At the rate of 192,000 miles in a _second_, through our _atmosphere_;
and 192,500 miles in a _second_ through a _vacuum_.

454. _How long does light take to travel from the sun to the earth?_

Eight minutes and thirteen seconds.

455. _What is the constitution of the sun?_

It is a spherical body, 1,384,472 times larger than the earth.

456. _From what does the luminosity of the sun arise?_

From a luminous atmosphere, or, as M. Arago named it, _photosphere_,
which completely surrounds the body of the sun, and which is probably
_burning with great intensity_.

457. _What are the minor sources of light?_

Light may be produced by _chemical action_, by _electricity_, and by
_phosphoresence_, in the latter of which various agencies unite.

458. _What is a ray of light?_

A _ray_ of light is the _smallest portion_ of light which we can
recognise.

459. _What is a medium?_

A _medium_ is a body which affords _a passage for the rays_ of light.

460. _What is a beam of light?_

A _beam_ of light is a _group of parallel rays_.

461. _What is a pencil of light?_

A _pencil_ of light is a body of rays which _come from or move towards
a point_.

[Verse: "And God saw the light, that it was good: and God divided
the light from the darkness."--GEN. I.]

462. _What is the radiant point?_

The _radiant point_ is that _from which diverging rays of light are
emitted_.

463. _What is the focus?_

The _focus_ is the point to which _converging rays are directed_.

     _Diverging_, starting from a point, and separating. _Converging_,
     drawing together towards a point.

464. _What is the constitution of a ray of light?_

A ray of _white light_, as we receive it from the sun, is composed of
_a number of elementary rays_, which, with the aid of a triangular
piece of glass, called a _prism_, may be separated, and will produce
under refraction the following colours:--

1. An _extreme red_ ray--a mixture of _red_ and _blue_, the red
_predominating_.

2. _Red._

3. _Orange_--red passing into and combining with yellow.

4. _Yellow_--the most luminous of all the rays.

5. _Green_--yellow passing into and combining with the blue.

6. _Blue._

7. _Indigo_--a dark and intense blue.

8. _Violet_--blue mingled with red.

9. _Lavender grey_--a neutral tint.

10. Rays called _fluorescent_, which are either of a _pure silvery
blue_, or a _delicate green_.

465. _Why is a ray of light, which contains these elementary rays,
white?_

Because the colour of light is governed by the _rapidity of the
vibrations of the ether-waves_. When a ray of light is refracted by, or
transmitted through a body, its _vibrations are frequently disturbed
and altered_, and thus a _different impression_ is made upon the _eye_.

Light which gives 37,640 vibrations in _an inch_, or
458,000,000,000,000 in a _second of time_, produces that sensation
upon the eye which makes the object that directs the vibrations appear
_red_. _Yellow_ light requires 44,000 vibrations _in an inch_, and
535,000,000,000,000 in a _second of time_. And the other colours
enumerated (_see_ 464) all require different _velocities of vibration_
to produce the colours by which they are distinguished.

[Verse: "The light of the body is the eye: if therefore thine eye be
single, thy whole body shall be full of light."--MATT. V.]

     Accepting the theory of vibrations, and applying it to the
     elucidation of the phenomena of light--it is unnecessary, we
     think, to believe that a ray of _white_ light _contains_ rays
     in _a state of colour_. It is said that if we divide a circular
     surface into parts, and paint the various colours in the order
     and proportions in which they occur in the refracted ray, and
     then spin the circle with great velocity, the colours will blend
     and appear _white_. But such is not the case; the result is in
     some degree an illusion, arising out of the sudden removal of the
     impression made upon the eye by the colours; and if a piece of
     white paper be held by the side of the coloured circle in motion,
     the latter will be found to be _grey_. When it is remembered
     that in colouring a white surface with thin colours, the white
     materially qualifies the colours, it must be admitted that the
     experiment fails to support the assertion that the colours of
     the spectrum produce white. But there can be no difficulty in
     understanding that a ray of light undergoing _refraction_, becomes
     divided into minor rays, which _differing in their degrees of
     refrangibility_, vary also in the _velocity of their vibrations_,
     and produce the several sensations of colour.

466. _Why is a substance white?_

Because it reflects the light that falls upon it _without altering its
vibrations._

467. _Why is a substance black?_

Because it _absorbs the light_ and _puts an end to the vibrations_.

468. _Why is the rose red?_

Because it imparts to the light that falls upon it that _change in its
vibratory condition_, which produces on our eyes the _sensation of
redness_.

469. _Why is the lily white?_

Because it reflects the light without altering its vibrations.

470. _Why is the primrose yellow?_

Because, though it receives white light, it alters its vibrations to
44,000 in an inch, and 535,000,000,000,000 in a second, and this is
the velocity of vibration which produces upon the eye a _sensation_ of
_yellow_.

[Verse: "But if thine eye be evil, thy whole body shall be full of
darkness. If therefore the light that is in thee be darkness, how great
is that darkness."--MATT. V.]

471. _Why are there so many varieties of colour and tint in the various
objects in nature?_

Because every surface has a peculiar constitution, or atomic condition,
_by which the light falling upon it is influenced_. In tropical
climates, where the brightness of the sun is the most intense, there
the colours of natural objects are the richest; the foliage is of the
darkest green; the flowers and fruits present the brightest hues; and
the plumage of the birds is of the most gaudy description. In the
temperate climates these features are more subdued, still bearing
relation to the degree of light. And at a certain depth of the ocean,
where light penetrates only in a slight degree, the objects that abound
are nearly colourless.

     It has been held by many philosophers (and the theory is so far
     conclusive that it cannot be dispensed with) that there is an
     analogy between the vibratory causes of _sound_, and the vibratory
     causes of _colour_. Any one who has seen an Æolian harp, and
     listened to the wild notes of its music, will be aware that the
     wires of the harp are swept by accidental currents of air; that
     when those currents have been strong, the notes of the harp
     have been raised to the highest pitch, and as the intensity of
     the currents has fallen, the musical sounds have deepened and
     softened, until, with melodious sighing, they have died away. No
     finger has touched the strings; no musical genius has presided
     at the harp to wake its inspiring sounds; but the vibration
     imparted to the air, as it swept the wires, has alone produced the
     chromatic sounds that have charmed the listener. If, then, the
     varied vibrations of the _air_ are capable of imparting dissimilar
     sensations of _sounds_ to the _ear_, is it not only possible, but
     probable, that the different vibrations of _light_ may impart the
     various sensations of _colours_ to the _eye_?




CHAPTER XXIII.


472. _What is the refraction of light?_

When rays of light fall _obliquely_ upon the surface of any
_transparent medium_, they are slightly diverted from their course.
This alteration of the course of the rays is called _refraction_, and
the degree of refraction is influenced by the difference between the
_densities_ of the mediums _through which light is transmitted_.

[Verse: "Let your light so shine before men, that they may see your
good works, and glorify your father which is in heaven."--MATT. V.]

473. _If a ray of light falls in a straight line upon a transparent
surface, is it then refracted?_

In that case the ray pursues its course--_there is no refraction_.

474. _Is the direction in which the rays are bent, or refracted,
influenced by the relative densities of the media?_

A ray of light falling slantingly upon a _window_, in passing through
it is slightly brought to the _perpendicular_; and if it then falls
upon the surface of water, it is still further brought to the
perpendicular in _passing through the water_.

475. _Is light refracted in passing from a dense medium to a thinner
one?_

It is; but the _direction of the refraction_ is just the opposite to
the instance just given; a ray of light passing through _water_ into
_air_, does not take a more _perpendicular course_, but becomes more
_oblique_.

[Illustration: Fig. 11.]

476. _Why, if a rod or a spoon be set in an empty basin, will it appear
straight, or of its usual shape?_

Because the rays of light that are reflected from it all pass through
the same medium, the _air_.

477. _Why if water be poured into the basin will the rod or spoon
appear bent?_

Because the rays of light that pass through the _water_ are _reflected
in a different degree_ to those that pass through the air.

[Verse: "Evening, and morning, and at noon, will I pray, and cry
aloud; and he shall hear my voice."--PSALM LV.]

     Place in the bottom of an empty basin (Fig. 11.) a shilling;
     then stand in such a position at the point B that the line of
     sight, over the edge of the basin, just excludes the shilling
     from view. Then request some one to pour water into the basin,
     until it is filled to C (Fig. 12.), keeping your eye fixed upon
     the spot. The shilling will gradually appear, and will soon come
     entirely in view. Not only will the shilling be brought in view,
     but also portions of the basin before concealed. This is owing to
     the rays of light passing from the bottom through the water in a
     direction _more perpendicular_ than they would have done through
     the air; but on leaving the water they become more _oblique_, and
     hence they convey the image of the shilling _over the edge of the
     basin_, which otherwise would have obstructed the view.

[Illustration: Fig. 12.]

478. _Why is it that in cloudy and showery days we see the sun's rays
bursting through the clouds in different directions?_

Because, in passing through clouds of _different densities_ the rays
are _bent out of their course_.

479. _Why is the apparent depth of water always deceptive?_

Because the light reflected from the objects at the bottom is
_refracted_ as it leaves the water.

480. _How much deeper is water than it appears to be?_

About _one-third_. A person bathing, and being unable to swim, should
calculate before jumping into the water, that if it _looks two feet
deep_, it is quite _three feet_.

481. _Why can we seldom at the first attempt touch anything lying at
the bottom of the water with a stick?_

Because we do not allow for the _different refractive powers_ of water
and of air.

[Verse: "I do set my bow in the cloud, and it shall be for a token
of a covenant between me and the earth."]

482. _Why do we see the sun before sunrise, and after sunset?_

Because of the refractive effects of the atmosphere. Rays of light,
passing obliquely from the sun through the air to the earth, are
refracted three or four times by the varying density of the medium.
Each refraction bends the rays towards the _perpendicular_; and hence
we see the sun _before it rises_ and _after it sets_.

[Illustration: Fig. 13.--DIAGRAM EXHIBITING THE REFRACTION OF THE SUN'S
RAYS IN PASSING THROUGH THE ATMOSPHERE.]

483. _Why do figures, viewed through the hot air proceeding from
furnaces, and from lime-kilns, appear distorted and tremulous?_

Because the ever varying density of the air which is flying away in hot
currents, and succeeded by cold, _constantly changes the refractive
power_ of the medium through which the figures are viewed.

484. _Why do the stars twinkle?_

Because their light reaches us through _variously heated and moving
currents of air_. In this case the earth is the _kiln_, and the _stars_
the _object_ that is _viewed through the refractive medium_.

485. _Why does much twinkling of the stars foretell bad weather?_

Because it denotes that there are _various ærial currents_ of different
temperatures and densities, producing _atmospheric disturbance_.

[Verse: "And it shall come to pass, when I bring a cloud over the
earth, that the bow shall be seen in the cloud."--GENESIS IX.]

486. _What causes the rainbow?_

The _refraction_ of the sun's rays by the _falling rain_.

487. _Why does the rainbow exhibit various colours?_

The colours belong to the _elementary rays of light_; and these rays
having _different degrees of refrangibility_, some of them are bent
more than others; they are therefore separated into _distinct rays of
different colours_.

488. _Why are there sometimes two rainbows?_

Because the rays of _refracted_ light, reflected upon other drops of
rain, are _again_ refracted, and then _reflected again_, forming a
secondary bow.

489. _Why are the colours of the secondary bow arrayed in the reverse
order of the primary bow?_

Because the secondary bow is _a reflection_ of the primary bow, and,
like all reflections, is reversed.

490. _Why are reflections reversed?_

Because those rays which _first reach_ the reflecting surface are the
_first returned_. If you hold your open hand towards the looking-glass,
the light passing from the point of your finger will reach the
reflector and be returned before the rays that pass from the back parts
of the hand. Hence the image of the hand will present the reflection of
the finger point towards the point of the finger.

491. _Why are the colours of the secondary rainbow fainter than those
of the primary?_

Because they are derived from the _refraction and reflection_ of rays
which have _already_ been refracted and reflected, and thereby _their
intensity has been diminished_.

492. _What is a lunar rainbow?_

A _lunar rainbow_ is caused by the light of the _moon_, in the same
manner as the _solar rainbow_ is caused by the light of the _sun_.

[Verse: "I am come a light into the world, that whosoever believeth
in me should not abide in darkness."--JOHN XIII.]

493. _Why is the lunar rainbow fainter than a solar rainbow?_

Because the _light of the moon_ is the _reflected light of the sun_,
and is therefore _less intense_.

494. _What is a halo?_

A halo is a _luminous ring_, which forms between the eye of the
observer and a luminous body.

Haloes may appear around the disc of the sun, moon, or stars. But in
this country the _lunar_ haloes are the most remarkable and frequent.

495. _What is the cause of the luminous ring?_

The _refraction of light_ as it passes through an intervening _cloud_,
or a stratum of _moist_ and _cold air_.

496. _Why are haloes sometimes large and at other times small?_

Because they are sometimes formed _very high_ in the atmosphere, at
other times _very low_. Being high, and farther removed from the
spectator, and nearer the source of light, they appear _smaller_; while
the nearer they are, the _larger they appear_.

497. _Why do haloes foretell wet weather?_

Because they show that there is a great amount of atmospheric moisture,
which will probably form _rain_.

498. _Why do glass lustres and chandeliers exhibit "rainbow colours"?_

Because they _refract the rays of light_ in the same manner as the rain
drops.

499. _Why does a soap bubble show the prismatic colours?_

Because, like a large rain drop, it _refracts the rays of light_, and
shows the elementary rays.

500. _What causes the rich tints displayed by "mother-of-pearl?"_

The _refraction of the light_ that falls upon the surface of the pearl.

[Verse: "Light is sown for the righteous, and gladness for the
upright in heart."--PSALM XCVII.]

501. _What causes the brilliant colours of the diamond?_

The _refraction_ of the rays of light by the various _facets_ of the
diamond.

     The refraction of light, and the production of prismatic colours,
     surrounds us with most interesting phenomena. The laundress,
     whose active labours raise over the wash-tub a soapy froth,
     performs inadvertently one of the most delicate operations of
     chemistry--the chemistry of the imponderable agents--and the
     result of her manipulations manifests itself in the delicate
     colours that dance like a fairy light over the glassy films that
     follow the motion of her arms. The laughing child, throwing a
     bubble from the bowl of a tobacco pipe into the air, performs
     the same experiment, and produces a result such as that which
     filled the philosophic Newton with unbounded joy. The foam of the
     seashore, the plumage of birds, the various films that float upon
     the surface of waters, the delicate tints of flowers, and the rich
     hues of luscious fruits, all combine to remind us, that every ray
     of light comes like an angelic artist sent from heaven, bearing
     upon his palette the most celestial tints, with which to beautify
     the earth, and show the illimitable glory of God.




CHAPTER XXIV.


502. _What is the difference between the refraction and the reflection
of light?_

_Refraction_ is the deviation of rays of light from their course
through the interference of a _different_ medium; _reflection_ is
the return of rays of light which, having fallen upon a surface, are
repelled by it.

503. _What is the radiation of light?_

The _radiation_ of light is its _emission in rays_ from the surface of
a _luminous body_.

504. _Do all bodies radiate light?_

All bodies radiate light; but those that are not in themselves primary
sources of light, are said to _reflect it_.

505. _Do black bodies reflect any light?_

Black bodies _absorb_ the light that falls upon them. But they reflect
a _very small_ degree of light.

506. _Why is glass transparent?_

Because its atoms are so arranged that they allow the vibrations of
light to continue through their substance.

[Verse: "As in water face answereth to face, so the heart of man to
man."--Proverbs xxvii.]

507. _Does glass obstruct the passage of any portion of light?_

Glass _reflects_ (sends back) a very small portion of light. This may
be observed by holding a piece of paper, or a hand, a few inches from
a window, when a faint reflection of it will be visible. Probably the
small amount of light _reflected by transparent glass, which gives a
passage to the greater part of the rays_, may serve to illustrate the
small amount of light reflected from _black surfaces_, which _absorbs
the greater portion of light_.

     Instead of a piece of white paper, hold a piece of _black cloth_
     two or three inches from the window-pane, and you will have two
     reflections so weak that the image of the cloth will be almost
     lost. The first reflection is that of the very small amount of
     light from the black surface on to the glass, and the second
     reflection is that of the inconceivably small amount returned by
     the glass, and by which the faint image of the black cloth is
     produced. But put the black cloth outside of the window-pane, and
     then hold an object before them, and you will find that the _two
     weak reflectors, acting together_, produce an improved image, or
     reflection.

508. _Why, if a book is held between a candle-light and the wall, does
a shadow fall upon the wall?_

Because the rays of light are _intercepted_ by the book.

509. _Why do the rays pass over the edges of the book in a direct line
with the flame of the candle?_

Because light always travels in _straight lines_.

510. _Why is there some amount of light even where shadows fall?_

Because, _as all objects reflect light_, some of them throw their light
into the field of the shadow.

511. _Why are some substances opaque to light?_

Because the arrangement of their particles will not admit of the
_vibrations of the luminous ether_ passing through them.

     Opaque--impervious to rays of light.

512. _Why do we see our faces reflected in mirrors?_

Because the rays of light from our faces are _reflected_ by the surface
of the _quicksilver_ at the back of the glass.

[Verse: "The day is thine, the night also is thine: thou hast
prepared the light and the sun."--PSALM LXXIV.]

513. _Why does the quicksilver reflect the rays of light?_

Because, being _densely opaque to light_, and presenting also a bright
surface, it is a good reflector, and it _throws back the whole of the
rays_.

514. _What has the glass to do with the reflection?_

The glass has _nothing to do with the reflection_, except that it
affords a field upon which the reflecting surface of the quicksilver is
spread; and it keeps the air and dirt from _dulling the quicksilver_.

     The parts of a mirror from which the quicksilver is rubbed away
     give no reflection that could assist the reflecting power of the
     quicksilver. That the surface of the glass does not reflect the
     image, is shown by the fact, that if you put the point of any
     object against the glass, the thickness between the point and the
     place where the reflection of it begins, will _show the exact
     thickness of the glass_.

515. _Why does a compound mirror (a multiplying mirror) exhibit a large
number of images of one object._

Because all objects reflect rays of light in _every direction_, and
therefore the different mirrors, being at _various angles_, receive
_each a reflection_ of the same object.

516. _Why does a window-pane appear to be a better reflector by
candle-light than by day-light?_

The reflecting power of glass is precisely the same by night as by
day, and is always very feeble. But it appears to be greater by night,
_because the surrounding darkness increases the apparent strength of
the reflection_.

517. _How do we know that objects reflect light in every direction?_

Because if we _prick a hole in a card with a pin_, and then look
through that small hole upon a _landscape_, we can see some miles of
country, and some thousands of objects; every part of every object
throughout the whole scene, must have sent rays of light the small hole
pricked in the card.

[Verse: "Such knowledge is too wonderful for me; it is high, I
cannot attain unto it."--PSALM CXXXIX.]

     At one extremity of the landscape, viewed through the hole in the
     card, there may be a forest of trees; in the distance there may be
     hills bathed in golden light, and overhung with glittering clouds;
     in the mid-distance there may be a river winding its course along,
     as though it loved the earth through which it ran, and wished,
     by wandering to and fro, to refresh the thirsty soil; in the
     foreground may be a church, covered by a million ivy leaves; and
     grouping towards the sacred edifice may be hundreds of intending
     worshippers, old and young, rich and poor; flowers may adorn the
     path-ways, and butterflies spangle the air with their beauties;
     yet every one of those objects--the forest, the hills, the clouds,
     the river, the church, the ivy, the people, the flowers, the
     butterflies--must have sent rays of light, which found their way
     through the little hole in the card, and entered to paint the
     picture upon the curtain of the eye.

     This is one of the most striking instances that can be afforded
     of the wonderful properties of light, and of the infinitude of
     those luminous rays that attend the majestic rising of the sun.
     Not only does light fly from the grand "ruler of the day" with
     a velocity which is a million and a half times greater than
     the speed of a cannon-ball, but it darts from every reflecting
     surface with a like velocity, and reaches the tender structure of
     the eye so gently that, as it falls upon the little curtain of
     nerves which is there spread to receive it, it imparts the most
     pleasing sensations, and tells its story of the outer world with a
     minuteness of detail, and a holiness of truth. Philosophers once
     sought to _weigh_ the _sunbeam_; they constructed a most delicate
     balance, and suddenly let in upon it a beam of light; the lever
     of the balance was so delicately hung that the fluttering of a
     fly would have disturbed it. Everything prepared, the grave men
     took their places, and with keen eyes watched the result. The
     sunbeam that was to decide the experiment had left the sun eight
     minutes prior to pass the ordeal. It had flown through ninety-five
     millions of miles of space in that short measure of time, and it
     shot upon the balance with unabated velocity: but the lever moved
     not, and the philosophers were mute.




CHAPTER XXV.


518. _Why, when we move before a mirror, does the image draw near
to the reflecting surface as we draw near to it, and retire when we
retire?_

Because the lines and angles of _reflection_ are always equal to the
lines and angles of _incidence_.

519. _What is the line of incidence?_

If a person stands in a direct line before a mirror, the line through
which the light travels from him to the mirror is _the line of
incidence_.

     _Incidence_--falling on.

[Verse: "Blessed be the Lord, who daily loadeth us with benefits,
even the God of our salvation."--PSALM LXVIII.]

520. _What is the line of reflection?_

The _line of reflection_ is the line in which the rays of light are
returned from the image formed in the glass to the eye of the observer.

     _Reflection_--a turning back.

521. _What is the angle of incidence?_

The _angle_ of incidence is the angle which rays of light, falling on a
reflecting surface, make with a line perpendicular to that surface.

[Illustration: Fig. 14.--EXPLAINING THE LINES AND ANGLES OF INCIDENCE
AND OF REFLECTION.]

522. _What is the angle of reflection?_

The _angle_ of reflection is the angle which is formed by the returning
rays of light, and a line perpendicular to the reflecting surface. It
is always _equivalent_ to the angle of incidence.

     Take a marble and roll it across the floor, so that it shall
     strike the wainscot obliquely. Let A in the diagram represent the
     point from which the marble is sent. The marble will not return to
     the hand, nor will it travel to the line B, but will bound off, or
     be _reflected_, to C. Now B is an imaginary line, _perpendicular
     to the reflecting surface_; and it will be found that the path
     described by the marble in _rolling to the surface and rebounding
     from it_, form, with the line B, two angles that are _equal_.
     These represent the angles of _incidence_ and of _reflection_,
     and explain why the reflection of a person standing at A before a
     mirror, would be seen by another person standing at C. This simple
     law in optics explains a great many interesting phenomena, and
     therefore it should be clearly impressed upon the memory.

[Verse: "And God made two great lights; the greater light to rule
the day, and the lesser light to rule the night: he made the stars
also."--GEN. I.]

523. _Why do windows reflect the sun in the evening?_

Because the eye of the observer is in the _line of the reflection_.

524. _Why do windows not reflect the sun at noon?_

They do, but our eyes are not then in the _line of the reflection_.

[Illustration: Fig. 15.--SHOWING THE LINES OF INCIDENCE AND REFLECTION
OF THE SUN'S RAYS AT NOON AND AT EVENING.]

     It is obvious from the foregoing diagram that the evening rays of
     reflection fall upon the eyes of spectators, while the reflections
     at noon are so perpendicular that they are lost.

525. _Why do the sun and moon appear smaller when near the meridian,
than when near the horizon?_

Because, when near the horizon, they are brought into _comparison with
the sizes of terrestrial objects_; but when near the meridian they
occupy the centre of a vast field of sky, and as there are no objects
of comparison surrounding them, they _appear smaller_.

[Verse: "There is no darkness nor shadow of death, where the workers
of iniquity may hide themselves."--JOB XXXIV.]

     This is one "Reason Why," assigned by some observers. But there is
     also another reason to be found in the fact that, when the sun or
     moon is near the horizon, we view it through a _greater depth of
     atmosphere_ than we do when at the meridian. (_See_ Fig. 13.) A
     straight line passed upward through the air, would not be so long
     as that which passes to S. Consequently, as the air is generally
     impregnated with moisture, at the time when these effects are
     observed, the rays of light are caused to diverge more, and the
     disc of the sun or moon _appears magnified_. Probably both of
     these reasons contribute to the effect. This latter reason also
     explains why the disc of the sun or moon may sometimes appear
     _oval_ in shape, the lower stratum of air being more loaded with
     moisture than that through which we view the upper part of the
     disc.

526. _Why do our shadows lengthen as the sun goes down?_

Because light travels only in _straight lines_, and as the sun
descends, the direction of his rays becomes more _oblique_, thereby
causing longer shadows.

527. _What is the cause of the optical illusions frequently observed in
nature?_

There are various kinds of natural optical illusions:--

The _mirage_, in which landscapes are seen reflected in burning sands.

The _fata morgana_, in which two or three reflections of objects occur
at the same time.

The _ærial spectra_, or ærial reflections, &c.

[Illustration: Fig. 16.--ILLUSTRATING THE APPEARANCE OF PHANTOM SHIPS.]

The optical illusions above enumerated owe their origin to various
atmospheric conditions, in which _refractions_ and _reflections_
are _multiplied_ by the different densities of atmospheric layers.
They chiefly occur in hot countries, where, from the varying effects
of heat, the conditions of atmospheric refraction and reflection
frequently prevail in their highest degree.

[Verse: "In the morning ye say, it will be foul weather to-day, for
the sky is red and lowering."--MATT. XVI.]

528. _Why do we have twilight mornings and evenings?_

Because the coming and the departing rays of the sun are _refracted_
and _reflected_ by the upper portions of the atmosphere. (_See_ Fig.
13.)

529. _How long before the sun appears above the horizon does the
reflection of his light reach us?_

The time _varies_ with the refracting and reflecting power of the
atmosphere, from _twenty minutes_ to _sixty minutes_. But the sun's
position is usually _eighteen degrees_ below the horizon when twilight
begins or ends.

530. _Why is the sky blue?_

The white light of the sun falls upon the earth without change; it
is then reflected back by the earth, and as it passes through the
atmosphere portions of it are again returned to us, and this double
reflection produces a _polarised_ condition of light which imparts to
vision the sensation of a _delicate blue_. (_See_ 549.)

531. _Why do the clouds appear white?_

Because they reflect back to us the solar beam _unchanged_.

532. _Why does the sky appear red at sunset?_

Because the light vapours of the air, which are condensed as the sun
sets, refract the rays of light, and produce red rays. The refraction
which produces _red_ requires only a _moderate degree of density_.

533. _Why do the clouds sometimes appear yellow?_

Because there is a larger amount of vapour in the air, which produces a
different degree of refraction, _resulting in yellow_.

534. _Why does a yellow sunset foretell wet weather?_

Because it shows that the air is heavy with vapours. The refraction
that produces _yellow_ requires a greater degree of density.

[Verse: "When it is evening ye say it will be fair weather, for the
sky is red."--MATT. XVI.]

535. _Why does a red sunset foretell fine weather?_

Because the redness shows that the vapours in the air _towards the
West_, or wet quarter, are _light_, as is evidenced by the degree of
refraction of the sun's rays.

536. _Why does a red sunrise foretell wet?_

Because it shows that _towards the East_, or dry quarter, the air is
charged with vapour, and therefore probably at other points the air has
reached _saturation_.

537. _Why does a grey sunrise foretell a dry day?_

Because it shows that the vapours in the air are _not_ very dense.

538. _Why is "a rainbow in the morning the shepherd's warning?"_

Because it shows that _in the West_, or wet quarter, the air is
_saturated_ to the rain point.

539. _Why is "a rainbow at night the shepherd's delight?"_

Because it shows that the _rain is falling in the East_, and as that
is a dry quarter, it will _soon be over_. Rainbows are always seen in
opposition to the sun.




CHAPTER XXVI.


540. _What is the difference between light and heat?_

The most obvious distinction is, that light acts upon _vision_, and
heat upon _sensation_, or feeling.

Another distinction is, that _heat expands all bodies_, and alters
their atomic condition; while _light_, though usually attended by heat,
does not display the same expansive force, but produces various effects
which are _peculiar to itself_.

[Verse: "Ye are the light of the world. A city that is set on a hill
cannot be hid."--MATTHEW V.]

541. _Are light and heat combined in the solar ray?_

Yes. A ray of light, as well as containing elementary rays that produce
colours under refraction, contains also _chemical rays_, and _heat
rays_.

542. _How do we know that light and heat are separate elements?_

Because we have _heat rays_, as from dark hot iron, from various
chemical actions, and from friction, which are _unattended by the
development of light_. And we have light, or luminosity, such as that
of _phosophoresence_, which is unaccompanied by any appreciable degree
of heat.

But, besides this confirmation, further proof is afforded by the fact,
that in passing rays of solar light through media that are _transparent
to heat_, but not to _light_, the heat rays may be _separated_ from the
luminous rays, and _vice versa_.

     Black glass, and black mica, which are nearly _opaque to light_,
     are _transparent to heat_ to the extent of ninety degrees out of
     a hundred. While pale green glass, coloured by oxide of copper,
     and covered with a coating of water, or a thin coating of alum,
     will be perfectly _transparent to light_, but will be almost
     quite _opaque to heat_. These remarks apply, in a greater or less
     degree, to various other substances.

543. _In what respects are light and heat similar?_

Both heat and light have been referred to minute vibratory motions
which occur, under exciting causes, in a very subtile elastic medium.

They are both united in the sun's rays.

They are both subject to laws of absorption, radiation, reflection, and
refraction.

They are both essential to life, whether animal or vegetable.

Both may be developed in their greatest intensity by electricity.

They are both imponderable.

[Verse: "When I consider thy heavens, the work of thy fingers, the
moon and the stars which thou hast ordained:"]

544. _In what respects are light and heat dissimilar?_

Heat frequently exists without light.

Light is usually attended with heat.

Light may be instantly extinguished, but Heat can only be more
gradually reduced, by diffusion.

The solar rays deliver heat to the earth by day, and the heat remains
with the earth when the light has departed.

Heat diffuses itself in all directions.

Light travels only in straight lines.

The colours that absorb and radiate both light and heat do not act in
the same degree upon them both. Black, which does not radiate light, is
a good _radiator of heat_, &c., &c.

The oxy-hydrogen _light_ emits a most intense heat, but glass which
will transmit the rays of light, will afford no passage to the rays of
the _heat_.

Heat is latent in all bodies, but no satisfactory proof has been found
that light is latent in substances.

These are only a few of the analogies and distinctions that exist
between the two mysterious agents, light and heat. But they are
sufficient to supply the starting points of investigation.

     The importance of the heat that attends the solar rays may be
     illustrated by the experiments performed a few years ago, by
     Mr. Baker, of Fleet-street, London, who made a large burning
     lens, three feet and a half in diameter, and employed another
     lens to reduce the rays of the first to a focus of half an inch
     in diameter. The heat produced was so great that iron plates,
     gold, and stones were _instantly melted_; and sulphur, pitch, and
     resinous bodies, _were melted under water_.

545. _What is the point of heat at which bodies become luminous?_

The point of heat at which the eye begins to discover luminosity has
been estimated at 1,000 deg.

546. _What is the velocity of artificial light?_

The light of a fire, or of a candle, or gas, travels with the same
velocity as the light of the sun,--a velocity which would convey light
eight times round the world while a person could count "one."

547. _At what rate of velocity does the light of the stars travel?_

At the same velocity as all other light. And yet there are stars so
distant that, although the light of the sun reaches the earth in eight
minutes and a half, it requires _hundreds of years_ to bring their
light to us.

[Verse: "What is man, that thou art mindful of him? and the son of
man that thou visitest him?"--PSALM VIII.]

548. _What is the relative intensity of primary and reflected light?_

The intensity of a reflection depends upon the power of the reflecting
surface. But, taking the sun and moon as the great examples of primary
and reflected light, the intensity of the _sun's light_ is 801,072
times _greater than that of the moon_.

549. _What is polarized light?_

_Polarized light_ is light which has been subjected to _compound
refraction_, and which, after polarization, exhibits a new series of
phenomena, differing materially from those that pertain to the primary
conditions of light.

550. _What are the chief deductions from the phenomena observed under
the polarization of light?_

The polarization of light appears to confirm in a high degree the
vibratory _theory of light_; and to show that the vibrations of light
have two planes or directions of motion. The mast of a ship, for
instance, has two motions: it progresses _vertically_ as the ship is
impelled forward, and it rolls _laterally_ through the motion of the
billows.

Something like this occurs in the vibrations of light, only the
_vertical vibration_ is the condition of _one ray_, and the _lateral
vibration_ is the condition of another ray, and the vibrations of
these two rays intersect each other in the solar ray. When these
vibrations occur together, the ray has certain properties and powers.
But by polarization the rays may be _separated_, and the result is two
distinct rays, having _different vibrations_.

It then appears that various bodies are transparent to these polarized
rays _only in certain directions_. And this fact is supposed to
show that bodies are made up of their atoms arranged in certain
planes, through or between which the _lateral_ or the _vertical_
waves of light, together or singly, can or cannot pass; and that the
transparency or the opacity of a body is determined by the _relation of
its atomic planes_ to _the planes of the vibrations of light_.

_Ordinary light_, passing through transparent media, produces no very
remarkable effect in its course; but _polarized light_ appears to
illuminate every atom of the permeated substance, and by surrounding it
with a prismatic clothing, to afford an illustration of its _molecular
arrangement_.

[Verse: "A man that is called Jesus made clay, and anointed mine
eyes, and said unto me, Go to the pool of Siloam, and wash: and I went
and washed, and I received sight."--JOHN IX.]

551. _Why are two persons able to see each other?_

Because rays of light _flow from their bodies to each other's eyes_,
and convey an impression of their respective conditions.

     In some popular works that have come under our notice, we find
     that the student is told that "we cannot absolutely see each
     other--we only _see the rays of light reflected from each other_."
     The statement is erroneous as expressed. We do not see the
     _rays_ of light, for if we did so, the effect of vision would
     be destroyed, and all bodies would _appear_ to be in a state of
     _incandesence_, or of _phosphoresence_. Rays of light, which are
     in themselves _invisible_, radiate from the objects we look upon,
     enter the pupil of the eye, and impress the seat of vision in a
     manner which conveys to the mind a knowledge of the form, colour,
     and relative size and position of the figure we look upon. If
     this is not seeing the object--_what is_? It would be just as
     reasonable to say, that we cannot _hear_ a person speak--that we
     only hear the _vibrations of the air_. But as the vibrations are
     imparted to the air by the organs of voice of the speaker, as he
     sets the air in motion, and makes the air his messenger to us, we
     certainly hear _him_, and can dispense with any logical myths that
     confound the understanding, and contribute to no good result.

552. _What is actinism?_

_Actinism_ is the chemical property of light.

     _Actinism_--ray power.

553. _Why does silver tarnish when exposed to light?_

Because of the _actinic_, or chemical power of the rays of the sun.

554. _Why do some colours fade, and others darken, when exposed to the
sun?_

Because of the _chemical_ power of the sun's rays.

555. _Why can pictures be taken by the sun's rays?_

Because of the actinic powers that accompany the solar light.

556. _What is the particular chemical effect of light exhibited in the
production of photographic pictures?_

Simply the _darkening of preparations of silver, by the actinic rays_.

557. _Why are photographic studios usually glazed with blue glass?_

Because blue glass obstructs many of the luminous rays, but it is
perfectly transparent to _actinism_.

[Verse: "The hay appeareth, and the tender grass showeth itself, and
herbs of the mountain are gathered."--PROV. XXVII.]

558. _Why do plants become scorched under the unclouded sun?_

Because the heat rays are in excess. The clouds shut off the scorching
light; but, like the blue glass of the photographer's studio, they
transmit _actinism_.

559. _What effect has actinism upon vegetation?_

It quickens the germination of seeds; and assists in the formation of
the colouring matter of leaves. Seeds and cuttings, which are required
to germinate quickly, will do so under the effect of blue glass (which
is equivalent to saying, the effect of an increased proportion of
_actinism_), in half the time they would otherwise require.

560. _In what season of the year is the actinic power of light the
greatest?_

In the _spring_, when the germination of plants demands its vitalising
aid. In _summer_, when the maturing process advances, _light_ and
_heat_ increase, and _actinism_ relatively declines. In the _autumn_,
when the ripening period _arrives_, _light_ and _actinism_ give way to
a greater ratio of _heat_.

[Verse: "But as it is written, Eye hath not seen, nor ear heard,
neither have entered into the heart of man, the things which God hath
prepared for them that love him."--CORINTH. BOOK I., II.]

     We shall have frequently, in the progress of our lessons, to refer
     to _light_ in its connection with the chemistry of nature, and
     with organic life. But let us now invite the student to pause, and
     for a moment contemplate the wonders of a sunbeam. How great is
     its velocity--how vast its power--how varied its parts--yet how
     ethereal! First, let us contemplate it as a simple beam in which
     _light_ and _heat_ are associated. How deep the darkness of the
     night, and how that darkness clings to the recesses of the earth.
     But the day beams, and darkness flies before it, until every atom
     that meets the face of day is lit up with radiance. That which
     before lay buried in the shade of night is itself now a radiator
     of the luminous fluid. Mark the genial warmth that comes as the
     sister of light; then stand by the side of the experimentalist and
     watch the point on which he directs the shining focus, and in an
     instant see iron melt and stones run like water, under the fervent
     heat! Now look upward to the heavens, where the falling drops of
     rain have formed a natural prism in the rainbow, and shown that
     the beam of pure whiteness, refracted into various rays, glows
     with all the tints that adorn the garden of nature. These are the
     visible effects of light. But follow it into the crust of the
     earth, where it is, by another power, which is neither light nor
     heat, quickening the seed into life; watch it as the germ springs
     up, and the plant puts forth its tender parts, touching them from
     day to day with deeper dyes, until the floral picture is complete.
     Follow it unto the sea, where it gives prismatic tints to the
     _anemone_, and imparts the richest colours to the various _algae_.
     Think of the millions of pictures that it paints daily upon the
     eyes of living things. Contemplate the people of a vast city when,
     attracted by some floating toy in the air, a million eyes look
     up to watch its progress. The sun paints a million images of the
     same object, and each observer has a perfect picture. It makes
     common to all mankind the beauties of nature, and paints as richly
     for the peasant as for the king. The Siamese twins were united
     by a living cord which joined their systems, and gave unity and
     sympathy to their sensations. In the great flood of light that
     daily bathes the world, we have a bond of union, giving the like
     pleasures and inspirations to millions of people at the same
     instant. And that which floods the world with beauty, should no
     less be a bond of unity and love.




CHAPTER XXVII.


561. _What is electricity?_

Electricity is a property of _force_ which resides in all matter, and
which constantly seeks to establish an _equilibrium_.

562. _Why is it called electricity?_

Because it first revealed itself to human observation through a
substance called, in the Greek language, _electrum_. This substance is
known to us as _amber_.

563. _In what way did electrum induce attention to this property of
force in matter?_

Thales, a Greek philosopher, observed that, by briskly rubbing
_electrum_, it acquired the property of _attracting_ light particles
of matter, which moved towards the amber, and attached themselves to
its surface, evidently under the influence of a _force_ excited in the
amber.

564. _What is amber?_

It is a _resinous_ substance, hard, bitter, tasteless, and glossy.
It has been variously supposed to be a vegetable gum, a fossil, and
an animal product. It is probably formed by a _species of ant_ that
inhabit pine forests. The bodies of ants are frequently found in its
substance.

[Verse: "He made darkness his secret place: his pavilion round about
him were dark waters and thick clouds of the skies."]

565. _Why does the rubbing of a stick of sealing-wax cause it to
attract small particles of matter?_

Because it excites in the sealing wax that _force_ which was first
observed in the _amber_. Sealing-wax, therefore, is called an
_electric_ (_amber-like_) body.

566. _Why do we hear of the electric fluid?_

Simply because the term _fluid_ is the most convenient that can be
found to express our ideas when speaking of the _phenomena of electric
force_. But of the nature of electricity, except through its observed
_effects_, nothing is known.

567. _What substances are electric?_

All substances in nature, from the _metals_ to the _gases_. But they
differ very widely in their electrical qualities.

568. _What is positive electricity?_

Electricity, when it exists, or is excited, in any body, to an amount
which is _in excess_ of the amount natural to that body, is called
_positive_ (called also _vitreous_).

569. _What is negative electricity?_

Electricity, when it exists, or is excited, in any body, in an amount
which _is less_ than is the amount natural to that body, is called
_negative_ (called also _resinous_).

570. _Why is "positive" electricity called also "vitreous," and
"negative" electricity called also "resinous"?_

Because some philosophers believe that there is but _one electricity_,
but that it is liable to variations of _quantity_ or _state_, which
they distinguish by _positive_ and _negative_; while other philosophers
believe that there are _two electricities_, which they name _vitreous_
and _resinous_, because they may be induced respectively from
_vitreous_ and _resinous_ substances, and they display forces of
attraction and repulsion.

571. _Upon what do the electrical phenomena of nature depend?_

Upon the tendency of _electricity_ to find an _equilibrium_ between
its _positive_ and _negative_ states (assuming there to be but _one_
fluid); or upon the tendency of _vitreous electricity_ to seek out
and combine with _resinous electricity_ (assuming that there are _two_
fluids).

[Verse: "The Lord also thundered in the heavens, and the Highest
gave his voice; hailstones and coals of fire."]

572. _How does the equilibrium of electricity become disturbed?_

By changes in the condition of matter. As electricity resides in
all substances, and is, perhaps, an essential ingredient in their
condition, so every change in the state of matter--whether from
heat to cold, or from cold to heat; from a state of rest to that of
motion; from the solid to the liquid, or the æriform condition, or
_vice versa_; or whether substances combine chemically and produce new
compounds--in every change _the electrical equilibrium is disturbed_;
and, in proportion to the degree of disturbance, is the force exerted
by electricity to resume its balance in the scale of nature.

573. _How does electricity seek to regain equilibrium?_

By passing through substances that are favourable to its diffusion;
therefore they are called _conducting_ or _non-conducting_ bodies,
according as they favour or oppose the transmission of the electrical
current.

574. _What substances are conductors of electricity?_

Metals, charcoal, animal fluids, water, vegetable bodies, animal
bodies, flame, smoke, vapour, &c.

575. _What substances are non-conductors?_

Rust, oils, phosphorous, lime, chalk, caoutchouc, gutta percha,
camphor, marble, porcelain, dry gases and air, feathers, hair, wool,
silk, glass, transparent stones, vitrefactions, wax, amber, &c. These
bodies are also called _insulators_. Some of these substances, as
chalk, feathers, hair, wool, silk, &c., though non-conductors when
_dry_, become conductors when _wetted_.

     _Insulating_--preventing from escaping.

576. _Why are amber and wax classed among the non-conductors, when they
have been pointed out as electrics, and used to illustrate electrical
force?_

It is _because_ they are _non-conductors_ that they have displayed,
under excitement, the attractive force shown in respect to the
particles of matter which were drawn towards their substances. If a bar
of _iron_ were excited, instead of a stick of wax, electricity would be
equally developed; but the iron, _being a good conductor_, would pass
the electricity to the hand of the operator as fast as it accumulated,
and the equilibrium would be undisturbed.

[Verse: "Yea, he sent out his arrows, and scattered them; and he
shot out lightnings and discomfited them."--PSALM XVIII.]

577. _What is the effect when electricity, in considerable force, seeks
its equilibrium, but meets with insulating bodies?_

The result is a violent action in which, _intense heat and light_ are
developed, and in the evolution of which _the electric force becomes
expended_.

578. _What is the cause of electric sparks?_

The electric force, passing through a conducting body to find its
_equilibrium_, is checked in its course by an insulator, and emits a
spark.

579. _What produces the electric light?_

Currents of electricity pass towards each other along wires at the ends
of which two charcoal points are placed. As long as the charcoal points
remain in contact, the electric communication is complete, and no light
is emitted, but, when they are drawn apart, intense heat and light are
evolved.

[Illustration: Figs. 17 & 18.--SHOWING THE EFFECT OF THE UNION AND THE
SEPARATION OF THE CHARCOAL POINTS.]

580. _What is the cause of lightning?_

Lightning is the result of _electrical discharges_ from the _clouds_.

581. _What develops electricity in the clouds?_

Evaporations from the surface of the earth; changes of temperature in
the atmospheric vapour; chemical action upon the earth's surface; and
the friction of volumes of air of different densities against each
other.

[Verse: "His lightnings enlightened the world: the earth saw and
trembled."--PSALM XCVII.]

582. _Why do these phenomena produce electricity?_

Because they disturb the equilibrium of the electric force, and produce
_positive_ and _negative_ states of electricity.

583. _When does lightning occur?_

When clouds, charged with the _opposite electricities_ approach, the
forces rush to each other, and combine in a state of equilibrium.

584. _Why does lightning attend this movement of the forces of
electricity?_

Because the atmosphere, being unable to convey the great charges of
electricity as they rush towards each other, _acts as an insulator_,
and lightning is caused by the _violence of the electricity in forcing
its passage_.

585. _Does lightning ever occur when the conducting power is equal to
the force of the electricity?_

No; electricity passes invisibly, noiselessly, and harmlessly, whenever
it finds a sufficient source of _conduction_.




CHAPTER XXVIII.


586. _Why does lightning sometimes travel through a "zigzag" course?_

Because the electricity, being resisted in its progress by the air,
_flies from side to side_, to find the readiest passage.

587. _Why does lightning sometimes appear forked?_

Because, being resisted in its progress by the air, the electricity
divides into two or more points, and _seeks a passage in different
directions_.

588. _Why is lightning sometimes like a lurid sheet?_

Because the flash is distant, and therefore we see only the
_reflection_.

[Verse: "He directeth it under the whole heavens, and his lightning
unto the ends of the earth."]

589. _When is the flash of lightning straight?_

When the distance between the clouds whose electricities are meeting,
is small.

590. _What is the cause of the aurora borealis?_

The _mingling of the electricities_ of the higher regions of the
atmosphere.

591. _When does the flash of lightning appear blue?_

When the degree of electrical excitement is intense, and _general
throughout the atmosphere_.

592. _Why does lightning sometimes appear red, at others yellow, and at
others white?_

Because of the varying humidity, which affects the _refracting power_
of the atmosphere.

593. _Does lightning ever pass upwards from the earth to the clouds?_

Yes; when the earth is charged with a _different electricity_ to that
which is in the clouds.

594. _Does lightning ever pass directly from the clouds to the earth?_

Yes; when the electricity of the clouds seeks to combine with the
_different electricity_ of the earth.

     The mingling of the electricities of the earth and the air must
     be continually going on. But _lightning_ does not attend the
     phenomena, because all natural bodies, vapours, trees, animals,
     mountains, houses, rocks, &c., &c., act more or less as conductors
     between the earth and the air. It is only when there is a great
     disturbance of the electrical forces, that _terrestrial lightning_
     is developed. When lightning strikes the earth with great force,
     it sometimes produces what are called _fulgurites_ in sandy soils;
     these are hollow tubes, produced by the melting of the soil.

595. _What is the extent of mechanical force of lightning?_

Lightning has been proved, in one instance, to have struck a church
with a force equal to more than 12,000 horse-power. A single
horse-power, in mechanical calculations, is equivalent to raising a
weight of 32,000 lbs. one foot in a minute. The force of lightning,
therefore, has been proved to be equal to the raising of 384,000,000
lbs. one foot in a minute. This is equal to the united power of
twelve of our largest steamers, having collectively 24 engines of 500
horse-power each. The velocity of electricity is so great that it would
travel round the world _eight times in a minute_.

[Verse: "After it a voice roareth: he thundereth with the voice
of his excellency; and he will not stay them when his voice is
heard."--JOB XXXVII.]

     The church alluded to was St. George's church, Leicester, a new
     edifice, which was completely destroyed on the 1st of August,
     1846, by a thunder-storm. The steeple was rent asunder, and
     massive stones were hurled to a distance of thirty feet. The
     vane rod and top part of the spire fell down perpendicularly and
     carried with it all the floors of the tower. A similar disaster
     occurred to St. Bride's church, Fleet-street, London, about 100
     years ago. The lightning first struck upon the metal vane of the
     steeple, and then ran down the rod and attacked the iron cramps,
     smashing the large stones that lay between them. The church was
     nearly destroyed. By the same wonderful force, ships have been
     disabled, trees split asunder, houses thrown down, and animals
     struck dead.

596. _Why is it dangerous to stand near a tree during an electric
storm?_

Because the tree is a _better conductor than air_, and electricity
would probably strike the tree, and then pass to the person standing
near.

597. _If trees are good conductors, why do they not convey the
electricity to the ground?_

Trees are only _indifferent conductors_, and the electricity would quit
the tree to pass through any _better conductor_.

598. _Why is it dangerous to sit near a fire during an electric storm?_

Because the chimney, being _a tall object_, and smoke a _good
conductor_, would probably attract the electricity, and convey it to
the body of a person sitting near the fire.

599. _Why is it dangerous to be near water during an electric storm?_

Because water is a _good conductor_, and the vapour arising from it
might attract the electricity. Man, _being elevated over the water_,
might form the first point attacked by the electricity.

600. _Are iron houses dangerous during an electric storm?_

No; they are _very safe_, because their entire surface is a good
conductor, and would convey the electricity harmlessly to the earth.

[Verse: "To him that rideth upon the heavens of heavens, which
were of old; lo, he doth send out his voice, and that a mighty
voice."--PSALM LXVIII.]

601. _Why does electricity seize upon bell wires and iron fastenings?_

Because copper wires are the _very best_ conductors of electricity; and
iron articles are also good conductors.

602. _Supposing electricity to attack a bell wire, where would the
point of danger exist?_

At the _extremities of the wire_, where the conducting power of the
wire would cease, and the electricity would seek to find _another
conductor_.

603. _Are umbrellas, with steel frames, dangerous in an electric storm?_

They are dangerous _in some degree_, because they might convey
electricity to the hand, and then transfer it to the body. But,
generally speaking, when it rains, the rain itself, _being a good
conductor_, relieves the disturbance of electricity by conveying it to
the ground.

604. _Are iron bedsteads dangerous in electric storms?_

No, they are safe, because the iron frame, completely surrounding the
body, and having _a great capacity for conduction_, would keep the
electricity away from the body.

605. _Why is it safe to be in bed during an electric storm?_

Because _feathers_, _hair_, _wool_, _cotton_, &c., especially when dry,
are good _insulators_ or _non-conductors_.

606. _What is the safest situation to be in during an electric storm?_

In the centre of a room, _isolated_ as far as possible from surrounding
objects; sitting on a chair, and avoiding handling any of the
conducting substances. The windows and doors should be closed, to
prevent _drafts of air_.

607. _In the open air, what is the safest situation?_

To keep aloof, as far as possible, from elevated structures; and
regard the rain, though it might saturate our clothes, as a protection
against the lightning stroke, for _wet clothes_ would supply so _good
a conductor_, that a large amount of electricity would pass over man's
body, through wet garments, and he would be quite unconscious of it.

[Verse: "God thundereth marvellously with his voice: great things
doeth he, which we cannot comprehend."--JOB XXXVI.]

     During a violent electric storm in the Shetland Islands, a fishing
     boat was attacked by the electric fluid, which tore the mast to
     shivers. A fisherman was sitting by the side of the mast at the
     time, but he felt no shock. Upon taking out his watch, however, he
     found that the electric current had actually fused his watch into
     a mass. In this case, it is more than probable that the man was
     saved through the saturation of his clothes with rain.

608. _Do lightning conductors "attract" electricity?_

Not unless the electric current lies in their vicinity.

609. _Why have lightning conductors sometimes been found ineffective?_

Because they have been unskilfully constructed; have been too small
in their dimensions, and have not been properly laid to convey the
electricity harmlessly away.

610. _What is the best metal for a lightning conductor?_

_Copper_, the conducting power of which is _five times greater than
that of iron_.

611. _Why should a large building have several conductors?_

Because the influence of a conductor over the electricity of the
surrounding air does not extend to more than a radius of double the
height of the conductor above the building: for instance, a conductor
rising _ten feet high_ above the building would influence the
electricity _twenty feet all round the conductor_.

612. _Why should conductors have at their base several branches
penetrating the earth?_

To facilitate the discharge of the _accumulated electricity_ into the
earth.

613. _Why does electricity affect the shapes of clouds?_

Because electricity does not penetrate the _masses_ of _bodies_, but
affects generally _their surfaces_. Hence electricity exists in the
_surfaces of clouds_, and in its efforts to _find an equilibrium_ it
causes the clouds to roll in _heavy masses_, having dark outlines.

[Verse: "All ye inhabitants of the world, and dwellers on the earth,
see ye, when he lifteth up an ensign on the mountains; and when he
bloweth a trumpet, hear ye."--ISAIAH XVIII.]

     The fact that electricity resides in, and is conducted by, the
     _surfaces_ of bodies, is well established, and should receive due
     attention in the protective measures adopted to secure life and
     property against the effects of lightning. A practical suggestion
     that arises out of this fact is, that _tubes of copper_ would
     form far more efficient conductors than _bars_ of the same metal.
     A _copper tube_, of half an inch diameter, would conduct _nearly
     double_ the amount of electricity which could be conveyed away by
     a _bar_ of copper of the same diameter. The upper extremity of the
     tube should be open obliquely, that the electric current might be
     induced to pass over _both the inner and outer surfaces_.




CHAPTER XXIX.


614. _What is thunder?_

Thunder is the _noise which succeeds the rush_ of the electrical fluid
through the air.

615. _Why does noise follow the commotion caused by electricity?_

Because, by the violence of the electric force, vast _fields of air
are divided_; great volumes of air are _rarefied_; and _vapours_ are
_condensed_, and thrown down as _rain_. Thunder is therefore caused by
the _vibrations of the air_, as it collapses, and seeks to restore its
own _equilibrium_.

616. _Why is the thunder-peal sometimes loud and continuous?_

Because the electrical discharge takes place near the hearer, and
therefore the vibrations of the air are heard in their full power.

617. _Why is the thunder-peal sometimes broken and unequal?_

Because the electrical discharge takes place at a _considerable
distance_, and the vibrations are affected in their course by
_mountains_ and _valleys_. Because, also, the _forked arms_ of the
lightning strike out in different directions, causing the sounds of
thunder to reach us from _varying distances_.

[Verse: "Lo, these are parts of his ways; but how little a portion
is heard of him? but the thunder of his power who can understand?"--JOB
XXV.]

618. _Why has the thunder-peal sometimes a low grumbling noise?_

Because the electrical discharges, though violent, take place _far
away_, and the vibrations of the air _become subdued_.

619. _Why does the thunder-peal sometimes follow immediately after the
flash of lightning?_

Because the discharge of electricity takes place near the hearer.

620. _Why does the thunder-peal sometimes occur several seconds after
the flash?_

Because the discharge takes place far away, and _light_ travels with a
much greater velocity than _sound_.

621. _Through what distance will the sound of thunder travel?_

Some _twenty or thirty miles_, according to the _direction of the
wind_, and the violence of the peal.

622. _Through what distance will the light of lightning travel?_

The _light_ of lightning, and its reflections, will penetrate through a
distance of from _a hundred and fifty to two hundred miles_.

623. _How may we calculate the distance at which the electric discharge
takes place?_

Sound travels at the rate of _a quarter of a mile in a second_. If,
therefore, the peal of thunder is heard _four seconds_ after the flash
of lightning, the discharge took place about a mile off. The pulse
of an adult person beats about _once in a second_; therefore, guided
by the pulse, any person may calculate the probable distance of the
storm:--

      2 beats, 1/2 a mile.
      3 beats, 3/4 of a mile.
      4 beats, 1 mile.
      5 beats, 1-1/4 miles.
      6 beats, 1-1/2 miles.
      7 beats, 1-3/4 miles.
      8 beats, 2 miles, &c.

Attention should be paid to the _direction and speed of the wind_, and
some modifications of the calculation be made accordingly. Persons
between 20 and 40 years of age should count _five beats of the pulse to
a mile_; under 20, _six beats_.

[Verse: "The clouds poured out water; the skies sent out a sound;
thine arrows also went abroad."]

624. _Why are electric storms more frequent in hot than in cold
weather?_

Because of the _greater evaporation_, as the effect of heat; and also
of the _effect of heat_ upon the particles of all bodies.

625. _Why do electric storms frequently occur after a duration of dry
weather?_

Because _dry air_, being a bad conductor, prevents the _opposite
electricities_ from finding their _equilibrium_.

626. _Why is a flash of lightning generally succeeded by heavy rain?_

Because the electrical discharge destroys the _vescicles_ of the
vapours. If a number of _small soap-bubbles_ floating in the air were
_suddenly broken_ by a violent commotion of the atmosphere, the _thin
films_ of the bubbles would form _drops of water_, and fall _like rain_.

627. _Why is an electrical discharge usually followed by a gust of
wind?_

Because the equilibrium of the atmosphere is disturbed by the _heat
and velocity of lightning_, and the _condensation of vapour_. Air,
therefore, rushes towards those parts where a degree of _vacuity_ or
_rarefaction_ has been produced.

628. _What is a thunderbolt?_

The name _thunderbolt_ is applied to an electrical discharge, when the
lightning appears to be developed with the greatest intensity around a
nucleus, or centre, as though it contained a burning body. But there
is, in reality, _no such thing as a thunderbolt_.

[Verse: "The voice of the Lord is upon the waters: the God of glory
thundereth; the Lord is upon many waters."--PSALM XXIX.]

629. _Why do electric storms purify the air?_

Because they restore the _equilibrium of electricity_ which is
essential to the salubrity of the atmosphere; they intermix the _gases
of the atmosphere_, by agitation; they _precipitate the vapours_
of the atmosphere, and with the precipitation of vapours, _noxious
exhalations_ are taken to the earth, where they become absorbed; they
also contribute largely to the formation of _ozone_, which imparts to
the air corrective and restorative properties.

630. _What is ozone?_

Ozone is an _atmospheric element_ recently discovered, and respecting
which differences of opinion prevail. It is generally supposed to be
_oxygen_ in a state _of great strength_, constituting a variety of form
or condition.

631. _Why do we know that electricity contributes to the formation of
ozone?_

Because careful observations have established the fact that the
proportion of _ozone_ in the atmosphere is _relative to the amount of
electricity_.

632. _What are the properties of ozone?_

It displays an extraordinary power in the neutralisation of
putrefactions, rapidly and thoroughly counteracting noxious
exhalations; it is the most powerful of all _disinfectants_.

     Schonbien, the discoverer of _ozone_, inclines to the opinion
     that it is a _new chemical element_. Whatever it may be, there
     can be no doubt that it plays an important part in the economy of
     nature. Its _absence_ has been marked by pestilential ravages, as
     in the _cholera_ visitations; and to its _excess_ are attributed
     epidemics, such as _influenza_. It was found, during the last
     visitation of cholera, that the _fumigation of houses with
     sulphur_ had a remarkable efficacy in preventing the spread of
     the contagion. The combustion of sulphur ozonised the atmosphere;
     the same result occurs through the emission of _phosphoric
     vapours_; ozone is also developed by the electricity evolved by
     the _electrical machine_, and in the greater _electrical phenomena
     of nature_. The smell imparted to the air during an electric
     storm is identical with that which occurs in the vicinity of an
     electrical apparatus--it is a _fresh_ and _sulphurous_ odour. The
     opinion is gaining ground that the respiration of animals and the
     combustion of matter are sources of ozone, and that plants produce
     it when under the influence of the direct rays of the sun. It is
     also believed to be produced by water, when the sun's rays fall
     upon it. The most recent opinion respecting ozone is, that it is
     _electrized oxygen_. The subject is of vast importance, and opens
     another field of discovery to the pioneers of scientific truth.

[Verse: "The voice of thy thunder was in the heaven: the lightnings
lightened the world, the earth trembled and shook."--PSALM LXVII.]

633. _What is magnetism?_

_Magnetism_ is _the electricity of the earth_, and is characterised by
the circulation of _currents of electricity passing through the earth's
surface_.

634. _What are magnetic bodies?_

Magnetic bodies are those that exhibit phenomena which show that
they are under the influence of _terrestrial electricity_, and which
indicate the direction of the _poles_, or _extreme points_, _of
magnetic force_.

635. _What is Galvanism?_

Galvanism is the action of _electricity upon animal bodies_, and is so
called from the name of its first discoverer, Galvani.

636. _What is Voltaic electricity?_

Voltaic electricity is the electricity that is developed during
_chemical changes_, and is so called after Volta, who enlarged upon the
theory of Galvani.

637. _What are the differences between mechanical, or frictional
electricity, Voltaic electricity, Galvanism, and magnetism?_

_Frictional_ electricity is electricity _suddenly_ liberated under the
effects of the _motion_, or the mechanical disturbance of bodies.

_Voltaic_ electricity is a _steady flow_ of an electric current,
arising from the _gradual changes_ of _chemical_ phenomena.

_Galvanism_ and _Voltaism_ are almost _identical_, since the latter
is founded upon, and is a development of, the former. But the term
_Galvanism_ is frequently used when speaking of the development of
electricity in _animal bodies_.

_Magnetism_ is the electricity of the _earth_, and is understood to
imply the _fixed electricity of terrestrial bodies_.

[Verse: "And I heard as it were the voice of a great multitude, and
as the voice of many waters, and as the voice of mighty thunderings,
saying Alleluia: for the Lord God omnipotent reigneth."--REV. XIX.]

     Man knows not _what electricity is_; yet, by an attentive
     observance of its _effects_, he avails himself of the power
     existing in an unknown source, and produces marvellous results.
     When the Grecian philosopher, Thales, sat rubbing a piece of
     amber, and watching the attraction of small particles of matter
     to its surface, he little knew of the mighty power that was then
     whispering to him its offer to serve mankind. And when Franklin,
     with the aid of a boy's plaything, drew down an electric current
     from the clouds, and caught a spark upon the knuckles of his hand,
     _even he_ little conjectured that the time was so near when that
     strange element, which sent its messenger to him along the string
     of a kite, would become one of man's most submissive servants.

     So many great results have sprung from the careful observation
     of the simplest phenomena, that we should never pass over
     inattentively the most trifling thing that offers itself to our
     examination. Nature, in her revelations, never seeks to _startle_
     mankind. The formation of a rock, and the elaboration of a truth,
     are alike the work of ages. It was the simple blackening of silver
     by the sun's rays which led to the discovery of the _chemical
     agency of light_. It was the falling of an apple which pointed
     Newton to the discovery of the _laws of gravitation_. It was the
     force of steam, observed as it issued from beneath the lid of a
     kettle, that led to the invention of the _steam-engine_. And it is
     said of Jacquard, that he _invented the loom_ which so materially
     aided the commerce of nations, while watching the motions of his
     _wife's fingers_, as she plied her knitting. As great discoveries
     spring from such small beginnings, who among us may not be the
     herald of some great truth--the founder of some world-wide
     benefaction?

     That the area of discovery has not perceptibly narrowed its
     limits, is evident from the fact that the greatest elements in
     nature are still mysteries to man. And though it may not be within
     the power of a finite being to unravel the chain of wonders that
     enfold the works of an infinite God,--still it is evident, from
     the progress which discovery has made, and from the good which
     discovery has done, that God _does_ invite and encourage the human
     mind to contemplate the workings of Divine power, and to pursue
     its manifestations in every element, and in every direction.

     The wonderful force of _electricity_ astonishes us all the more
     when we view it in contrast with that equally wonderful element,
     _light_. We have seen that light travels with a velocity of
     192,000 miles in a second, but that it falls upon a delicate
     balance so gently, that it produces no perceptible effect. As far
     as we know the nature of _electricity_, it is even _more ethereal_
     than _light_; yet, while the _ether of light_ falls harmlessly and
     imperceptibly--even with the momentum of a flight of _ninety-five
     millions of miles_, the _ether of electricity_, bursting from
     a cloud only _five hundred yards_ distant, will split massive
     stones, level tall towers with the dust, strike majestic trees
     to the ground, and instantly extinguish the life of man! _Why_
     does _the one ether_ come divested of all mechanical force, while
     that which seems to be _even more ethereal_ than it, is capable
     of exerting the mightiest force over material things? Does it not
     appear that the Creator of the universe has established these
     paradoxes of power to testify his Omnipotence--to show to man that
     with Him all things are possible; and that, in the grand cosmicism
     of the universe, every attribute of Omnipotence has been fulfilled?

[Verse: "And the seventh angel poured out his vial into the air; and
there came a great voice out of the temple of heaven, from the throne,
saying, It is done."--REV. XVI.]

     Let us now consider man's relation to this Omnipotence. He sees
     that electricity smites the tall edifice, and observes that in
     doing so it displays a choice of a certain substance through
     which it passes harmlessly, and that its violence is manifested
     only when its path is interrupted. Man, taking advantage of this
     preference of electricity for a particular conductor, stretches
     out an arm of that substance, and points it upwards to the
     clouds; electricity accepts the invitation, and passes harmlessly
     to the earth. But this not all: man learns by observation that
     electricity resides in all matter; that it may be collected or
     dispersed; that it travels along a good conductor at the rate
     of _half-a-million of miles in a second of time_; he constructs
     a battery, a kind of scientific fortress, in which he encamps
     the great warrior of nature; and then, laying down a conducting
     wire, he liberates the mighty force: but its flight must be on
     the path which man has defined, and its journey must cease at the
     terminus which man has decreed, where, by a simple contrivance of
     his ingenuity (the movements of a magnetic needle), the electric
     current is made to deliver whatever message of importance he
     desires to convey. Thus, the element which in an instant might
     deprive man of life, is subdued by him, and made the obedient
     messenger of his will.




CHAPTER XXX.


638. _What is the atmosphere?_

The _atmosphere_ is the transparent and elastic body of mixed gases
and vapours which envelopes our globe, and which derives its name from
Greek words, signifying _sphere_ of _vapour_.

639. _To what height does the atmosphere extend?_

It is estimated to extend to from _forty to fifty miles_ above the
surface of the earth.

640. _Why is it supposed that the atmosphere does not extend beyond
that height?_

Because it is found, by experiment and observation, that the air
becomes _less dense_ in proportion to its altitude from the earth's
surface. The gradual decrease of atmospheric density observed in
ascending a mountain, or in a balloon, supplies sufficient data to
enable us to calculate the height at which the atmosphere would
probably _altogether cease_.

     At an altitude of 18,000 feet the air is indicated by the
     barometer to be only _half as dense_ as at the surface of
     the earth. And as the densities of the atmosphere decrease
     in a geometrical progression, the density will be reduced to
     _one-fourth_ at the height of 36,000 feet; and to _one-eighth_
     at 54,000 feet. The effects of the decreasing density of the
     atmosphere are, that the _intensity of light and sound are
     diminished, and the temperature is lowered_. Persons who have
     reached a very high elevation, state that the sky above them began
     to assume the appearance of darkness; and there can be no doubt
     that, if it were possible to reach an altitude of some fifty to
     sixty miles, there would be _perfect blackness although the sun's
     rays might be pouring through the darkened space_, to illuminate
     the atmosphere. Upon the summit of Mont Blanc, the report of a
     pistol at a short distance can _scarcely be heard_. When Gay
     Lussac reached the height of 23,000 feet, he breathed with great
     pain and difficulty, and felt distressing sensations in his ears,
     as though they were _about to burst_. Upon the high table-lands of
     Peru, the lips of Dr. Ischudi cracked and burst; and blood flowed
     from his eyelids.

[Verse: "For he looketh to the ends of the earth, and seeth under
the whole heaven; To make the weight for the winds."--JOB XXVIII.]

641. _What is the amount of atmospheric pressure at the earth's
surface?_

The pressure of the atmosphere at the earth's surface is _fifteen
pounds_ to every square inch of surface. That is to say, that the
column of air, extending fifty miles over a square inch of the earth,
presses upon that square inch with a weight equal to _fifteen pounds_.

642. _Is that the weight of dry or moist air?_

That is the weight of air at what is called the _point of saturation_,
when it is fully charged with _watery vapour_.

643. _What is the proportion of watery vapour in the atmosphere?_

The proportion _constantly varies_. Evaporation is not a result of
accident; it seems an _established law_ that the air shall constantly
_absorb vapour_ until it has reached the maximum that it can hold.
Experiments have been tried, in which dry air has been pressed upon the
surface of water with great force, _but no degree of pressure could
prevent the formation of vapour_. (_See_ 431.)

644. _What is the total amount of atmospheric pressure on the earth's
surface?_

The total amount of atmospheric pressure on the earth's surface, at 15
lbs. to the square inch, amounts to 12,042,604,800,000,000,000 lbs.
This pressure is equal to that of a globe of lead of _sixty miles in
diameter_.

645. _What is the pressure of the atmosphere upon the human body?_

Estimating the surface of man's body to be equal to _fifteen square
feet_, he sustains an atmospheric pressure of 32,400 lbs., or nearly
_fourteen tons and a-half_. The mere _variation of weight_, arising
out of the changes in the state of the atmosphere, may amount to as
much as a _ton and a-half_.

[Verse: "I therefore so run, not as uncertainly; so fight I, not as
one that beateth the air."--CORINTH. IX.]

646. _Why does not man feel this pressure?_

Because the diffusion of air which, _surrounding him in every
direction_, and acting upon the _internal_ as well as the _external_
surfaces of his body, and probably _surrounding every atom of his
frame_, establishes an equilibrium, in which every degree of pressure
_counteracts and sustains itself_.

647. _What is the weight of air relative to that of water?_

A cubic foot of air weighs only 523 grains, a little more than _an
ounce_; a cubic foot of water weighs _one thousand ounces_.

648. _What is the greatest height in the atmosphere which any human
being has ever reached?_

M. Gay Lussac, in the year 1804, ascended to the height of 23,000 feet.

649. _What is a vacuum?_

A vacuum is a space _devoid of matter_. The term is generally applied
to those instances in which air is drawn from within an air-tight
vessel.

650. _Is it possible to form a perfect vacuum?_

It is probably _impossible to do so_, even with the most powerful
instruments--some portion of air would remain, but in so thin a form
that it would be _imperceptible_.

651. _Why does the depression of a pump-handle cause the water to flow?_

Because the putting down of the handle lifts up the piston with its
_valve closed_, thereby tending to produce a _vacuum_; but _the
pressure of the air_ upon the water _not contained in the pump_, forces
more water up into the part where a _vacuum_ would otherwise be formed.
Then, when the handle is raised, and the piston forced downwards, _the
valve opens_, and the water rushes through.

There is a second valve, below the piston, which closes with the
downward movement, to prevent the water from _rushing back again._

[Verse: "The wind bloweth where it listeth, and thou hearest the
sound thereof, but canst not tell whence it cometh, and whither it
goeth: so is every one that is born of the Spirit."--JOHN II., III.]

652. _How high will atmospheric pressure raise water in the bore of a
pump?_

It will raise water to an elevation of _thirty feet_ above its level.

653. _Why will it raise water to an elevation of thirty-feet?_

Because a column of water of _thirty feet high_, nearly balances the
weight of _a column of air_ of equal surface, _extending to the whole
height of the atmosphere_. When, therefore, water is elevated to the
height of thirty feet, the power of the pump is enfeebled, as the air
and the water _balance each other_.

654. _How is water raised to a greater elevation when it is required?_

By mechanical contrivances, by which the water is _forced_ to a greater
elevation.

655. _Why does water run through the bent tube called a syphon?_

Because the atmospheric pressure upon the water on _the outside of the
syphon_ forces it into the tube as fast as the syphon empties itself
through its longer arm.

656. _Why does water run through the longer arm of the syphon?_

Because the weight of the water in the longer arm of the syphon _is
greater than that in the shorter_; therefore it runs out by its own
gravity. And, as in running out, it creates a tendency towards a
_vacuum_, the pressure of the outer air comes into operation, and
forces the water through the tube.

657. _Why does water issue from the earth in springs?_

Some springs are caused by _natural syphons_ formed in the fissures
of rocks, which, communicating with bodies of water, are continually
filled by atmospheric pressure, and therefore convey streams of water
to the point where they are set free.

[Verse: "Ascribe ye strength unto God: his excellency is over
Israel, and his strength is in the clouds."--PSALM LVIII.]

658. _Why, if a wine glass is filled with water, and a card laid upon
it, and the whole inverted, will the water remain in the glass?_

Because the pressure of the atmosphere upon the surface of the card
counteracts the weight of the water.

659. _What has the card to do with the experiment?_

It forms _a base_ upon which the water may rest, while the glass is
being inverted; and it prevents the air from acting upon the _fluidity_
of the water, and forcing it out of the glass.

660. _Why will not beer run out of the tap of a cask until a spile has
been driven in at the top?_

Because the pressure of the air upon the opening of the tap counteracts
the weight of the beer. But when the spile is driven in, the air enters
at the top, _and counteracts its own pressure at the bottom_.

661. _Why does a cup in a pie become filled with juice?_

Because _the heat expands the air_, and drives nearly all of it out of
the cup. When the pie is taken out of the oven, and begins to cool,
air cannot get into the cup again, because its edges are surrounded by
juice. A _partial vacuum_, therefore, exists within the cup, and the
pressure of the external air _forces the juice into it_.

662. _Does the cup prevent the juice from boiling over?_

No. So long as the _heat_ exists, the cup remains _empty_; and as it
occupies space, the air is driven out of it, into the pie, it rather
tends to force the juice over the sides of the dish. It is only _when
cooling_ that the juice enters the cup.

663. _Why can flies walk on the ceiling?_

Because their feet are so formed that they can form a _vacuum_, under
them; their bodies are therefore sustained in opposition to gravitation
by _atmospheric pressure_.

664. _How did Mr. Sands perform the feat of walking across the ceiling?_

By having large discs of wet leather attached to his feet, so that
when they were placed upon a smooth surface, the air was excluded, and
when he allowed his weight to act upon one of the discs, it formed a
_hollow cup_ and a _vacuum_. By forming a vacuum of only _twelve square
inches_ he gained a pressure of 180 lbs.; this being more than his
weight he could accomplish the feat with no other difficulty than that
of remaining in an inverted position. The air was admitted underneath
the discs by valves, which were closed by springs, which being pressed
by the heels of the performer, let in the air, and _set the feet free_.

[Verse: "And God made a wind to pass over the earth."--GENESIS VIII.]

665. _Why is it difficult to strike limpets from rocks?_

Because they have the means of forming a _vacuum_ under their shells,
and are pressed on to the rocks by the weight of the atmosphere.

666. _Why can snails move over plants in an inverted position?_

Because they form a _vacuum_ with the smooth and moist surfaces of
their bodies, and are supported by atmospheric pressure.




CHAPTER XXXI.


666. _What is wind?_

Wind is air _in motion_. (_See_ 234.)

667. _What are the velocities of winds?_

A _breeze_ travels ten feet in a second; a _light gale_, sixteen feet
in a second; a _stiff gale_, twenty-four feet in a second; a _violent
squall_, thirty-five feet in a second; _storm wind_, from forty-three
to fifty-four in a second; _hurricane_ of the temperate zone, sixty
feet in a second; _hurricane_ of the torrid zone, one hundred and
twenty to three hundred feet in a second. When wind flies at one mile
an hour, it is scarcely perceptible. When its velocity is one hundred
miles an hour, it tears up trees, and devastates its track.

668. _What are trade winds?_

Trade winds are vast currents of air, which _sweep round the globe_
over a belt of some 12,000 miles in width.

[Verse: "They shall be as the morning cloud, and as the early dew
that passeth away, as the chaff that is driven with the whirlwind out
of the floor, and as the smoke out of the chimney."--HOSEA XIII.]

669. _What is the cause of trade winds?_

The air over the tropical regions becomes heated and ascends; it then
diverges in two high currents, one towards the north, and the other
towards the south pole, where, being cooled, it again descends, and
returns towards the equator to replace the air as it ascends therefrom.
There is, therefore, a constant revolution of vast currents of air
between the tropics and the poles, producing _north and south winds_.

670. _Why do the trade winds blow from east to west, though, in their
origin, their direction is from north to south and from south to north?_

Because, as the north and south winds blow towards the equator, they
are affected by the revolution of the earth from _west to east_. As
the two winds from the poles approach the equator, they are gradually
diverted from their northerly and southerly course, to an easterly
direction, by the revolution of the earth.

671. _Why is there a prevalence of calms at the equator?_

Because, as the north and the south winds move towards the equator,
they drive before them volumes of atmosphere, which, meeting in
opposite directions, resist and counterpoise each other, and abide in a
state of stillness between the north and south-easterly winds, one on
the north and the other on the south of the equator.

672. _What are monsoons?_

Monsoons are _periodical winds_ which blow at a given period of the
year from one quarter of the compass, and in another period of the year
from the opposite quarter of the compass.

673. _What is the cause of monsoons?_

Monsoons are caused by changes in the position of the sun. When the
sun is in the southern hemisphere, it produces a _north-east wind_,
and when it is in the northern hemisphere, a _north-west wind_. The
north-east monsoon blows from November to March, and the south-west
monsoon from the end of April to the middle of October. The region of
monsoons lies a little to the north of the northern border of the trade
wind, and they blow with the greatest force, and with most regularity,
between the eastern coast of Africa and Hindustan.

[Verse: "He shall blow upon them and they shall wither, and the
whirlwind shall take them away as stubble."--ISAIAH XL.]

674. _What determines the character of winds?_

The character of winds is influenced by the condition of _the surfaces
over which they blow_. Winds blowing over dry and arid plains and
deserts are _dry and hot_. Winds blowing across snow-capped mountains
and regions of ice are _cold_. Winds that cross oceans are _wet_; and
those that cross extensive continents are _dry_.

675. _What winds are most prevalent in England?_

In England out of a _thousand days_, north winds prevail in 82;
north-east, 111; east, 99; south-east, 81; south, 111; south-west, 225;
west, 171; north-west, 120.

676. _What is the cause of storms?_

Storms result from violent commotions of the atmosphere, and are
chiefly the result of extreme _changes of temperature_.

The _magnetic_ state of the earth, and the _electrical_ state of the
atmosphere, also materially influence the phenomena of storms.

By some persons the theory is entertained that storms result from
various winds _rushing into a centre_ in which the atmosphere has
become extremely condensed. According to this theory, a storm is a
mighty whirlwind.

     A most violent hurricane occurred in 1780, which destroyed Lord
     Rodney's fleet, and a vast number of merchant ships. It is said to
     have killed 9,000 persons in Martinique alone, and 6,000 in St.
     Lucia. The town of St. Pierre in Martinique was totally destroyed;
     and only fourteen houses in the town of Kingston, in St. Vincent,
     were left uninjured.

677. _Why do the most violent storms occur in and near the tropics?_

Because there the temperature is very high, and the cold currents
of air rushing towards the equator from the poles, causes great
_atmospheric disturbance_.

678. _What are whirlwinds?_

Whirlwinds are produced by violent and contrary currents meeting and
striking upon each other, producing _a circular motion_. They generally
occur after long calms, attended by much heat.

Whirlwinds occurring at sea, or over the surface of water, sometimes
put the water in motion, and as the wind rises upwards it lifts with it
a whirling mass of water, producing a _water spout_.

[Verse: "Out of the south cometh the whirlwind; and cold out of the
north."--JOB XXXVII.]

[Illustration: Fig. 19.--A WATER SPOUT.]

679. _Why does the chimney smoke when the fire is first lighted?_

Because the air in the chimney is of the same temperature as that in
the room, and therefore _will not ascend_.

680. _Why does the smoking (into the room) cease, after the fire has
been lighted a little while?_

Because the air in the chimney, being warmed by the fire beneath,
becomes lighter and ascends rapidly.

681. _Why does a long chimney create a greater draught than a short
one?_

Because the short chimney contains _less air_ than the long one; there
is, consequently, less difference of weight between the warm air of
the short chimney and the external air; it therefore has not so great
an _ascensive power._

[Verse: "And, lo, the smoke of the country went up as the smoke of a
furnace."--GEN. XIX.]

682. _Why does smoke issue in folds and curls?_

Because it is _pressed upon_ by the _cold air_ which always _rushes
towards a rarer atmosphere_. It thus illustrates the development of
_storms_.

683. _Why do some chimneys smoke when the doors and windows are closed?_

Because the draught of air is not sufficient to supply the wants of the
fire, and enable it to create an _upward current_.

684. _What is the best method of conveying air to fires?_

Tubes built in the walls, communicating with the outer air, and
terminating _underneath the grates_.

685. _Why is this the best method of ventilation?_

Because doors and windows may then be made air-tight, and _draughts
across rooms be prevented_.

686. _Why do chimneys that stand under elevated objects, such as hills,
trees, and high buildings, smoke?_

Because the wind, striking against the elevated object, _flies back_,
and a part of it _rushes downward_.

687. _Why do sooty chimneys smoke?_

Because the accumulation of the soot _diminishes the size of the
flue_, and lessens the ascensive power of the draught, by reducing the
quantity of _warm air_. It also obstructs the motion of the air, by the
_roughness of its surface_.

688. _Why do chimneys smoke in damp and gusty weather?_

Because the ascending air is _suddenly chilled_ by gusts of damp and
cold air, and driven down the chimney.

[Verse: "Remember that thou magnify his work, which men behold.
Every man may see it; man may behold it afar off."--JOB XXXVI.]

689. _Why does smoke ascend in a straight line in mild and fine
weather?_

Because the air is still, and being dry and warm it _does not chill the
smoke_, nor drive it out of its course.

690. _Why do the wings of wind-mills turn round?_

Because the wind, striking _at an angle_ upon the wings, forces them
aside; and as there are four wings all upon the same angle, and fixed
upon the same centre, the _oblique pressure_ of the wind causes the
centre to rotate.

     There is a world of _miniature phenomena_ which has never been
     fully recognised, in which we may see the mightier works of nature
     pleasingly and truthfully illustrated.

     When the wind blows into the corner of a street, and whirling
     around, catches straw, dust, and feathers in its arms, and then
     wheels away, flinging the troubled atoms in all directions,--it
     is a miniature of the mightier _whirlwind_, which wrecks ships,
     uproots trees, and levels houses with the earth.

     When a cloud of dust, on a hot summer's day, rises and flies
     along the thirsty road, making the passenger close his eyelids,
     and dusting the leaves of wayside vegetation,--it is a miniature
     of the terrible _simoom_, which blows from the desert sands,
     scattering death and devastation in its track.

     When steam issues from the tea-urn, and becomes condensed in
     minute drops upon the window-pane,--the miniature is of the
     _earth's heat_, evaporating the waters, and the cold air of night
     condensing the vapours into _dew_.

     When grass and corn bend before the wind, and are beaten down by
     its force; when the pond forgets its calm, and rises in troubled
     waves, casting the flotilla of natural boats that move upon its
     surface, in rude disorder upon its windward shore,--the little
     storm is but a miniature of those great _hurricanes_ which wrecked
     a fleet in the Black Sea, and levelled the encampments of a mighty
     army.

     When the snow that has gathered upon the house-top, warming
     beneath the smiles of the sun, slips from its bed, and drops in
     accumulated heaps from the roof,--it is a miniature of those
     terrible _avalanches_ which in the Pyrenees bury villages in their
     icy pall, and doom man and beast to death.

     When the rivulet hurries on its course, and meeting with
     obstructions, leaps over them in mimic wrath, overturning some
     little raft upon which, perchance, a weary fly has alighted,--it
     is a miniature of those _rapids_ on whose banks the hippopotamus
     and the alligator yet live; and where, though rarely, man may be
     seen directing his raft over the troubled current, amid the rush
     of _debris_ from forests unexplored.

     And when, in a basin of the rivulet, two opposing currents meet,
     and form a little vortex into which insect life and vegetable
     fragments coming within the sphere of its influence are drawn,--it
     is a miniature of the roaring _whirlpool_, or the wilder
     _maelstrom_ of the Norwegian seas.

     Nature rehearses all her parts in mild whispers; and for every
     picture that she paints, she places a first study upon the canvas.
     Man need not go into the heart of her terrors to understand their
     laws. Many an unknown Humboldt, sitting by the river's side,
     may rejoice in the "aspects of nature," and share the bliss of
     knowledge with the great philosopher.

[Verse: "Can any understand the spreadings of the clouds, or the
noise of his tabernacle?"--JOB XXXVI.]




CHAPTER XXXII.


691. _What is a barometer?_

A barometer is an instrument which _indicates the pressure of the
atmosphere_, and which takes its name from two Greek words signifying
_measurer of weight_.

692. _Why does a barometer indicate the pressure of the atmosphere?_

Because it consists of a tube containing _quicksilver_, closed at one
end and open at the other, so that the pressure of the air upon the
open end balances the weight of the column of mercury (quicksilver),
and when the pressure of the air upon the open surface of the mercury
increases or decreases, the mercury _rises or falls_ in response
thereto.

693. _Why is a barometer called also a "weather-glass"?_

Because changes in the weather are generally preceded by _alterations
in the atmospheric pressure_. But we cannot perceive those changes
as they gradually occur; the alteration in the height of the column
of mercury, therefore, enables us to know that atmospheric changes
are taking place, and, by observation, we are enabled to determine
certain rules by which _the state of the weather may be foretold_ with
considerable probability.

694. _Why are barometers constructed with circular dials, and an index
to denote changes?_

Because that is a convenient mechanical arrangement, by which the
alterations of the relative pressures of the air and the mercury are
_more clearly denoted than by an inspection of the mercury itself._

[Verse: "Fair weather cometh out of the north: with God is terrible
majesty."--JOB XXXVII.]

[Illustration: Fig. 20.--BAROMETER.]

[Illustration: Fig. 21.--TUBE OF BAROMETER, WHEEL, AND PULLEY.]

695. _Why does the hand of the weather dial change its position when
the column of mercury rises or falls?_

Because a weight, which _floats upon the open surface of the mercury_,
is attached to a string, having a nearly equal weight at the other
extremity; the string is laid over a revolving pivot to which the
hand is fixed, and _the friction of the string turns the hand, as the
mercury rises or falls_.

[Verse: "Thou visitest the earth, and waterest it: thou greatly
enrichest it with the river of God, which is full of water: thou
preparest them corn, when thou hast so provided for it."--PSALM LXV.]

696. _Why does tapping the face of the barometer sometimes cause the
hand to move?_

Because the weight on the surface of the mercury frequently _leans
against the sides of the tube_, and does not move freely. And, also,
the mercury clings to the sides of the tube by _capillary attraction_;
therefore, tapping on the face of the barometer _sets the weight free_,
and overcomes the attraction which _impedes the rise or fall of the
mercury_.

     Fig. 21 illustrates the mechanism at the back of the barometer. A
     is a glass tube; between A and E there exists a _vacuum_, caused
     by the weight of the mercury pressing downwards. This space
     being a vacuum, makes the barometrical column more sensitive, as
     there is no internal force to resist or modify the effects of
     the external pressure. E represents the height of the column of
     mercury; C the open end of the tube; F the weight resting on the
     surface of the mercury; P the pivot over which the string passes,
     and upon which the hand turns; W the weight which forms the pulley
     with the weight F.

697. _Which is the heavier, dry or vaporised air?_

Dry air is _heavier_ than air impregnated with vapours.

698. _Why is dry air heavier than moist air?_

Because of the _extreme tenuity of watery vapours_, the density of
which is _less than that of atmospheric air_.

699. _Why does the fall of the barometer denote the approach of rain?_

Because it shows that as the air _cannot support the full weight of the
column of mercury_, the atmosphere must be thin with watery vapours.

     The fall of the mercury in the long arm of the tube would cause
     the weight F to be pressed upwards. This would release the string
     to which the weight W is attached; it would, therefore, fall, and
     turn the hand down to Rain or Much Rain.

700. _Why does the rise of the barometer denote the approach of fine
weather?_

Because the external air becoming dense, and free from highly elastic
vapours, presses with increased force upon the mercury upon which the
weight F floats; that weight, therefore, sinks in the short tube as the
mercury rises in the long one, and in sinking turns the hand to Change,
Fair, &c.

[Verse: "He caused an east wind to blow in the heaven; and by his
power he brought in the south wind."--PSALM LXXVIII.]

701. _Why does the barometer enable us to calculate the height of
mountains?_

Because, as the barometer is carried up a mountain, _there is a less
depth of atmosphere above to press upon the mercury_; it therefore
falls, and by comparing various observations, it has been found
practicable to _calculate the height of mountains by the fall of the
mercury in a barometer_.

702. _To what extent of variation is the weight of the atmosphere
liable?_

It may vary as much as _a pound and a half to the square inch_ at the
level of the sea.

703. _When does the barometer stand highest?_

When there is a _duration of frost_, or when _north-easterly winds_
prevail.

704. _Why does the barometer stand highest at these times?_

Because the atmosphere is exceedingly _dry and dense_, and fully
balances the _weight of the column of mercury_.

705. _When does the barometer stand lowest?_

When _a thaw follows a long frost_; or when _south-west winds_ prevail.

706. _Why does the barometer stand lowest at those times?_

Because _much moisture exists in the air_, by which it is rendered less
dense and heavy.

707. _What effect has heat upon the barometer?_

It causes the mercury to fall, _by evaporating moisture into the air_.

708. _What effect has cold upon the barometer?_

It causes the mercury to rise, by _checking evaporation_, and
_increasing the density of the air_.

[Verse: "For so the Lord said unto me, I will take my rest, and I
will consider in my dwelling place like a clear heat upon herbs, and
like a cloud of dew in the heat of harvest."--ISAIAH XVIII.]

     In noting barometrical indications, more attention should be paid
     to the _tendency_ of the mercury at the time of the observation,
     than to the _actual state of the column_, whether it stands _high_
     or _low_. The following rules of barometric reading are given as
     generally accurate, but liable to exceptions:--

     _Fair weather_ indicated by the _rise_ of the mercury.

     _Foul_ weather by the _fall_ of the mercury.

     _Thunder_, indicated by the _fall_ of the mercury in _sultry
     weather_.

     _Cold_, indicated by the _rise_ of the mercury in spring, autumn,
     and winter.

     _Heat_, by the _fall_ of the mercury in summer and autumn.

     _Frost_, indicated by the _rise_ of the mercury in winter.

     _Thaw_, by the _fall_ of the mercury during a frost.

     _Continued bad weather_, when the _fall_ of the mercury has been
     _gradual_ through several fine days.

     _Continued fine weather_, when the _rise_ of the mercury has been
     _gradual_ through several foul days.

     _Bad weather of short duration_, when it sets in quickly.

     _Fine weather of short duration_, when it sets in quickly.

     _Changeable weather_, when an _extreme_ change has _suddenly_ set
     in.

     _Wind_, indicated by a rapid _rise_ or _fall unattended by a
     change of temperature_.

     The mercury _rising_, and the air becoming _cooler_, promises
     _fine weather_; but the mercury _rising_, and the air becoming
     _warmer_, the weather will _be changeable_.

     If the top of the column of mercury appears _convex_, or curved
     upwards, it is an additional proof that the mercury is _rising_.
     Expect _fine_ weather.

     If the top of the column is _concave_, or curved downwards, it is
     an additional proof that the mercury is _falling_. Expect _bad_
     weather.




CHAPTER XXXIII.


709. _What is the thermometer?_

The thermometer is an instrument in which _mercury_ is employed to
indicate _degrees of heat_. Its name is derived from two Greek words,
meaning _heat measurer_.

710. _Why does mercury indicate degrees of heat?_

Because it _expands_ readily with _heat_, and _contracts_ with _cold_;
and as it passes freely through small tubes, it is the most convenient
medium for indicating _changes of temperature_.

711. _Why are there Reaumur's Thermometers and Fahrenheit's
Thermometers?_

Because their inventors, after whom they are named, adopted a different
system of _notation_, or _thermometrical marks_; and as their
thermometers have been adopted by various countries and authors, it is
now difficult to dispense with either of them.

[Verse: "When ye see a cloud rise out of the west straightway ye
say, There cometh a shower; and so it is. And when ye see the south
wind blow, ye say there will be heat; and it cometh to pass."--LUKE
XIII.]

[Illustration: Fig. 22.--THE THERMOMETERS OF REAUMUR AND FAHRENHEIT
COMPARED.]

     We have combined the two (_see_ Fig. 22.) The diagram will, we
     have no doubt, prove exceedingly useful to scientific readers
     and experimentalists. There is also another system of notation,
     adopted by the French, called the _centigrade_, but it is not much
     referred to in Great Britain. In the centigrade thermometer 0 zero
     is the freezing point, and 100 the boiling point. Fahrenheit's
     scale is generally preferred. Reaumur's is mostly used in Germany.
     Of Fahrenheit's scale 32 is the freezing point, 55 is moderate
     heat, 76 summer heat in Great Britain, 98 is blood heat, and 212
     is the boiling point. Mr. Wedgwood has invented a thermometer for
     testing _high temperatures_, each degree of which answers to l30
     degrees of Fahrenheit. According to his scale cast iron melts at
     2,786 deg.; fine gold at 2,016 deg.; fine silver 1,873 deg.; brass
     melts at 1,869 deg.; red heat is visible by day at 980 deg.; lead
     melts 612 deg.; bismuth melts 476 deg.; tin melts 412 deg.; and
     there is a curious fact with regard to the three metals, lead,
     bismuth, and tin, that if they are mixed in the proportions of 5,
     8, and 3 parts respectively, the mixture (after previous fusion)
     will melt at a heat below that of boiling water.

712. _What is the difference between the thermometer and the barometer?_

In the thermometer the column of mercury is much smaller than in the
barometer, and is sealed from the air; while in the barometer the
column of mercury is open at one end to atmospheric influence.

713. _Why does the mercury in the thermometer, being sealed up,
indicate the external temperature?_

Because the heat passes through the glass, in which the mercury is
enclosed, and _expanding or contracting the metal within the bulb_,
causes the small column above it to _rise_ or _fall_.

[Verse: "Blessed is the people that know the joyful sound: they
shall walk, O Lord, in the light of thy countenance."--PSALM LXXXIX.]

714. _When does the thermometer vary most in its indication of natural
temperature?_

It varies more in the _winter_ than in the _summer_ season.

715. _Why does it vary more in the winter than in the summer?_

Because the temperature of our climate _differs more from the
temperature of the torrid zones in the winter_ than it does in the
_summer_, and the _inequalities of temperature_ cause frequent changes
in the degree of prevailing heat.

The same remarks (714, 715,) apply to the barometer.




CHAPTER XXXIV.


716. _What is sound?_

Sound is an _impression produced upon the ear_ by _vibrations_ of _the
air_.

717. _What causes the air to vibrate and produce sounds?_

The atoms of _elastic bodies_ being caused to _vibrate_ by the
application of some kind of force, _the vibrations of those atoms are
imparted to the air_, and sound is produced.

718. _How do we know that sounds are produced by the vibrations of the
air, induced by the vibrations of the atoms of bodies?_

If we take a tuning fork, and hold it to the ear, we hear _no sound_.
If we move it rapidly through the air, or if we blow upon it, it
produces _no sound_; but if we _strike it_, _a sound immediately
occurs_; the vibration of the fork may be seen, and felt by the hand
that holds it; and _as those vibrations cease_, the sound _dies away_.

719. _How do we know that without air there would be no sound?_

Because if a tuning fork were to be struck in a _vacuum_ (as under
the receiver of an air pump) _no sound_ would be heard, although the
_vibrations_ of the fork could be _distinctly seen_.

[Verse: "And even things without life giving sound, whether pipe or
harp, except they give a distinction in the sounds, how shall it be
known what is piped or harped."--CORINTH. XIV.]

720. _How are the vibrations of sonorous bodies imparted to the air?_

When a bell is struck, the force of the blow gives an instant agitation
to all its particles. The air around the bell is driven back by the
impulse of the force, and thus a _vibration of compression_ is imparted
to the air; but the air returns to the bell, by its own natural
elasticity, thus producing a _vibration of expansion_--when it is again
struck, and thus _successive vibrations_ of compression and expansion
are _transmitted through the air_.

721. _How rapidly are these vibrations transmitted through the air?_

They travel at a rate of rather more than _a quarter of a mile in a
second_, or _twelve miles and three-fourths in a minute_.

722. _Do all sounds travel at the same rate?_

All sounds, whether strong or weak, high or low, musical or discordant,
_travel with the same velocity_.

723. _Why are bells and glasses stopped from ringing by touching them
with the finger?_

Because the contact of the finger _stops the vibration_ of the atoms of
the metal and glass, which therefore _cease to impart vibrations to the
air_.

724. _Why does a cracked bell give discordant sounds?_

Because the _connection_ between the atoms of the bell being _broken,_
their vibrations are not uniform: some of the atoms vibrate _more
intensely_ than the others; the vibrations imparted to the air are
therefore _jarring_ and _discordant_.

725. _Why, when we see a gun fired at a distance, do we see the flash
and smoke, before we hear the report?_

Because _light,_ which enables us to _see_, travels at the velocity of
192,000 miles in a _second_; while _sound_, by which we _hear_, travels
only at the rate of a quarter of a mile in a _second_.

[Verse: "My heart maketh a noise in me: I cannot hold my peace,
because thou hast heard, O my soul, the sound of the trumpet, the alarm
of war."--JER. IV.]

726. _Why does the tread of soldiers, when marching in long ranks,
appear to be irregular?_

Because the sounds proceeding from _different distances_, reach our
ears in _varying periods of time_.

727. _What are the numbers of vibrations in a second that produce the
various musical sounds?_

C or Do, 480 vibrations in a second; B or Si, 450 vibrations; A or La,
400 vibrations; G or Sol, 360 vibrations; F or Fa, 320 vibrations; E or
Mi, 300 vibrations; D or Re, 270 vibrations; C or Do, 240 vibrations.
It is thus seen that the _more rapid_ the vibrations, the _higher_ the
note, and _vice versa_.

728. _Why does the length of a wire or string determine the sound that
it produces?_

Because the _shorter the string_ the _more rapid_ are its vibrations
when struck.

729. _Why does the tension of a wire or string affect its vibrations?_

Because when the string or wire is tight, a touch communicates
vibrations to _all its particles_; but when it is loose the vibrations
are _imperfectly communicated_.

730. _Why are some notes low and solemn, and others high and quick?_

Because the vibrations of musical strings vary from 32 vibrations in a
second, which produces a soft and deep bass, to 15,000 vibrations in a
second, which produces the sharpest treble note.

731. _Why can our voices be heard at a greater distance when we speak
through tubes?_

Because the vibrations are _confined to the air within the tube_, and
are not interfered with by _other vibrations_ or movements in the air;
the tube itself is also a _good conductor of sound_.

[Verse: "And I will cause the noise of thy songs to cease; and the
sound of thy harps shall no more be heard."--EZEKIEL XXVI.]

732. _Is air a good conductor of sound?_

Air is a _good conductor_, but water is a _better conductor than air_;
wood, metals, the earth, &c., are also _good conductors_.

733. _Why can we hear sounds at a greater distance on water than on
land?_

For various reasons: because the smooth surface of water is a good
conductor; because there are fewer noises, or counter vibrations, to
interfere with the transmission of sound; and because there are no
elevated objects to impede the progress of the vibrations.

734. _Why do sea-shells give a murmuring noise when held to the ear?_

Because what may be called _expended vibrations_ always exist in air
where various sounds are occurring. These _tremblings_ of the air are
received upon the thin covering of the shell, and thus being _collected
into a focus_, are _transmitted to the ear_.

735. _Why can people in the arctic regions converse when more than a
mile apart?_

Because there the air, being _cold and dense_, is a very good
conductor; and the _smooth surface of the ice_ also favours the
_transmission of sound_.

736. _Why do savages lay their heads upon the earth to hear the sounds
of wild beasts, &c.?_

Because the earth is a good conductor of sound. For this reason, also,
persons _working under ground in mines_ can hear each other digging at
considerable distances.

737. _Why can church clocks be heard striking much more clearly at some
times than at others?_

Because the density of dry air improves the _sound-conducting power_
of the atmosphere. The transmission of sounds is also assisted by the
direction of the winds.

738. _Why may the scratching of a pin at one extremity of a long pole
be heard by applying the ear to the opposite extremity?_

Because wood is a good conductor of sound, and its atoms are
_susceptible of considerable vibration_. It is, therefore, chosen in
numerous instances for the construction of _musical instruments_.

[Verse: "The morning is come unto thee, O thou that dwellest in
the land: the time is come, the day of trouble is near, and not the
sounding again of the mountains."--EZEKIEL VII.]

     Deaf persons have been known to derive pleasure from music by
     placing their hands upon the wood-work of musical instruments
     while being played upon.

739. _Why is the hearing of deaf persons assisted by ear-trumpets?_

Because ear-trumpets _collect the vibrations of the air_ into a focus,
and make the sounds produced thereby more intense.

740. _Why are sounding-hoards used to improve the hearing of
congregations?_

Because, being suspended over, and a little behind, the speaker, they
_collect the vibrations_ of the air, and _reflect_ them towards the
congregation.

741. _What are echoes?_

Echoes are sounds _reflected_ by the objects on which they strike.

742. _Why do some echoes occur immediately after a sound?_

Because the reflecting surface is _very near_; therefore the sound
returns immediately.

743. _Why do some echoes occur a considerable time after a sound?_

Because they are at a considerable distance, and the sound takes time
to travel to it, and an equal time to return.

744. _Why do some echoes change the tone and quality of sound?_

Because the reflecting surface, having vibratory qualities of its own,
_mingles its own vibrations with that of the sound_.

745. _Why are there sometimes several echoes to one sound?_

Because there are various _reflecting surfaces_, at different
distances, each of which returns an echo.

[Verse: "And God said, Let the waters under the heaven be gathered
together onto one place, and let the dry land appear: and it was
so."--GEN. I.]

746. _Are sounds reflected only by distant objects?_

Sounds are doubtless reflected by _walls and ceilings_ around us. But
we do not perceive the echoes, because they are so near that they occur
at the same moment with the sound. In lofty buildings, however, there
is frequently a _double sound_, making the utterance of a speaker
indistinct. This arises from the echo following very closely upon the
sound.

747. _Why, when we are walking under an arch-way or a tunnel, do our
voices appear louder?_

Because the sounds of our voices are _immediately reflected_. And
as a _gas reflector increases the intensity of light_, so _a sound
reflector_ will _increase the apparent strength of our voices_.

     There are many places where remarkable echoes occur. On the
     banks of the Rhine, at Lurley, if the weather be favourable, the
     report of a rifle, or the sound of a trumpet, will be repeated at
     different periods, and with various degrees of strength, from crag
     to crag, on opposite sides of the river alternately. A similar
     effect is heard in the neighbourhood of some of the Lochs in
     Scotland. There is a place at Woodstock, in Gloucestershire, which
     is said to echo a sound fifty times. Near Rosneath, a few miles
     from Glasgow, there is a spot where, if a person plays a bar of
     music upon a bugle, the notes will be repeated by an echo, but a
     third lower; after a short pause, another echo is heard, again in
     a lower tone; then follows another pause, and a third repetition
     follows in a still lower key. The effect is very enchanting. The
     whispering galleries of St. Paul's, of the cathedral church of
     Gloucester, and of the Observatory of Paris, owe their curious
     effects to those laws of the reflection of sound, by which echoes
     are produced; but in these cases the effect is assisted by the
     elliptical form of the edifice, each person being in the focus of
     an ellipse.




CHAPTER XXXV.


748. _What is water?_

Water is a fluid composed of _two_ volumes of _hydrogen_ to _one_
of _oxygen_, or _eight_ parts by weight of _oxygen_ to _one_ of
_hydrogen_. It is nearly colourless and transparent.

749. _Why, if a saucer of water be exposed to the air, will it
gradually disappear?_

Because water is highly expansive, and _rises in thin vapour_, when in
contact with warm and dry air.

[Verse: "Behold there ariseth a little cloud from the sea, of the
bigness of a man's hand. And it came to pass in the meantime, that the
heaven was black with clouds and wind, and there was a great rain."--1
KINGS XVIII.]

750. _Why does steam issue from the spout of a kettle?_

Because the heat of the fire passes into the water, and _drives_ its
atoms apart, making those of them that rise quickly to the surface
_lighter than the air_, upon which they consequently rise.

751. _Why does water become solid when it freezes?_

Because the _latent heat of the water_ passes away from between its
atoms into the air; the atoms, therefore, draw closer together.

752. _Why, if the atoms of water draw closer together when freezing,
does ice expand, and occupy greater space than water?_

Because, _when the atoms of water are congealing_, they do not form a
_compact mass_, but arrange themselves _in groups of crystal points_,
which occupy greater space. Water _contracts_ when freezing until it
sinks to 40 deg., and then it _expands_ as ice is formed.

     32 deg. is said to be the _freezing_ point, but it should be
     called the _frozen_ point.

753. _Why does water boil?_

Because heat, _entering into the lower portions_ of the water,
_expands_ it; the heated portions are then _specifically lighter_ than
those that are cooler; the hot water therefore _rises upward, and
forces the cooler water down_.

754. _What proportion of the earth's surface is covered with water?_

There are about one hundred and forty seven millions of square miles of
_water_, to forty-nine and a half millions of square miles of _land_.

755. _What is the amount of water pressure?_

The pressure of the sea, at the depth of 1,100 yards, is equal to
15,000 lbs. _to the square inch_.

[Verse: "But the land, whither ye go to possess it, is a land of
hills and valleys, and drinketh water of the rain of heaven."--DEUT.
XI.]

756. _What element is the most abundant in nature?_

_Oxygen_, which forms so large a part of _water_. Of animal substances,
_oxygen_ forms _three-fourths_; of _vegetable substances_ it forms
_four-fifths_; of _mineral substances_ it forms _one-half_; it forms
_eight-ninths_ of the _waters_ and _one-fifth_ of the _atmosphere_; and
aggregating the whole creation, from _one-half to two-thirds_ consists
of _oxygen_.

757. _In what ways does man use oxygen?_

Man _eats_, _drinks_, _breathes_, and _burns_ it, in various
proportions and combinations. It is estimated that _the human race_
consume in those various ways 1,000,000,000 lbs. daily; that the _lower
animals_ consume double that amount; and that, in the varied works of
nature, no less than 8,000,000,000 lbs. of _oxygen_ are used _daily_.

758. _Why does water dissolve various substances?_

Because the _atoms of water_ are very minute; they therefore _permeate
the pores_, or spaces, between the atoms of those bodies, and
_overcoming their attraction for each other_, cause them to separate.

759. _Why does hot water dissolve substances more readily than cold?_

Because the _heat assists to repel the particles_ of the substance
undergoing solution, and _gives the water a freer passage_ between the
atoms.

760. _Why is pump water sometimes hard?_

Because, in passing through the earth, it has become impregnated with
mineral matters, usually the _sulphate_ and _carbonate of lime_.

761. _Why is rain water soft?_

Because it is derived from vapours which, in ascending to the clouds,
_could not bear up the mineral waters with them_. It therefore became
purified or distilled.

762. _Why do kettles become encrusted with stony deposits?_

Because that portion of the water which is driven off in steam _leaves
the mineral matters behind_; they therefore form a crust around the
sides of the kettle.

[Verse: "He gathereth the waters of the sea together as an heap; he
layeth up the depth in storehouses."--PSALM XXXIII.]

     It is said that if a child's marble be placed in a kettle, it will
     attract the earthy particles, and prevent the encrusting of the
     sides of the vessel.

763. _Why is it difficult to wash in hard water?_

Because the soap unites with the mineral matters in the water, and
being _neutralised_ thereby, cannot _dissolve the dirt_ which we desire
to cleanse away.

764. _Why is the sea salt?_

Because salt is a mineral which prevails largely in the earth, and
which, _being very soluble in water_, is taken up by the ocean.

Lakes and rivers, also, even those that are considered fresh, hold in
solution _some degree of saline matters_, which they contribute to the
ocean.

As, in the evaporations from the sea, the salt remains in it, while the
vapours fall as rain, and again wash the earth and carry some of its
mineral properties to the ocean, the _greater saltness of the sea_, as
compared with rivers, is accounted for.

By some persons the opinion is entertained that the sea has been
_gradually getting salter_ ever since the creation of the world. This,
they say, arises from the evaporation of water free from salt, and the
returns of the water to the sea, taking with it salt from the land.

765. _What is the estimated amount of salt in the sea?_

The amount of common salt in the various oceans is estimated at
3,051,342 _cubic geographical miles_, or about five times more than the
mass of the mountains of the Alps.

766. _What is the depth of the sea?_

The extreme depth has not, probably, been ascertained. But Sir James
Ross took soundings about 900 miles west of St. Helena, whence he
found the sea to be nearly _six miles in depth_. Now, if we take the
height of the highest mountain to be five miles, the distance from that
extreme rise of the earth, to the known depth of the sea, will be no
less than _eleven miles_.

767. _Why are the waters of some springs impregnated with mineral
matters?_

Because the water passes through beds of soda, lime, magnesia, carbonic
acid, oxides of iron, sulphate of iron, &c., &c., and _takes up in
some slight degree the particles of those minerals_, according to the
proportions in which they abound.

[Verse: "Who hath measured the waters in the hollow of his hand, and
meted out heaven with the span, and comprehended the dust of the earth
in a measure and weighed the mountains in scales, and the hills in a
balance?"--ISAIAH XL.]

768. _Why does iron rust rapidly when wetted?_

Because the water contains a large proportion of oxygen, some of which
combines with the iron and forms _an oxide of iron_, which is _rust_.

769. _Why does stagnant water become putrid?_

Because the _large amount of oxygen_ which it contains accelerates the
decomposition of dead _animal and vegetable substances_ that accumulate
in it.

770. _Is there danger in drinking water on account of the living
animalcules which it contains?_

No danger arises from the _living creatures_ in water; but
_putrefactive_ matters may produce serious diseases.

771. _What is the best method of guarding against impurities?_

By obtaining water from the purest sources, and by filtering it before
drinking, by which nearly all extraneous matters would be _separated
from it_.




CHAPTER XXXVI.


772. _What is attraction?_

Attraction is the tendency of bodies to _draw near to each other_.
It is called _attraction_, from two Latin words signifying _drawing
towards_.

773. _How many kinds of attraction are there?_

There are five principal kinds of _attraction_:--

  1. The attraction of _gravitation_.
  2. The attraction of _cohesion_.
  3. The attraction of _chemical affinity_.
  4. The attraction of _electricity_.
  5. And _capillary attraction_.

[Verse: "Behold, the nations are as a drop of a bucket, and are
counted as the small dust of the balance: behold, he taketh up the
isles as a very little thing."--ISAIAH XL.]

774. _Why do all bodies heavier than the air fall to the earth?_

Because they are influenced by the _attraction of gravitation_, by
which all bodies are drawn towards _the centre of the earth_.

775. _Why do bodies lighter than the air ascend?_

Because the air, being a denser body, _obeys the law of attraction_,
and in doing so _displaces lighter bodies_ that interfere with its
gravitation.

776. _Why do fragments of tea, and bubbles floating upon the surface of
tea, draw towards each other, and attach themselves to the sides of the
cup?_

Because they are influenced by the _attraction of cohesion_.

     _Cohesion._--The act of sticking together.

777. _Why will a drop of water upon the blade of a knife leave a dark
spot?_

Because the _iron of the knife attracts the oxygen of the water_, by
_chemical affinity_; and the two substances form a thin coating of
_oxide of iron_.

     _Affinity._--Attraction between dissimilar particles through which
     they form new compounds.

778. _Why do clouds sometimes move towards each other from opposite
directions? and_

779. _Why do light particles of matter attach themselves to sealing
wax, excited by friction?_

Because they are moved by the _attraction of electricity_.

780. _Why will a towel, the corner of which is dipped in water, become
wet far above the water?_

Because the water is conveyed up through the towel, by _capillary
attraction_. The atoms of the water are attracted by the _threads of
the towel_, and drawn up into the _small spaces between the threads_.

     _Capillary._--Resembling a hair, small in diameter.

[Verse: "He stretcheth out the north over the empty place, and
hangeth the earth upon nothing."--JOB XXVI.]

781. _Why do small bodies floating upon water move towards larger ones?_

Because the attractive power of a _large body_ is greater than that of
_a small one_. As each atom of matter has inherent power of attraction,
it follows that a _large aggregation of particles_ must attract in
proportion to the number of those particles.

782. _Why do clouds gather around mountain tops?_

Because they are _attracted by the mountains_.

783. _Why would a piece of lead tied to a string, and let down from a
church steeple, incline a little from the perpendicular towards the
church?_

Because the _masses of stone_ of which the church is built would
_attract the lead_.

784. _How can man weigh the earth?_

By observing what is called the _deflection_ of small bodies _when
brought within given distances of larger bodies_, the degree of
attraction _exercised by the large body upon the smaller one_ becomes
known. This attraction of the _large body_ exercised over the _smaller
body_ is an opposing influence, _acting against the earth's attraction
of the small body_, which is drawn out of its course: it constitutes a
_natural balance between the influence of the earth and another body,
acting in opposition to it_. Founded upon these, and some other data,
man can weigh the earth, and give a morally certain result!

     _Deflection_.--The act of turning aside.

785. _How can man weigh the planets?_

The planets exercise as certain an influence upon each other _as do
two pieces of wood floating upon a basin of water_. As the planetary
bodies fly through their prescribed orbits, _and approach nearer to, or
travel further from, each other_, they are observed to _deviate_ from
that course which they must have pursued _but for the increase or the
decrease of some influence of attraction_. By making observations _at
various times_, and by comparing _a number of results_, it is possible
_to weigh any planetary body, however vast, or however distant_.

[Verse: "Is not God in the height of the heaven? and behold the
height of the stars, how high they are?"--JOB XII.]

786. _How can man measure the distances of the planets?_

By making observations at _different seasons of the year_, when the
earth is in _opposite positions in her orbit_; and by recording, by
_instruments constructed with the greatest nicety_, the _angle of
sight_, at which the planetary body is viewed; by noticing, also, _the
various eclipses_, and estimating _how long the first light after an
eclipse has ceased_ reaches the earth, it is possible to estimate the
_distances_ of heavenly bodies, _no matter how far in the depths of the
universe those orbs may be_.

787. _What are the opinions founded upon estimates respecting the
magnitude of the sun?_

The _diameter_ of the _sun_ is 770,800 geographical miles, or 112 times
greater than the diameter of the earth; its _volume_ is 1,407,124
times that of the earth, and 600 times greater than _all the planets
together_; its _mass_ is 359,551 times greater than the earth; and 738
times greater than that of _all the planets_. A _single spot_ seen upon
its surface has been estimated to extend over 77,000 miles in diameter,
and a _cluster of spots_ have been estimated to include an area of
3,780,000 miles.

788. _What is the weight of the earth?_

The earth has a _circumference_ of 25,000 miles, and is estimated to
_weigh_ 1,256,195,670,000,000,000,000,000 tons.

789. _What is the specific gravity of a body?_

It is its weight estimated _relatively to the weights of other bodies_.

790. _What determines the force with which bodies fall to the earth?_

Generally speaking, their _specific gravity_, which is proportionate to
the density, or _compactness of the atoms_ of which they are composed.

791. _Why does a feather fall to the earth more gradually than a
shilling?_

Because the _specific gravity_ of the feather and of the shilling is
_relative to that of the air_, the medium through which the feather and
the shilling pass. If there were _no air_, a shilling and a feather
dropped at the same time from a height of forty miles, _would reach the
earth at the same moment_.




CHAPTER XXXVII.


[Verse: "Where wast thou when I laid the foundations of the earth?
declare, if thou hast understanding."]

792. _What is repulsion?_

Repulsion is that property in matter by which it _repels_ or _recedes
from_, those bodies for which it has _no attraction or affinity_.

793. _Why does dew form into round drops upon the leaves of plants?_

Because it _repels the air_, and the _substances of the leaves_ upon
which it rests. Because, also, its own particles _cohere_.

794. _Why do drops of water roll over dusty surfaces?_

Because they _repel_ the particles of dust; and also because their own
particles have _a stronger attraction for each other_ than for the
particles of dust.

795. _Why does a needle float when carefully laid upon the surface of
water?_

Because the needle and the water _mutually repel each other_.

796. _Why does water, when dropped upon hot iron, move about in
agitated globules?_

Because the _caloric_ repels the particles of the water.

797. _Why does oil float upon the surface of water?_

Because, besides being specially lighter than water, the particles of
the oil and the water _mutually repel each other_.

798. _What is carbonic acid?_

Carbonic acid is a mixture of _carbon_ and _oxygen_, in the proportion
of 3 lbs. of carbon to 8 lbs. of oxygen.

[Verse: "Who hath laid the measures thereof, if thou knowest? or who
hath stretched the line upon it?"]

799. _Where does carbonic acid chiefly exist?_

It exists in various natural bodies in which carbon and oxygen are
combined; it is evolved by the decomposition of numerous bodies called
carbonates, in which carbon is united with a particular base, such as
the carbonate of lime, the carbonate of iron, the carbonate of copper,
&c. It is also evolved by the processes of _fermentation_, by the
_breathing of animals_, the _combustion of fuel_, and the _functions of
plants_. Carbonic acid also _exists in various waters_.

Carbonic acid is _found most largely in solid combinations with other
bodies_: it forms 44-100ths of all limestones and marbles, and it
exists in smaller quantity, combined with other earths, and with
metallic oxides.

800. _What are the states in which pure carbonic acid exists?_

Pure carbonic acid may exist in the _solid_, the _liquid_, or the
_æriform_ state. In the _solid state_ it is produced only by artificial
means, and it is then a white crystallised body, in appearance _like
snow_; in the _liquid state_ it is a _heavy colourless fluid_; in the
_æriform state_ it is a _pungent_, _heavy_, _colourless gas_, and is
known as _carbonic acid gas_.

801. _Why does bottled porter produce large volumes of froth, much more
than the bottle could contain?_

Because, by the fermentive process, _carbonic acid_ has been developed
in the porter, and is held in _liquid solution_; but it always has a
_strong tendency to escape_, and directly the pressure is removed, it
_evolves into gas_, by which it occupies much greater space, and forces
the porter in millions of small bubbles out of the bottle.

802. _Why does soda-water effervesce?_

Because _carbonic acid gas_ is forced into the water _by pressure_.
Pressure _alters the gas into a liquid_, and directly the pressure
ceases, the liquid again _evolves into gas_.

803. _Why does spring water taste fresh and invigorating?_

Because it contains _carbonic acid_.

[Verse: "Whereupon are the foundations thereof fastened? or who laid
the cornerstone thereof."--JOB XXXVIII.]

804. _Why does boiled water taste flat and insipid?_

Because the _carbonic acid_ has been _driven off_ by boiling.

805. _Why does beer which has been standing in a glass taste flat?_

Because its _carbonic acid_ has escaped as _carbonic acid gas_.

806. _Why, when we look into a glass of champagne, do we see bubbles
spontaneously appear at the bottom, and then rise to the top?_

Because, in the places where the bubbles are formed, the _liquid
carbonic acid_ is evolving into _carbonic acid gas_.

807. _Why do the bubbles arise from two or three points in columns,
rapidly succeeding each other?_

Because, when the formation of gas once begins, and bubbles ascend,
there is _less pressure_ in the line of the _column of bubbles_; the
carbonic acid, therefore, draws towards those points as the _easiest
channel of escape_.

     These explanations equally apply to the "working" of beer, by
     which yeast is produced; to the effervescence of various waters,
     acidulated drinks, ginger beer, &c., and also to the "sponging" of
     bread, &c.

808. _Why does gunpowder explode?_

Gunpowder is made of a very intimate _mechanical mixture_ of _nitrate
of potash_, _charcoal_, and _sulphur_. When these substances are heated
to a certain degree, the nitrate of potash is decomposed, and its
_oxygen_ combines with the _charcoal_ and _sulphur_, instantaneously
forming _large volumes of carbonic acid gas_ and _nitrogen_, which,
seeking an escape, produce an explosion.

809. _Why does charcoal act as a powerful disinfectant?_

Because the _carbon_ readily absorbs, and combines with _various
gases_, neutralising their _offensive odours_, and destroying their
_unhealthy properties_.

     Let us now pause for a few moments to consider the importance of
     those two great divisions of nature, Air and Water, and to reflect
     upon the wisdom of some of those laws which are connected with
     the phenomena thereof, and which have not yet been sufficiently
     explained.

[Verse: "Thus saith the Lord, Let not the wise man glory in his
wisdom, neither let the mighty man glory in his might, let not the rich
man glory in his riches."--JEREMIAH IX.]

     We have seen that the air is a thin elastic body surrounding the
     globe; that it consists of certain gases essential to the life of
     animals, and to the growth of plants; and that it takes part in
     most of those chemical changes, which mark the transformations
     of the inorganic creation. Whether it be the burning of a piece
     of wood, the evaporation of a drop of water, the breathing of an
     animal, the respiration of a plant, or the fermentation of bodies,
     the air in almost every instance gives or receives--and in most of
     the operations in which it engages, it does both.

     But there is one point of view, which we must add to those which
     have already been considered: the order of nature consists of
     generation, life, and death. Every beat of the watch signals the
     birth of millions of living things, and the same beat proclaims
     that as many living organisms have yielded up their vital spark,
     and that forthwith the elements of which they are composed must be
     dissolved, and restored to the great laboratory of nature.

     The air is the vast receptacle of those organic matters which are
     undergoing dissolution. The body of the shipwrecked mariner, cast
     upon the shore of a desolate island, blackens in the sun, and the
     full round form gradually dwindles to skin and bone, until at last
     the few atoms that remain crumble into dust, and are scattered
     to the wind. The same process occurs, with some modifications,
     whether bodies are buried in the earth, or dissolve upon its
     surface. The leaves of forests fall and accumulate in heaps,
     where they ferment and dissolve, leaving only their more earthy
     particles behind.

     The amount of matter which day by day passes from the state
     of the living to that of the dead, must be enormous; but from
     the difficulties of acquiring data, beyond the possibility of
     calculation. Such statistics as we have, however, enable us to
     form conclusions as to the mighty agencies in which the air
     is constantly engaged. There are on the earth 1,000,000,000
     inhabitants of whom nearly 35,000,000 die every year, 91,824 every
     day, 3,730 every hour, and 60 every minute. But _even the living
     die daily_, and undergo an invisible change of substance, as we
     shall hereafter explain.

     The bodies of those many millions are dissolved in the air, in
     vapours and gases which, before the dissolution of each corporeal
     organism is complete, begin to live again in the various forms of
     vegetable and animal life.

     Of the number of animals living and dying upon the face of the
     earth, we can form no adequate estimate. Of mammals there are
     about 2,000 ascertained species; of birds 8,000 species; of
     reptiles 2,000 species; of fishes some 8,000 or 10,000 species;
     of molluscs some 15,000 species; of shell fish 8,000 species; of
     insects 70,000 species. And, including others not specified here,
     the total number of _species_ of animals probably amounts to no
     less than 250,000,--each species consisting of _many millions_ of
     living creatures.

     In the area of London alone, no less than 200,000 tons of fuel
     are annually cast into the air in the form of smoke. And if we
     take into account the vast operations of nature in evaporation,
     fermentation, and putrefactive decomposition, we may be enabled
     to form a conception of the mighty part which that _thin air_, of
     which we think so little, plays in the grand alchemy of nature.

[Verse: "I will praise thee; for I am fearfully and wonderfully
made; marvellous are thy works; and that my soul knoweth right
well."--PSALM CXXXIX.]

     In addition, also, to the facts already communicated, respecting
     the sound-bearing and light-refracting properties of air, it
     must be remarked, that but for the atmosphere, and the general
     refraction of light by its particles--each atom as it were
     catching a fairy taper, and dancing with it before our view--the
     condition of vision would be widely opposite to that which exists,
     and totally unsuited to our wants. The various objects upon
     which the illuminating rays of the sun fell, would be lighted up
     with an intense glare, but all around would be darkness, just as
     when a single ray of light is passed into a dark chamber, and
     directed upon a solitary object. The air, without becoming itself
     visible, _diffuses luminous rays_, in modified intensity, in every
     direction. If the air reflected so much light as to render _itself
     visible_, it would appear like the glittering surface of the water
     reflecting the solar rays, and we should then be unable to see the
     various objects which surround us.

     Of the importance of Water in the scheme of creation, man
     generally entertains an imperfect conception. It is simply
     supposed to afford moisture to plants, drink to animals, and to
     promote salubrity by its cleansing properties. Let us, however,
     contemplate man as he stands before us, noble in form, erect
     in position, full of strength, joy, ambition. How much of that
     noble form is composed of water? Suppose that it could all be
     instantaneously withdrawn--not the oxygen and the hydrogen, which
     might combine to form water--but the fluid that exists in his
     body as _water_, unchanged--except by mechanical admixture with
     the secretions of the body--Why then that beautiful temple would
     collapse and become a mere shred, so thin, that it would seem but
     a shadow of the body as it existed before, and the beholder might
     doubt whether life ever inhabited a frame whose structure was so
     frail. It is said that _three-fourths_ by weight of the human body
     consist of _water_. Thus, if man weighs 120lbs., 90lbs. consist of
     water, and this subtracted, only 30lbs. of solid matter remain.
     This statement is rather under than over the fact.

     The assertion is startling, but so true that it can be verified
     by simple experiment. A piece of lean flesh--say of beef--cut an
     inch thick, and placed in a slow oven, and allowed to remain until
     all its water was driven off in vapour, would become as thin as a
     wafer, and as light as a cork. With a more scientific arrangement,
     it would be possible to collect the water, and the weights of the
     condensed vapour, and of the solid residue, would together make
     up the weight of the beef: if the piece weighed sixteen ounces,
     the weight of the water would be about 14 ounces, and the _solid
     matter_ about _two ounces_.

     Water holds a similar proportion in the bodies of all animals,
     and of vegetables. It is evident, therefore, that it occupies a
     more important place in the scale of creation than is generally
     accorded to it by the unobservant mind. We are indebted to it for
     those atmospheric changes which constitute the peculiar feature
     of our varying climate. Rising in invisible vapours, it builds
     palaces of glory in the skies, and often presents to the view of
     man the imagery of heaven. Persons who have ascended above the
     altitude of the clouds, have described the scene upon looking down
     towards them as the most celestial that the mind can conceive.
     Fields of fleecy radiance, majestically rolling like a sea of
     gold, occupied the whole range of vision, and seemed to embellish
     an eternity of space. Those golden clouds that at one time are
     decked in the richest splendour, and occupy the upper chambers
     of the Court of Nature, become grave councillors when the earth
     grows thirsty, and the plant droops with languor. They roll
     their heavy brows together, as in consultation upon some grave
     necessity: down come the refreshing showers, the mighty tongue
     of thunder rocks the air, the earth is drenched, and becomes
     fresh with the salubrity of her toilette; obnoxious substances,
     with their offensive exhalations, are swept away: living things
     rejoice, and beautiful flowers throw their incense in thanksgiving
     into the air; the broad blue heavens for a time look down and
     smile upon the blessed work; and then the clouds again gather
     in a golden train, and one by one fill the high arches of the
     atmosphere, until the earth once more grows thirsty, and the
     flower supplicates for drink.

[Verse: "How mighty are his wonders! his kingdom is an everlasting
kingdom, and his dominion is from generation to generation."--DANIEL
IV.]

     With reference to Light, its wonders, and the curious but
     imperfect theories respecting it, we have little to add, except
     with regard to its physiological action upon the eyes of man
     and of animals, which will be given in another place. But of
     its sister, Darkness--for it would not do now to call darkness
     the antagonist of light, since it will be seen that they work
     harmoniously for good--we have to say, that recent discoveries
     indicate that darkness is as necessary to the health of nature
     as light. Not only is it necessary to compose man and animals
     to sleep, to give rest to the over-wrought nerves of the
     industrious--but light is the quickening power of vegetation,
     and although plants grow by night, they grow, as man does, when
     stretched upon his bed--but some of their functions, which
     are actively excited in the presence of light, are at rest in
     darkness. Nor is this all: there is not an atom upon the face
     of the earth which is not affected by the rays of the sun,
     their light, their heat, their actinism. Colours change: some
     are bleached, others are darkened. All bodies are expanded. The
     hardest rock sustains _an effect_ from the sun's rays; and an
     unceasing sun, shining upon the hardest granite, would in time
     produce such a disturbance of its atomic condition, that adamant
     would crumble away to dust.

     The going down of the sun, therefore, marks the period when not
     only does the bird fly to her resting-place, and man turn to his
     couch; but when _every atom of a vast hemisphere_ subsides into a
     state of quietude, and when homogeneous particles of matter return
     to their mutual rest.

     In a few succeeding lessons, we intend to point out some of the
     scientific truths that are _illustrated in the use of toys_. We
     think we shall be able to show to our young readers, that even the
     hours of play may be made the periods of delightful instruction;
     and that there is _no_ "reason why" the acquirement of knowledge
     should not sweetly accord with the occasional pursuit of those
     pastimes by which health of body and vigour of mind are induced.

     But before we commence the discharge of that pleasant duty, let
     us say a few words respecting Carbon, that important agent in the
     world's history. It is, doubtless, perplexing to the minds of many
     persons, to understand how the _diamond_ can be _pure carbon_; how
     _charcoal_ can be _carbon_ a _little less pure_ than the diamond;
     and how _coal_ and _sugar_ can also be carbon, _less pure_ than
     the charcoal. The statement that in the diamond carbon exists in
     a different atomic condition, is almost as instructive to the
     inquiring mind, as to say, "It is so, _because it is_."

     Diamonds are expensive things, and so difficult to experiment
     upon, even if they were not expensive, that the doors of inquiry
     seem locked. To turn diamonds into charcoal, or into carbonic
     acid gas, is a very costly formula of experiment. Charcoal fires,
     thus sustained, would soon burn a man out of his house; and soda
     water, impregnated with carbonic acid gas, produced from diamonds,
     would be a very expensive beverage. If we could only turn charcoal
     into diamonds, and carbonic acid gas into brilliants, that would
     be quite another affair. A new Eldorado would be discovered,
     and there would be so many experimenters that, when they all
     succeeded, they would find that diamonds had lost their value.
     However, as a fact for the encouragement of those who would like
     to be early in the race, we may state that the atoms of charcoal
     which are repulsed from the charcoal points, during the electric
     agitation which produces the electric light, acquire a hardness
     and a sharpness almost equal to that of the diamond--only there
     is still the awkward obstacle in the way, that _they happen to be
     black_.

[Verse: "He delivereth and rescueth, and he worketh signs and
wonders in heaven and in earth."--DANIEL VII.]

     We must see, therefore, whether there is anything in nature that
     we can experiment upon, theoretically or practically, to give us
     a clearer conception of this difficult matter. There is a large
     _dew-drop_ resting upon a luxuriant cabbage leaf--one of those
     great leaves that have flourished in defiance of the snail, and
     now spreads out like the gigantic frond of the _Victoria Regina_.
     That dew-drop is one of the beautiful diamonds which Nature
     sprinkles about on cloudless nights, as if to show the stars,
     in answer to their twinkling, that we have something that will
     glisten and twinkle too.

     The dew-drop is a very good imitation of a diamond, and to the
     lover of God's works, quite as precious as the stone set in gold.
     It does not consist of carbon--it probably may have a mite of
     carbonic acid in its embrace--but that is not necessary to our
     purpose: all we want to know is, _the different atomic conditions_
     of which bodies are susceptible, and the very dissimilar
     appearances they exhibit under the variations of atomic states. It
     doesn't glisten so much as the diamond, _because it is round_--if
     we could cut it into a number of _facets_, it would refract light
     almost as perfectly as the diamond. It is not _solid_--but we
     can freeze it, and we shall at once exhibit two different atomic
     conditions, that will represent nearly enough the diamond, and
     the liquid carbonic acid. Then, if we evaporate the dew-drop, we
     shall produce a volume of vapour nearly _two thousand times as
     large as the dew-drop_. The steam will be white; but we have only
     to imagine it black, and then we get an analogy of the differences
     of the atomic conditions that prevail in _the diamond_, _carbonic
     acid_, and _charcoal_, _tinder_, _lamp-black_, or any light form
     of carbon. Of course we have been illustrating _atomic conditions
     only_, and not chemical composition.

     There are a few other facts connected with carbon that merit
     consideration. Carbonic acid gas, _entering the lungs_, is a
     _deadly poison_; but _entering the stomach_, which lies close
     under the lungs, and is over-lapped by them, it is a _refreshing
     beverage_. Although charcoal, when burnt, gives off the most
     poisonous gas, it seems to be very jealous of other gaseous
     poisons; for if it be powdered, and set about in pans where there
     is a poisonous atmosphere, it will seize hold of poisonous gases,
     and, by absorbing, imprison them. Even in a drop of toast and
     water, the charred bread seizes hold of whatever impurities exist
     in the water; and water passed through beds of charcoal, becomes
     filtered, and made beautifully pure, being compelled to give up
     to the charcoal whatever is obnoxious. If a piece of meat that
     has already commenced putrifying, be sprinkled with charcoal, it
     will not only object to the meat putrifying any further, but it
     will _sweeten that which has already undergone putrefaction_.
     Although, in the form of gas, it will poison the blood, and cause
     speedy stupefaction and death; if it be powdered, and stitched
     into a piece of silk, and worn before the mouth as a respirator,
     it will say to all poisonous gases that come to the mouth with the
     air, "I have taken this post to defend the lungs, and I arrest
     you, on a charge of murderous intention." Such are the various
     facts connected with carbon; and they forcibly indicate that those
     who understand Nature's works, are likely to receive her best
     protection.

[Verse: "The father of the righteous shall greatly rejoice; and he
that begetteth a wise child shall have joy of him."--PROVERBS XXIII.]




CHAPTER XXXVIII.


810. _Why does a humming-top make a humming noise?_

Because the hollow wood of the top vibrates, and the edges of the hole
in its sides _strike against the air as it spins_; the air is thereby
set in vibration.

811. _Why does a peg-top hum less than a humming-top?_

Because, _being a solid body of wood_, and having no _hole in its
sides_, its particles are _not so easily thrown into vibration_;
consequently it does not so readily impart vibrations to the air.

812. _Why does a peg-top sometimes hum, and at other times not?_

Because, if it is spun with _great force_, and its peg is _struck
sharply_ against the pavement, _the wood is set in vibration_, and
the surface of the top, repelling the air by its rapid motion, causes
_vibratory waves_. But if it be spun with insufficient force, _the wood
is not set in vibration_.

[Illustration: Fig. 23.--HUMMING-TOP BEFORE SPINNING.]

[Illustration: Fig. 24.--HUMMING-TOP SPINNING.]

813. _Why do we see the figures painted upon the humming-top, before it
spins, but not while it is spinning?_

Because the rapid whirling of the top brings the images of its
different parts so quickly in succession upon _the retina of the eye_,
that they _deface each other_, and _impart an impression of coloured
rings, instead of definite objects_.

[Verse: "Train up a child in the way he should go; and when he is
old, he will not depart from it."--PROVERBS XXII.]

814. _Why does a top stand erect when it spins, but fall when it stops?_

Because the top is under the influence of, and is balanced between
_opposing forces_. The rapid rotation of the top gives to all its
particles a tendency to _fly from the centre_. If the atoms of the wood
were not held together by the _attraction of cohesion_, they would fly
away in a circle outward from the top, _just as drops of water fly
off from a mop, while it is being twirled_. If you take a spoonful of
sand, salt, or dust, and drop it upon the top, it will be scattered in
a circle, just as the atoms of the top would be, _if they were free to
separate_, but not with the same force, because the atoms of the salt,
&c., not being in an active state of rotation, would only be influenced
_by momentary contact with the rotating body_. This tendency of the
particles of a rotating body to fly outward from the centre, is called
_the centrifugal force_.

     _Centrifugal._--From two Latin words meaning receding from the
     centre.

The other force influencing the top is _the attraction of gravitation_:
the attraction which, were the top not spinning, would draw it towards
the earth. The "spill" projecting from the bottom of the top _stands in
the line in which the top is drawn towards the earth_ and keeps it from
obeying the law of gravitation. Therefore the rotatory motion given to
the top, by the rapid unwinding of the string, and the tendency of its
atoms to fly outward, _balance the top_ upon the line in which it is
drawn to the earth, and which is occupied by the spill, which prevents
it falling to the ground.

815. _Why does a top first reel around upon the spill, then become
upright, and "sleep," and then reel again, and fall?_

[Illustration: Fig. 25.--PEG-TOP "REELING."]

Because, in being thrown from the hand, the top is delivered a little
out of the perpendicular, but the spill _is rounded off at the point_,
and when the top is rotating rapidly, the gravitative force which
attracts the top to the ground continually acting upon it, _draws the
weight of the top on to the extreme centre of the round point_. When
the rotation subsides, and the centrifugal force is weakened, then the
top _is no longer balanced upon the extreme point of the spill_, but
falls upon its sides, until the force of gravitation is exerted _beyond
the line of the spill_, upon the body of the top, and then it falls to
the ground.

[Verse: "Even a child is known by his doings, whether his work be
pure, and whether it be right."--PROVERBS XX.]

816. _Why does a top "sleep?"_

Because at that period of its spinning, which is called "sleeping," the
_centrifugal_ and the _gravitative forces_ acting upon the top, are
_nearly balanced_; and the top, obeying chiefly the _rotatory force_,
appears to be in a state of comparative rest.

817. _Why does the top cease to spin?_

Because _the friction of the air against its sides_, and the _friction
of the spill against the ground_, act in opposition to the _rotatory
force_, which is a temporary impulse applied by external means--the
hand of the person who spins it--and as soon as this _applied force_
is expended, the top yields to the law of gravitation, which is _a
permanent and ever-prevailing force_.

818. _Why does a marble revolve, as it is propelled along the ground?_

Because, in propelling the marble, _the thumb impels the upper surface
forward, and the finger draws the under surface backward_. This
gives a tendency to the upper and lower hemispheres of the marble
_to separate_, which they would do, but for the _cohesion of the
atoms_ of the marble. The upper part of the marble, therefore, rolls
forward, _drawing after it the under part_, which acquires a forward
motion by the force with which it is drawn upward, and in this way the
opposite portions of the marble act upon each other in the successive
revolutions.

When the marble strikes upon the earth, a new influence is exerted
upon it, which is _the friction of the earth_ upon the surface that
comes in contact with it; but the upper part of the marble, being free,
_overcomes the friction acting upon the lower part_, and thus the
marble continues to progress, until _the applied force which projected
it is expended_.

[Verse: "Better is a poor and a wise child, than an old and foolish
king who will no more be admonished."--ECCLESIASTES IV.]

819. _Why does a striped marble appear to have a greater number of
stripes when rolling, than when at rest?_

Because the stripes are presented in _rapid succession_ to the eye; and
as the eye receives _fresh impressions of stripes before the previous
impressions have passed away_, the stripes appear multiplied.

[Illustration: Fig. 26.--MARBLE AT REST.]

[Illustration: Fig. 27.--MARBLE ROLLING.]

820. _Why does a marble rebound when dropped upon the pavement?_

Because the force of its fall to the earth _compresses the atoms_ of
which the marble is composed; and the atoms then exert the force of
_elasticity to restore themselves to their former condition_; and by
the exercise of this force the marble is _repelled_, or _thrown upward
from the pavement_. Although a marble may be made of very hard stone,
yet that stone may be _elastic_, and possess, though in a much less
degree, _the same kind of elasticity which causes the India-rubber ball
to rebound from the earth_.

821. _Why does a marble, assuming it to be impelled with equal force,
roll further on ice than on pavement, and further on pavement than on a
pebble walk?_

Because the _friction_ is greater upon pavement than upon ice, and
greater upon a pebble walk than upon pavement.

822. _How many forces contribute to stay the progress of a rolling
marble?_

The friction of the _air_, the friction of the _earth_, and the
_attraction of gravitation_, which tends to bring all bodies to a state
of rest.

[Verse: "He shall turn the heart of the fathers towards the
children, and the heart of the children to their fathers."--MALACHI IV.]

823. _Why do the stripes upon a marble disappear when it is spun with
great velocity?_

Because, as in the case of the humming-top, the different parts of the
surface are _brought so rapidly in succession to the sight_, that they
_deface or confuse_ the impressions upon the retina.

[Illustration: Fig. 28--MARBLE SPINNING RAPIDLY.]

824. _Why are rings most perceptible at the opposite points, or poles,
of the marble?_

Because the point, or pole, _upon which the marble spins_, and that
which _corresponds to it_, on the upper surface, travel _less rapidly_
than the central portions, which being of a larger circumference, pass
through a greater amount of space, in the same period of time. The
stripes at the _poles_ of the marble, are, therefore visible, while
those at its _equator_ are imperceptible. (_See_ 522.)




CHAPTER XXXIX.


825. _Why are soap-bubbles round?_

Because they are _equally pressed upon all parts of their surface_ by
the atmosphere.

826. _Why are bubbles elongated when being blown?_

Because the _unequal pressure of the current of breath_ by which
they are being filled, alters the _relative pressure_ upon the outer
surfaces.

827. _Why does the bubble close, and become a perfect sphere, when
shaken from the pipe?_

Because the _attraction of cohesion_ draws the particles of soap
together, directly the bubble is set free from the bowl.

[Verse: "Children's children are the crown of old men; and the glory
of children are their fathers."--PROVERBS XVII.]

[Illustration: Fig. 29.--BLOWING SOAP BUBBLES.]

828. _Why do bubbles, blown in the sunshine, change their colours?_

Because the films of the bubbles constantly change in thickness,
through the atoms from the upper part descending towards the bottom,
and therefore the varying thickness of film _refracts, in different
degrees, the rays of light_.

829. _Why do bubbles burst?_

Because the atoms that compose their films _fall towards the earth
by gravitation_; the upper portion of the bubbles then _becomes very
thin_, and as the denser air of the atmosphere _presses towards the
warm breath within the bubble, it bursts the film_.

     _See_ 236, 237, _etc._, 501, _etc._

830. _Why do balloons ascend in air?_

Because the air or gas which they contain is _specifically lighter than
the atmosphere_; _the atmosphere, therefore, forces itself underneath
the balloon_, by its own tendency towards the earth, and the balloon is
thereby raised upwards. _A balloon is but a larger kind of bubble, made
of stronger materials._

831. _Why does an air-balloon become inflated when the spirit set upon
the sponge is lit?_

Because the _heat_ of the flame, and the _burning of the spirit_,
A, create a volume of _rarefied_, or _thin air_, which inflates the
balloon, and makes it _specifically lighter_ than the surrounding
medium.

[Verse: "A wise son heareth his father's instruction."--PROVERBS
XIII.]

832. _Why do balloons sometimes burst when they ascend very high?_

Because, as they get into the _thinner air_, which exists at _high
altitudes_, the gas within them expands, and the coating of the balloon
is burst asunder.

[Illustration: Fig. 30.--AIR-BALLOON.]

833. _Why does the gas of balloons expand in thin air?_

Because the air exerts a _less amount of pressure_ upon the air or gas
contained in the balloons.

834. _Why do parachutes fall very gradually to the ground?_

Because the _air_, coming in contact with the _under surface_ of the
expanded head of the parachute resists its downward progress.

[Illustration: Fig. 31.--PAPER PARACHUTE.]

835. _Why does a shuttlecock travel slowly through the air?_

Because the air acts upon the feathers of the shuttlecock, in the same
manner as it does upon the parachute--it strikes against their expanded
surface, and resists their progress through the air.

836. _Why does the shuttlecock spin in the air?_

Because the surfaces of the feathers fall upon the air _obliquely_, or
slantingly, and therefore, as the shuttlecock descends, it turns in the
air.

[Verse: "Come ye children, hearken unto me, I will teach you the
fear of the Lord."--PSALM XXXV.]

[Illustration: Fig. 32.--BATTLEDORE AND SHUTTLECOCK.]

837. _Why do we hear a noise when we strike the shuttlecock with the
battledore?_

Because the _percussion_ of the shuttlecock upon the parchment of the
battledore causes it to vibrate, and the vibrations are imparted to the
air.

838. _Why is the sound a dull and short one?_

Because the vibrations of the parchment are _not very rapid_, therefore
there is _little intensity_ in the vibrations of the air.

839. _Why does the exercise, afforded by playing battledore and
shuttlecock, make us feel warm?_

Because it makes us breathe _more freely_, and causes the _blood to
flow faster_; we, therefore, inhale more _oxygen_, which produces heat
by combining with the _carbon_ of our _blood_.

840. _Why does a kite rise in the air?_

A kite rises in the air by the force of the wind, which _strikes
obliquely_ upon its _under surface_. The string is attached to the
"belly-band" in such a manner that it is nearer the _top_ than the
_bottom_ of the band: this causes the bottom of the kite, when its
surface is met by the wind, to recede in the direction of the wind:
the top is accordingly _thrown forward_, and the kite is made to _lie
obliquely_ upon the current of air moving against it. The kite then
being _drawn by the string in one direction_, and _pressed by the
air in another direction_, moves in a line which _describes a medium
between the two forces acting upon it_.

[Verse: "Be ye therefore followers of God, as dear children; and
walk in love, as Christ also hath loved us."--EPHESIANS V.]

[Illustration: Fig. 33.--DIAGRAM EXPLAINING THE FLIGHT OF A KITE.]

841. _Why does the kite-string feel hot when running through the hand?_

Because the _rapid friction_ sets free the _latent heat_ of the
_string_, attracts the heat of the _hand_ to the spot where the
friction occurs, and sets free the latent heat of the _air_, which
follows the _string_ through the hand, and is compressed by the
friction.

842. _Why does running with the kite cause it to rise higher?_

Because it _increases the force_ with which the wind strikes upon the
surface of the kite. If a person were to _run with a kite at the rate
of five miles an hour, through a still air_, the effect would be _equal
to a wind flying at the rate of five miles an hour_ against a kite held
by a _stationary string_.

843. _Why does the flying-top rise in the air?_

Because its wings _meet the air obliquely_, just as the surface of the
kite does. And the _twirling of the top_, causing the oblique surfaces
of its wings to strike the air, produces _the equivalent effect of a
wind from the earth blowing the top upwards_.

[Verse: "Children obey your parents in the Lord: for this is right."]

844. _Why does the flying-top return to the earth when its rotations
are expended?_

Because the _reaction_ produced by its wings striking upon the air, is
insufficient to counteract the _attraction of gravitation_.

[Illustration: Fig. 34.--FLYING-TOP.]

[Illustration: Fig. 35.--PEA AND PIPE.]

845. _Why does a pea, into which a pin has been stuck, dance in
suspension upon a jet of air blown through a pipe?_

Because the jet of air, being _slightly compressed_ under the _convex_
form of the pea, by the weight of the pin, forms a _concave cup of
air_, in which the pea rests.

     In the case put, it is supposed that the pin is _passed through
     the pea_ until its head comes in contact with it. The pin is
     dropped into the hole of the pipe, and the breath is then applied,
     the pipe being held upright. The pea will rise in the air, and be
     suspended upon the jet, while the point of the pin will rotate
     around the stem of the pipe. There are other methods of fixing the
     pin which alter the result, and require a different explanation to
     that given above.




LESSON XL.


846. _Why does a mouse, painted upon one side of a card, and a trap
upon the other, represent to the eye a mouse in a trap when the card
is rapidly twirled upon a string?_

Because the image of the mouse is brought to the retina of the eye
before the image of the trap has passed away. The two impressions,
therefore, _unite upon the retina_, and produce the image of a mouse in
a trap.

[Verse: "Honour thy father and thy mother * * That it may be well
with thee, and thou mayest be long on the earth."--EPHESIANS VI.]

[Illustration: Fig. 36.--CARD WITH MOUSE-TRAP.]

[Illustration: Fig. 37.--REVERSE OF CARD WITH MOUSE.]

847. _Why will a bow stretched out of its natural position, propel an
arrow through the air?_

Because its substance, being _highly elastic_, the particles thereof
seek to restore themselves to their former state, as soon as the
resisting power is withdrawn. The _force_ derived from this elasticity,
is communicated to the arrow by the string against which it is placed.

848. _Why is the arrow propelled forward?_

Because the elasticity of the bow, _acting equally upon its two ends_,
to which the string is fastened, produce a line of force in a _diagonal
direction_. It thus illustrates the law, that _when a body is acted
upon by two forces at the same time, whose directions are inclined to
each other, it will not follow either of them, but will describe a line
between the two_.

849. _What forces tend to arrest the flight of the arrow?_

The _friction of the air_, and the _attraction of gravitation_.

[Verse: "My son, give, I pray thee, glory to the Lord God of Israel,
and make confession unto him."--JOSHUA VII.]

850. _Why are feathers usually fastened to the ends of arrows?_

Because the _greater friction_ of air acting upon them, opposes the
progress of that part of the arrow in a greater degree than it does the
other portion. The effect is, _to keep the point of the arrow forward_,
and in a straight line with its opposite extremity. If the arrow were
shot the reverse way from the bow, it would _turn round_, in the course
of its flight, in consequence of the friction of the air, offering
greater resistance to the progress of the feathered end.

[Illustration: Fig. 38.--BOW AND ARROW.]

[Illustration: Fig. 39.--JEW'S HARP.]

851. _Why does a Jew's harp give musical sounds?_

Because the _vibrations of the metal tongue_ are communicated to the
ear.

852. _Why will not the Jew's harp produce loud sounds unless it is
applied to the mouth?_

Because the vibrations are not very intense, but when it is blown upon
by the breath, the air is pressed upon it, and the vibrations are
thereby rendered more powerful.

853. _Why does the alteration of the arrangement of the mouth, affect
the formation of the sounds?_

Because it sends the air to the tongue of the harp in _a greater or
lesser degree of compression_.

[Verse: "Hear, ye children, the instruction of a father, and attend
to know understanding."--PROVERBS IV.]

854. _Why does the pressure applied to the handle of an air pistol
propel the cork?_

Because, between the cork A and the air-tight piston C, there is a
_closed chamber of air_ B. When the handle D, which moves the piston
C, is rapidly pushed in, it _compresses the air_ until it is so much
condensed, that it forces out the cork A.

[Illustration: Fig. 40.--AIR PISTOL, OR "POP-GUN."]

855. _Why must the handle be drawn out, before the cork is placed in?_

Because otherwise a partial _vacuum_ would be formed between A and C,
and there would not be sufficient air to force out the cork by the
return of the piston C D.

856. _Why does water rise in a syringe when the handle is drawn out?_

Because the pressure of the air on the water outside of the syringe,
forces it into the space vacated by the drawing up of the handle, and
where, otherwise, a _vacuum_ would be formed.

[Illustration: Fig. 41.--SYRINGE, WITH JET OF WATER.]

857. _Why does not the water run out when the syringe is raised?_

Because the pressure of the air upon the small orifice resists the
weight of the water.

858. _Why does the water leak out, but not run?_

Because water has a tendency always to _move to the lowest point_, but
as the air does not enter freely the water cannot escape. It therefore
_drops_, as small portions of the air enter.

[Verse: "Remember now thy creator in the days of thy
youth."--ECCLESIASTES XI.]

859. _Why cannot the handle be pressed in, if the finger is applied to
the orifice?_

Because water is not _compressible_, like air; it must therefore
escape before the handle can be pressed in. Air may be forced into a
much smaller compass than is natural to it; but it is impossible to
_compress water_ in any great degree.

[Illustration: Fig. 42.--"SUCKER."]

[Illustration: Fig. 43.--HOOP.]

860. _Why does a "sucker" raise a stone?_

Because underneath the sucker _a vacuum_ is formed and the external
air, pressing on all sides _against the vacuum_, lifts the stone. The
term "sucker" is founded upon the mistaken notion that the leather
"sucks," or "draws" the stone. That such is not the case is evident:
if, when the stone is suspended, a pin's point be passed under the
leather, so as to open a small passage for the air, the stone will
_drop instantly_.

861. _Why does a hoop roll, without falling to the ground?_

Because the _centrifugal force_ gives it a motion which is called the
_tangent to a circle_--that is, a tendency in all its parts _to fly off
in a straight line_. When a piece of clay adhering to the hoop flies
off, it leaves the hoop in a line which is straight with the part of
the surface from which it was propelled; this line is _the tangent to
the circle of the hoop_; and the tendency of all the parts of the hoop
to fly off in this manner, counteracts the attraction of the earth, so
long as the hoop is kept in motion.

[Verse: "Children obey your parents in all things: for this is
well-pleasing unto the Lord."--COLOSSIANS III.]

862. _Why does the hoop, in falling, make several side revolutions?_

Because its onward movement, not being quite expended, influences the
_centre of gravity of the hoop_, and changes its line of direction. The
hoop is also elastic, and when its sides strike the earth, they spring
up again, and continue turning until the opposing forces are overcome
by the _attraction of gravitation_.

863. _Why will a little boy balance a large boy on a see-saw?_

Because the "see-saw" may be placed so that its ends are at _unequal
distances from the centre_. This gives the little boy the power of
_leverage_, by which is meant the increase of power, or weight, by
_mechanical means_.

[Illustration: Fig. 44.--BOYS AND "SEE-SAW."]

864. _Why does the little boy sink to the ground when the larger boy
slightly kicks the earth?_

Because the larger boy, by kicking against the earth, opposes by
mechanical force the _attraction of gravitation_ acting upon him, and
he becomes _temporarily_ less attracted to the earth than the little
boy.

865. _Why can the little boy, if he choose, keep the big boy up, when
once he is up?_

Because, as the big boy is then on _an inclined plane_ with the
_fulcrum_, or centre upon which the see-saw moves, the arm of _the
lever_, upon which the big boy sits, is _relatively shortened_, and he
has then _less mechanical power_. Also, a portion of the weight of the
larger boy is transmitted along the lever _to the arm upon which the
little boy sits_.

[Verse: "Little children, let no man deceive you: he that doeth
righteousness is righteous, even as he is righteous."--1 JOHN III.]

[Illustration: Fig. 45.--TRAP AND BALL.]

866. _Why is the ball propelled upward, in the game of trap and ball,
when the trigger is struck?_

Because, when the trigger is struck at A, it is forced downwards,
turning upon the fulcrum B, the opposite end, forming the spoon, is
thereby forced upwards, describing a small _arc_, or curved line; but
directly the ball is set free from the spoon, it rises in a _right
line_ with the _direction it was taking, at the moment it was set free_.

[Illustration: Fig. 46.--BAT AND BALL.]

867. _What principles of natural philosophy are illustrated by the
results of bat and ball?_

_Percussion_, when the bat strikes the ball; _rotatory motion_,
when the ball is sent whirling away; _momentum_, which it acquires
by velocity; _elasticity_, when it rebounds from an object against
which it strikes; _reflected motion_, when it is turned by a body
upon which it impinges; _friction_, as it rolls along the ground; the
_communication of force_, when it sets another body in motion against
which it strikes; _gravitation_, when it falls to the earth; and
_inertia_, when it lies in a state of rest.

[Verse: "A wise son makes a glad father: but a foolish son is the
heaviness of his mother."--PROVERBS X.]

868. _Why do pith-tumblers always pitch upon one end?_

Because the _lead_ B is _specifically heavier_ than the _pith_ to
which it is attached; it therefore always falls undermost; and as the
lead is rounded off, just like the spill of a top, after the head has
oscillated a little, and expended the force of the momentum of its
fall, it will settle upon its _centre of gravity_, or the point through
which it is _attracted to the earth_.

[Illustration: Fig. 47. PITH-TUMBLER.]

869. _Why do the figures upon the "Thaumatrope" appear to dance, when
they are made to revolve before a mirror?_

Because the eye, in looking through the holes in the card, towards
the reflections in the mirror, receives a _rapid succession of
impressions_. As the figures upon the card are represented in a
graduated series of positions--the _first_ one standing upright, the
_second_ with his knees a little bent, the _third_ a little more bent,
as in the act of springing, and so on, the _figure_ being in each case
_the same_, but the position _slightly altered_, imparts an impression
to the mind, through the eye, that _one figure_ is passing through a
_series of motions_.

     _Thaumatrope._--From two Greek words, meaning _wonder_ and _to
     turn_.

     We have said enough, we hope, to show that even the play-hours of
     children may be made instructive to them; and that the simplest
     toys may be used to illustrate some of the grandest laws of
     nature. Nor may this kind of instruction be confined to children
     alone. Grown-up people, whether participators in the sports of
     youth, or simple observers of their games, may gain instruction
     for themselves, and be the better teachers of their children, by
     taking an interest in their enjoyments, and giving to their minds,
     through the attractiveness of pastime, a taste for observing and
     estimating the varied phenomena which present themselves.

[Verse: "Jesus said, Suffer little children, and forbid them not, to
come unto me; for of such is the kingdom of heaven."--MATTHEW XIX.]

     Moreover, we think that parental government acquires a greater
     power when it leans towards the natural desires of childhood, and
     wins those desires into a proper direction. Love existing between
     parent and child is the best tie to home, and the strongest
     incentive to duty. There is also something in the gentleness of
     childish nature which may influence for good the sterner mould of
     man, too often warped and clouded by the cares of life.

[Illustration: Fig. 48.--THAUMATROPE, OR "WONDER-TURNER."]

     In Kay's "Life of Sir John Malcolm," we find an admirable and apt
     passage. Sir John says:--"I have been employed these last few
     hours with John Elliot, and other boys, in trying how long we
     could keep up two cricket-balls. Lord Minto caught us. He says
     he must send me on a commission to some very young monarch, for
     that I shall never have the gravity of an ambassador for a prince
     turned of twelve. He, however, added the well-known and admirable
     story of Henry IV. of France, who, when caught on all fours
     carrying one of his children, by the Spanish envoy, looked up and
     said, 'Is your excellency married?' 'I am, and have a family,' was
     the reply. 'Well, then,' said the monarch, 'I am satisfied, and
     shall take another turn round the room,' and off he galloped, with
     his son on his back flogging and spurring him. I have sometimes
     thought of breaking myself of what are termed boyish habits; but
     reflection has satisfied me that it would be very foolish, and
     that I should esteem it a blessing that I can find amusement in
     everything, from tossing a cricket-ball, to negotiating a treaty
     with the Emperor of China. Men who will give themselves entirely
     to business, and despise (which is the term) trifles, are very
     able, in their general conception of the great outlines of a plan,
     but they feel a want of knowledge, which is only to be gained by
     mixing with all classes in the world, when they come to those
     lesser points upon which its successful execution may depend."

[Verse: "Whether therefore ye eat, or drink, or whatsoever ye do, do
all to the glory of God."--CORINTH. X.]




CHAPTER XLI.


869. _Why do we eat food?_

Because the atoms of which our bodies are composed are _continually
changing_. Those atoms that have fulfilled the purposes of nature are
removed from the system, and, therefore, new matter must be introduced
to supply their place.

870. _Why do we eat animal and vegetable food?_

Because their substances are composed of _oxygen_, _hydrogen_,
_carbon_, and _nitrogen_--the four chemical elements of which the human
system is formed. They are, therefore, capable of nourishing the body,
after undergoing digestion.

871. _Why do we masticate our food?_

Because mastication is _the first process towards the digestion of
food_. Before animal or vegetable substances can nourish us, their
condition must be entirely changed, their _organic_ states must be
dissolved, and they must become simple matter, in a homogeneous mass,
consisting of the four chemical elements necessary to nutrition, and
they must again be restored to an organic condition.

872. _Why does saliva enter the mouth when we are eating?_

Because, in addition to the _mechanical_ grinding of the food by the
action of the teeth, it is necessary that it should undergo certain
chemical modifications to adapt it to our use. There are placed,
therefore, in various parts of the body, _glands_, which secrete
peculiar fluids, that have a chemical influence upon the food.

The first of these glands are the _salivary glands of the mouth_, which
pour out a clear watery fluid upon the food we eat, and which fluid has
been found to possess a property which contributes to the digestion of
food.

The moisture afforded by the salivary secretion is also necessary to
enable us to swallow the food.

[Verse: "And the Lord said unto him, Who hath made man's mouth?
or who maketh the dumb, or the seeing, or the blind? have not I the
Lord?"--EXODUS IV.]

873. _Why does the salivary juice enter the mouth just at the moment
that we are eating?_

Because the glands, which are buried in the muscles of the mouth, and
which in their form are much like bunches of currants, are always full
of salivary secretion. There are nerves which are distributed from the
brain to these glands, and when other nerves which belong to the senses
of taste, of sight, or of feeling, are excited by the presence of food,
_a stimulus_ is imparted to the salivary glands, through the nerves
that surround them, their cells collapse, and the juice which they
contain is poured out through their stems, or ducts, into the mouth.

874. _How do we know that impressions imparted to one set of nerves,
may be imparted to another set, so as to put any particular organ in
action._

Because very frequently _the mere sight_ of rich fruit, or acid
substances, _will cause the saliva to flow freely_. In this case it
is evident that the salivary glands _could not see or know_ that such
substances were present. An impression must, therefore, be made upon
the brain, _through the organ of vision_, and the desire to taste the
substances being awakened, a nervous stimulus is _imparted to the
glands of the mouth_, and they at once commence their action, _as if
food were present_.

875. _Why does food descend into the stomach?_

Because, after the teeth, the tongue, and the muscles of the mouth
generally, have rolled the food into a soft bolus, it is conveyed to
the back of the mouth, where it is set upon the opening of the throat
(_oesophagus_). It does not then descend through the throat by its own
gravity, because the throat is generally in a compressed or collapsed
state, like an empty tube; and we know that persons can eat or drink
when with their heads downwards. The oesophagus is formed of a number
of muscular threads, or rings, and _each little thread is like a hand
ready to grasp at the morsel that is coming_. As soon as the bolus is
presented at the top of the throat, these little muscular hands lay
hold of it, and transmit it downward, passing it from one to another,
until it is conveyed through the long passage, to the door of the
stomach, which it enters.

[Verse: "Remove far from me poverty and lies; give me neither
poverty nor riches; feed me with food convenient for me."--PROVERBS
XXX.]

[Illustration: Fig. 49.--SECTION OF THE STOMACH, &c.]

     A. The inner coat of the _stomach_. (The stomach is here
     represented cut through its length, so that we can see its inside.)

     B. The lower extremity of the throat, or _oesophagus_, through
     which food enters the stomach.

     C. The passage out of the stomach, called the _pylorus_, where a
     muscular contraction prevents the escape of undigested food.

     D. The _duodenum_, and the ducts through which the _bile_ and
     _pancreatic_ juices enter and mingle with our food.

876. _Why do we not feel the food being transmitted through the throat?_

Because the nerves of the body differ in their powers: some are
nerves of _feeling_, some of _motion_, and others are nerves of the
_senses_. The nerves of feeling are most abundantly distributed to
those parts _where feeling is most useful and necessary to us_. But the
faculty of feeling our food undergoing digestion would be no service
to us whatever; therefore the nerves of _motion_ are plentifully
distributed to the throat and stomach, but very few of the nerves of
_feeling_--just as many as will tell us when we eat anything _too hot_,
or _too cold_, or that the stomach is _out of order_.

877. _Why do we feel uneasy after eating to excess?_

Because the stomach is _distended_, and presses upon the other organs
by which it is surrounded.

[Verse: "Who satisfieth thy mouth with good things; so that thy
youth is renewed like the eagles."--PSALM CIII.]

878. _Why do we feel drowsy after eating heartily?_

Because, while the stomach is in action, _a great proportion of the
blood of the body is drawn towards it_, and as the blood is withdrawn
from the other parts of the body, they fall into a state of languor.

879. _Why does blood flow more freely to the stomach during digestion?_

Because the energy of an organ is _increased by the flow of blood_,
which supplies the _material_ of which our organs are composed, and in
which the _vital essence_, supporting life, resides.

880. _Why does excess in eating bring on indigestion?_

Because the power of the stomach to digest food is _governed by the
amount of food required by the system_. It seems to be an instinct of
the stomach to hold back food which is in excess, and by indications
of pain and disturbance to warn its master that _excess has been
committed_.

881. _Why is food digested in the stomach?_

Because it enters the stomach in the form of a paste, produced by the
action of the mouth; and directly food enters, the _gastric juice_,
which is formed by glands embedded in the coats of the stomach,
trickles down its sides. This is a more _powerful solvent_ than the
salivary juice--it is like the same kind of fluid, only much stronger,
and it soon turns the food from a rough and crude _paste_ into a
_greyish cream_ (chyme). The heat of the stomach assists the operation,
and the muscular threads of the coats move the cream along, in the same
manner that the muscles of the oesophagus brought down the food.

The cream is passed towards the door which leads outward from the
stomach (_pylorus_); but if, in the midst of the cream, there are any
undissolved particles of food, it closes upon them, and they return
again to the stomach to be further changed.

[Verse: "When thou hast eaten and art full, then thou shalt bless
the Lord thy God for the good land which he hath given thee."--DEUT.
VIII.]

882. _Why does indigestion bring on bilious attacks?_

Because the _liver_ secretes a fluid to assist in the digestion of
food. The liver is a gland--a similar organ to the glands of the
mouth--and it forms _bile_ in the same manner that they form the
salivary juice. Only the liver is a _much larger gland_, and a much
greater quantity of blood passes through it. The liver pours its
secretion into the biliary duct (Fig. 49) to mix with the grey cream
as it passes onward, and to further dissolve it. But when the stomach
is excited by food which it cannot dissolve, and when the owner of the
stomach, disregarding its remonstrances, will persist in over-eating,
or in eating things that disagree with the system, then _the liver
and the stomach sympathise_, and the muscular threads, or hands, that
prevail all through the alimentary organs, instead of moving _onward_,
move backward, and _throw some bile into the stomach_ to assist to
dissolve and remove the excessive or improper food.




CHAPTER XLII.


883. _Why does some portion of the food we eat nourish the system,
while other portions are useless?_

Because most food contains some particles that are indigestible, or
that, if digested, are innutritious, and not necessary for the system.
The _liver_ is the organ by whose secretion the _useful is separated
from the useless_; for when the bile enters through the duct (Fig. 49)
and mixes with the grey cream coming from the stomach, it remains no
longer a grey cream, but turns into a mass coloured by bile, having
upon its surface _little globules of milk_, small, but very white.
Those minute globules of milk (_chyle_) are the nutritious particles
derived from the food; the other portion, coloured with bile, is the
useless residue, or rather the _bulk from which the nutrition has been
extracted_.

[Verse: "God hath made of one blood all nations of men for to dwell
on all the face of the earth."--ACTS XVII.]

884. _Why does the milky, or nutritious matter, separate from the
innutritious, upon admixture with bile?_

Because the bile contains an oily matter which _repels_ the watery
_milk of nutrition_.

The _pancreatic juice_ also enters through the same duct with the bile.
But its precise use is not understood. It is a fluid much like the
salivary secretion of the glands of the mouth.

[Illustration: Fig. 50.--GREAT VESSELS OF THE CIRCULATION, AND THE DUCT
WHICH CONVEYS NUTRITIVE MATTER TO THE BLOOD.]

     A B. _Jugular veins_ which return blood from the head to the heart.

     C. The _superior venæ cava_, or trunk vein, which pours the blood
     returned from the upper part of the system into the heart. There
     is a similar large vessel which meets this one and brings back
     blood from the lower part of the body, and they both pour the
     blood into the right side of the heart.

     D E. The branches of the _venous system_ which bring back the
     blood from the arms.

     F F. The _great aorta_, the blood vessel which conveys arterial
     blood from the heart, and gives off branches that supply every
     part of the body.

     G. Another large vein which returns the blood from the muscles of
     the chest, &c.

     H H. The _thoracic duct_, which receives the newly dissolved food
     from the small absorbents, that collect it from the intestines. It
     conveys this nutrition (called chyle) upward along the back, until
     it reaches where the duct turns into the junction of two veins,
     and pours its contents into the veins bringing blood back to the
     heart. The nutrition, therefore, is at this moment mixed with the
     venous blood, and is sent to the lungs to be oxygenised.

[Verse: "But now hath God set the members in the body, every one as
it pleased him."--1 CORINTHIANS XII.]

885. _How is the nutrition taken away from the bilious residue?_

The muscular threads (or hands, as we figuratively call them) continue
to push forward the digested matter through a long tube, called _the
alimentary canal_, or bowels. This canal is some thirty feet in length,
and is folded in various layers across the abdomen, and tied to the
edge of a sort of apron, which is gathered up and fastened to the
back-bone. All along this alimentary canal those muscular hands are
pushing the digested mass along. But upon the coat or surface of the
canal there are millions of little vessels called _lacteals_, which
look out for the minute globules of milk as they pass, and _absorb_
them, which means that they pick them up, and carry them away. There is
an immense number of these little vessels, all busily at work picking
up food for the system.

Then there is a large vessel, called the _thoracic duct_, which comes
down and communicates with those little vessels (it is a sort of
overseer, having a large number of workmen,) and collects the produce
of their toil, and carries it upwards to the part where it passes _from
the organs of digestion_ into the _vessels of circulation_.

886. _What becomes of the nutrition, when it has entered the vessels of
the circulation?_

It is sent through a large vein into _the heart_, entering that organ
on the right side, from which the heart propels it into the lungs,
mixed with _venous blood_; and the venous, or blue blood, is sent into
the lungs, _taking with it the milk_, the formation of which we have
traced.

887. _Why are the venous blood and the chyle sent to the lungs?_

Because the venous blood, in its circulation through the body, has
parted with its _oxygen_, and taken up _carbon_, and it requires _to
get rid of the carbon, and take up more oxygen_. The chyle, also, now
combined with the blood, requires _oxygen_, and having obtained it, is
converted into _bright red blood_, and the blue blood of the veins,
having got rid of its carbon, which formed the carbonic acid of the
breath, has again become _bright red blood_. We must therefore, in
pursuing our description, cease to speak of blue, or _venous blood_,
and of white milk, or _chyle_, for the two have now combined, and, with
the oxygen of the air, have formed _arterial blood_.

[Verse: "My flesh and my heart fainteth; but God is the strength of
my heart, and my portion for ever."--PSALM LXXIII.]

888. _What becomes of the arterial blood thus formed?_

It is sent back from the lungs to the right side of the heart, from
which it is sent into the _great trunk of the aorta_, and from thence
it passes into smaller blood-vessels, until it finds its way to _every
part of the system_.

[Illustration: Fig. 51.--THE ORGANS OF RESPIRATION.]

     A. The _heart_.

     B B. The _lungs_.

     C. The _aorta_, and on either side of the aorta the vessels which
     convey the venous blood to the lungs to be _oxygenised_, and the
     corresponding vessels which return it to the heart, after it has
     undergone that operation. (For _aorta_ _see_ Fig. 50.)

     D. The _trachea_, or large air passage, through which the air
     passes into the spongy texture of the lungs, when we breathe.

     E E. _Arteries_ and _veins_, being the trunks of the vessels that
     supply the head, &c.

889. _Why does the chest expand when we breathe?_

Because the lungs consist of _millions of hollow tubes_, and _cells_,
which, having been emptied by throwing off _carbonic acid gas_ and
_nitrogen_, become compressed, and the atmospheric air flowing into
these millions of spaces, and filling the lungs, just as water fills
and swells a sponge, causes them to expand, and occupy greater room.

[Verse: "All the while my breath is in me, and the spirit of God is
in my nostrils. My lips shall not speak wickedness, nor my tongue utter
deceit."--JOB XXVII.]

890. _How does the blood communicate with the air in the lungs?_

Through the _sides of very minute vessels_, of which, perhaps, a _fine
hair_ gives us the best conception. But these vessels are _twisted
and wound round each other_ in such a curious manner, that they form
_millions of cells_, and by being twisted and wound, a much _greater
surface of air and blood_ are brought to act upon each other, than
could otherwise be accomplished.

891. _Why does the blood which is thus formed, impart vitality to the
parts to which it is sent?_

Because the blood is itself _vitalised_--is, in fact, _alive_, and
capable of diffusing life and vitality to the organisation of which it
forms a part.

This is a very wonderful fact, but no less true than wonderful, that
dead matter which, but a little while ago, was being ground by the
teeth, softened by the saliva, and solved by the gastric juice and
bile, has now acquired _life_. Nobody can tell the precise stage or
moment when it began to live. But somewhere between the stomach and the
lungs, melted by the gastric juice, softened by the secretion of the
pancreas, separated by the bile of the liver, macerated by the muscular
fibres of the bowels, taken up by the absorbents, warmed by the heat of
the body, and ærated in the lungs, it has by one, or by all of these
processes combined, been changed from the dead to the living state, and
now forms part of the _vital fluid of the system_.




CHAPTER XLIII.


892. _Why do we know that the blood has become endowed with vital
powers?_

Because, in the course of its formation, it has not only undergone
change of condition and colour; but, if examined now by the microscope,
it will be found to consist of millions of minute cells, or discs,
which float in a watery fluid. The paste produced by mastication
consisted of a crude admixture of the atoms of food; the cream
(_chyme_) formed from this in the stomach, presents to the microscope
a heterogeneous mass of matter, exhibiting no appearance whatever of
a new organic arrangement; the milk (_chyle_) which is formed in the
intestines is found to contain a great number of very small molecules,
which probably consist of some fatty matter; as the chyle progresses
towards the _thoracic duct_ (Fig. 50), it appears to contain more
of these, and slight indications present themselves of the approach
towards a new organic condition.

But wherever _vitalisation begins_, no human power can say with
confidence. Yet there can be no doubt that the blood is both
_organised_ and _vitalised_, and that it consists of corpuscles, or
little cells, enclosing matters essential to life.

[Verse: "But they that wait upon the Lord shall renew their
strength; they shall mount up with wings as eagles; they shall run and
not be weary; and they shall walk and not faint."--ISAIAH XL.]

893. _Why does the blood circulate?_

Because all the bones, muscles, blood-vessels, nerves, glands,
cartilages, &c., of which the body is composed, are constantly
undergoing a _change of substance_. It is a condition of their life,
health, and strength, that they shall be "_renewed_," and the blood is
the great source of the _materials_ by which the living temple is kept
in repair.

894. _How is the body renewed by the blood?_

Every drop of blood is made up of a large number of corpuscles, each
of which contains some of the elements essential to the wants of the
system.

Let us, to simplify the subject, consider the blood vessels of the body
to be so many _canals_, on the banks of which a number of inhabitants
live, and require constant sustenance. The corpuscles of the blood are
the _boats_ which are laden with that sustenance, and when the heart
beats, it is a signal for them to start on their journey. Away they
go through the arch of the great _aorta_, and some of the earliest
branches which it sends off convey blood to the arms. We will now for a
moment dismiss the word _artery_, and keep up the figure of a system of
canals, with a number of towns upon their banks.

Well, away go a fleet of boats through the _aorta_ canal, until they
reach a point which approaches Shoulder-town; some of the boats pass
into the _axillary_ canal and Shoulder-town is supplied; the other
boats proceed along the _humeral_ canal until they approach Elbow-town,
when another division of the boats pass into other branch canals and
supply the wants of the neighbourhood; the others have passed into
the _ulnar_ canals and the _radial_ canals until they have approached
Wrist-town and Hand-town, which are respectively supplied; and then
the two canals have formed a junction across the palm and supplied
Palm-town, where they have given off branches and boats to supply the
four Finger-towns, and Thumb-town.

[Verse: "Though hand join in hand, the wicked shall
not be unpunished; but the seed of the righteous shall be
delivered."--PROVERBS XXI.]

[Illustration: Fig. 52.--ILLUSTRATION OF THE SYSTEM OF CANALS THAT
SUPPLY THE FORE-ARM WITH BLOOD.]

     Between A and B the _brachial canal_, which gives off branches to
     supply Elbow-town, &c., and then divides into two main courses,
     diverging to the opposite sides of the arm, and sending a smaller
     canal down the centre.

     D D. The point where the _ulnar canal_ and the _radial canal_,
     after having passed and supplied Wrist-town, form a junction,
     running through Palm-town, and in their course giving off branches
     to supply the four Finger-towns and Thumb-town.

     _For further explanations of the engraving, see 57._

895. _How does the blood return to the lungs, after it has reached the
extremities?_

The _veins_ constitute a system of vessels corresponding to the
arteries. We may say that the arteries form _the down canal_, and the
veins _the up canal_. The arteries, commencing in the great trunk of
the _aorta_, branch off into large and then into smaller tubes, until
they form _capillary_ or hair-like vessels, penetrating everywhere.

[Verse: "As for man his days are as grass; as a flower of the field
so he flourisheth."--PSALM CIII.]

_The capillary extremities of the arteries, unite with the capillary
extremities of the veins,_ and the blood passes from the one set of
vessels into the other. As the _arteries become smaller_ from the point
where they receive the blood, so the _veins grow larger_; the venous
capillaries, pour their contents into small vessels, and these again
into larger ones, until the great _venous_ trunks are reached, and the
blood is passed again into the heart as at first described. (Fig. 50.)

896. _Why do we see blue marks upon our arms and hands?_

Because large veins lie underneath the skin, through which the blood of
the fingers and hand is _conveyed back to the heart_.

897. _Why are the veins more perceptible than the arteries?_

Because the arteries are buried _deeper in the flesh, for protection_.
It would be _more dangerous to life to sever by accident an artery
than a vein_. A person might bleed longer from a vein than from an
artery, without endangering life; because the arteries supply the _life
sustaining blood_. The Almighty, therefore, has buried the arteries for
safety.

898. _Why when we prick the flesh with a needle does it bleed?_

Because the capillary arteries and veins are so fine, and are so
thickly distributed all over the body, that not even the point of a
needle can enter the flesh without penetrating the coats of several of
these small vessels.

[Verse: "Let every thing that hath breath praise the Lord. Praise ye
the Lord."--PSALM CL.]

899. _What occurs during the circulation of the blood?_

Not only do the various parts to which the boats are sent take from
them whatever they require, but _the boats collect all those matters
for which those parts have no further use_. The bones, the nerves, the
muscles, &c., all renew themselves as the boats pass along; and all give
something to the boats to bring back. One of the chief exchanges is
that of _oxygen_ for _carbon_, by which a gentle _heat_ is diffused
throughout the system. It is for this purpose that _fresh air_ is so
_constantly necessary_.

But other exchanges take place. The blood, in addition to oxygen and
carbon, contains _hydrogen_ and _nitrogen_. But it contains its four
elements in _various forms of combination_, producing the following
_materials_ for the use of the body: of 1,000 parts of blood, _about_
779 are _water_; 141 are _red globules_; 69 are _albumen_; 3 are
_fibrin_; 2 are _fatty matter_; 6 are various _salts_.

Albumen and fibrin are a kind of flesh imperfectly formed, and probably
are chiefly used in repairing the muscles. The red corpuscles contain
the oxygen which goes to combine with the superabundant carbon, and
develop heat; the fatty matters probably repair the fatty tissues, and
glands that are of a fatty nature; and the various salts contribute to
the bones, and to the chemical properties of those secretions which
are formed by the glands, &c., while the great proportion of water is
employed in cleansing, softening, and cooling the whole, or the living
edifice, and it is the medium through which all the nutrition of the
body is distributed.

900. _Why do we feel the pulse beat?_

Because every time that the heart contracts it send a fresh supply of
blood to the blood-vessels, and the motion thus imparted creates _a
general pulsation throughout the system_: but it is more distinctly
perceived at the pulse, because there a rather _large artery lies near
to the surface_.

[Verse: "Thy hands have made me and fashioned me: give me
understanding, that I may learn thy commandments."--PSALM CXIX.]

901. _What becomes of the matter collected by the blood in the course
of its circulation?_

We have already explained that carbon is thrown off from the lungs in
the form of carbonic acid gas. But there are many other matters to be
separated from the venous blood, and its purification is assisted by
the action of the liver, which is supplied with a large vein, called
the _portal vein_, which conveys into the substance of the liver, a
large proportion of the venous blood, from which that organ draws
off those matters which form the bile, and other matters which are
transmitted with the bile to the bowels. The _liver_ and the _lungs_,
therefore, are the great purifiers of the venous blood. But there are
also smaller organs that assist in the same work.

[Illustration: Fig. 53.--SHOWING THE DISTRIBUTION OF BLOOD THROUGH
BRANCHES OF THE AORTA.]

     A. The _aorta_.

     B. Branches given off for the _aorta_ to supply one portion of the
     intestines.

     C. Branches given off by the aorta to supply other portions of the
     intestines. A complete communication may be traced between these
     vessels from the origin of one to that of the other.

     D. The _pancreas_, or sweetbread, a large gland that forms the
     pancreatic juice, which it pours in through the duct. (_See_ Fig.
     50.)

     E E E. The _large intestines_, forming the termination of the
     alimentary canal.




CHAPTER XLIV.


902. _Why when we cut our flesh does it heal?_

Because the blood coagulates over the cut, and throws out a kind of
_lymph_, which forms an incipient flesh, and excludes the air while the
blood-vessels are engaged in _repairing the part_.

[Verse: "And God said, Let us make man in our own image, after our
likeness; and let them have dominion over the fish of the sea, and over
the fowl of the air, and over the cattle, and over all the earth, and
over every creeping thing."--GEN. I.]

903. _Why, since all the substance of the body undergoes change, do we
preserve the same features throughout our lives?_

Because our substance changes in the _minutest atoms_; and each
separate atom has a life of itself, the maintenance of which preserves
the _unity and permanence of the whole_.

904. _Why do moles upon the skin continue permanent, while bruises and
wounds disappear?_

Because moles are themselves _organised formations_, and repair
themselves just as any other part of the body does. But bruises and
wounds are the result of _accidental disturbances_, which in course of
time become removed.

905. _Why do the marks of deep cuts sometimes remain?_

If the cut is so deep and serious as to destroy the _system of vessels_
which supply and repair the part, then it is evident that they cannot
work so perfectly as when in their sound condition. Their functions
are, therefore, interfered with, and instead of having flesh uniform
with the other parts of the system; there results a _scar_, or a wound
_imperfectly repaired_.

906. _Why when we hold our hands against a candle-light do we perceive
a beautiful crimson colour?_

Because the fluids and vessels of the body are in some degree
transparent, and the thin textures of the sides of the fingers allows
the light to pass, and shows the beautiful crimson colour of the blood.

     If the web of a frog's foot be brought in the field of a good
     microscope, and set against a strong light, the blood may be seen
     in circulation, with the most wonderful effect. Each vessel, and
     every globule of blood, can be seen most distinctly, and the
     junction of the arteries and veins can be clearly traced. The
     little boats of nutrition may be seen chasing each other in rapid
     succession, and when the animal exerts itself to escape, the
     flow of the blood increases; and not unfrequently, under these
     circumstances of agitation, have we seen two or three blood discs
     struggling together to enter a vessel that was too small for them.
     Again and again they have endeavoured to find a passage, until
     one of them happening to slip forward, got away, followed by the
     others!

[Verse: "Know ye that the Lord he is God: it is he that hath made
us, and not we ourselves: we are his people, and the sheep of his
pasture."--PSALM C.]

907. _Why does the flesh underneath the nails look red?_

Because the transparent texture of the nails enables us to see the
colour of the _vascular structure_ that lies underneath the skin.

     _Vascular_.--Full of vessels. In this instance, full of capillary
     blood-vessels.

908. _Why have we nails at our fingers' ends?_

Because they give _firmness to the touch_, and enable us to apply the
extremities of the fingers to many useful purposes for which they
would otherwise be unfitted. They enable us to _press the tips of the
fingers_, where the highest degree of sensitiveness prevails, so as
to bring _the largest amount of nervous perception_ into the sense of
touch.

909. _Why do white spots occur upon the nails?_

Because the vascular surface underneath is attached to the horny
texture of the nail; but by knocks and other causes, the nail sometimes
_separates in small patches from the membrane_ below, and becomes _dry
and opaque_.

910. _Why is there a circular line of whitish colour at the root of the
nail?_

Because there the nail is _newly formed_ by the vascular substance
out of which it grows, and has not yet assumed its proper horny and
transparent nature.

911. _Why is the eyeball white?_

Because the blood-vessels that supply its surface are so very fine that
they do not admit the _red corpuscles_ of the blood.

912. _Why does the eyeball sometimes become blood-shot?_

Because, under exciting causes of inflammation, the _blood-vessels
become distended_, and the red corpuscles enter, producing a net-work
of red blood-vessels across the white surface of the eye.

913. _Why are the lips red?_

Because the lips are formed of the _mucous membrane_ that lines the
body internally, and covers the surface of most of the internal parts.
This membrane contains a great number of minute red vessels, which give
softness and moisture to the surface. A very beautiful illustration
of the softness, moisture, and delicate colour of the mucous membrane
is afforded by turning up and examining the under surface of the upper
eyelid.

[Verse: "Hast thou not known, hast thou not heard, that the
everlasting God, the Lord, the Creator of the ends of the earth,
fainteth not, neither is weary? there is no searching of his
understanding"--ISAIAH XL.]

914. _Why do delicate persons look pale and languid?_

Because, generally from the want of exercise and fresh air, their blood
is deficient of the healthy proportion of _red corpuscles_.

915. _Why does exercise and fresh air impart to healthy persons a red
and fresh appearance?_

Because the redness of the blood is due to the _amount of oxygen_ which
it contains, and air and exercise _oxygenise_ the blood, and diffuse it
throughout the system.

916. _How is the blood propelled through the arteries?_

By the very powerful contraction (and alternate dilation) of the thick
_muscles of the heart_, assisted also by the _muscular cords of the
blood-vessels_ themselves, and in many instances by the _compression of
the muscles_ in which the arteries lie embedded.

917. _Why are the capillary arteries capable of receiving the great
quantity of blood sent out through the larger vessels?_

Because the capillary vessels are _so numerous_, that though they are
infinitely smaller, they are capable of receiving in their minute tubes
_the whole of the quantity of blood_ transmitted to them through the
larger vessels.

918. _Why, when we sit with our legs crossed, do we see the foot that
is raised move at regular intervals?_

Because the pressure upon the muscles of the leg retards the progress
of the blood until it forces _itself through the compressed vessels_,
and thereby imparts a pulsation which moves the leg and foot.

919. _Why are capillary blood-vessels found in every part of the
system?_

Because it is _through these small vessels alone_ that the substances
of the body are renewed and changed. Even the larger blood-vessels _do
not sustain themselves upon the blood which they contain_, but receive
into their coats numerous capillary vessels by which they are nourished.

[Verse: "All my bones shall say, Lord, who is like unto thee, which
deliverest the poor from him that is too strong for him, yea, the poor
and the needy from him that spoileth him?"--PSALM XXXV.]

920. _How much blood does the human body contain?_

From _twenty-five_ to _thirty-five_ pounds. (_See_ 623.)

921. _How does the blood ascend in the veins, in opposition to
gravitation?_

In addition to the muscular coats of the veins, and the influence
of muscular action upon them, there are in the veins numerous
semi-circular valves, which are not found in the arteries. These valves
extend from the sides of the veins in such a manner that they allow the
free passage of the blood upwards, but a backward motion of the blood
would expand the cup-like valves and stop the passage; so that the
blood can only move in one direction, and that _towards the heart_.

922. _How frequently does the total amount of blood circulate through
the system?_

The blood circulates once through the body in about _two minutes_.
If, therefore, we estimate the amount of blood at twenty-four pounds,
it follows that no less than _twelve pounds of blood pass through the
heart every minute_; and it is estimated that if the blood moved with
equal force in a straight line it would pass through _one hundred and
fifty feet in a minute_.




CHAPTER XLV.


923. _How many bones are there in the human body?_

There are _two hundred and forty-six_, and they are apportioned to the
various parts of the body in the following numbers:--

    Head                      8
    Ears                      6
    Face                     14
    Teeth                    32
    Back-bone and its base   26
    Chest, &c.               26
    Arms and Hands           64
    Legs and Feet            62
    Small moveable bones      8

[Verse: "Our bones are scattered at the grave's mouth, as when one
cutteth and cleaveth wood upon the earth."--PSALM CXLI.]

924. _Of what substances are the bones composed?_

One hundred parts of bone consist of

    Cartilage                 32·17 parts
    Blood-vessels              1·13  "
    Carbonate of lime         11·30  "
    Phosphate of lime         51·04  "
    Fluate of lime             2·00  "
    Phosphate of Magnesia      1·16  "
    Soda, chloride of sodium   1·20  "
                             ------
                             100·00

925. _What are the uses of the bones?_

They _protect_ soft and delicate organs; they form a framework to which
the organs are attached, and by which they are _kept in their places_;
and they supply a _mechanism_, by which the _motions of the body are
produced_, in combination with the muscles.

926. _Why is the brain placed within the skull?_

Because that delicate and vital organ, being the _centre and the root
of the nervous system_, requires a position of the _greatest safety_.

927. _Why are the bones that constitute the vertebræ (back-bone)
hollowed out, so as to form a continuous groove?_

Because through that groove the _spinal cord_ passes out from the
brain. Being in the centre of that column of bones, the spinal cord
receives from them a similar protection _to that which the brain
obtains from the skull_.

928. _Why is the head set upon the neck?_

Because in that position it obtains the _freest motion_, can turn
in _any direction_, and is placed relatively to the other parts of
the body, in that situation where it acquires _the greatest possible
advantage_.

929. _Why are the eyes placed in the sockets of the skull?_

Because the bones of the skull _afford protection_ to the delicate and
complicated structure of the eyes, and supply points of attachment, and
grooves, by which the muscles are enabled to _turn the eyes freely_,
and thereby _extend the field of vision_.

[Verse: "Thus saith the Lord God unto these bones, Behold I will
cause breath to enter into you, and ye shall live:"]

930. _Why are the bones of the skull arched?_

Because in that form they acquire _greater strength_, and hence
the utmost degree of safety is combined with extreme _lightness of
material_.

[Illustration: Fig. 54.--VIEW OF THE BONES OF THE THORAX, OR CHEST,
SHOWING THE PROTECTION AFFORDED TO THE ORGANS OF CIRCULATION AND
RESPIRATION.]

     A. The sternum, or breast-bone.

     B B. The _ribs_, which rise a little from behind, and fall as they
     come forward, by which they acquire a greater flexibility.

     C C. The _cartilaginous points_ of the short ribs, by which their
     expansive and compressive powers are much increased.

     D E. Part of the vertebral column, or back-bone.

931. _Why are the bones of the skull divided by sutures (seams), with
points which fit into each other like small teeth?_

Because, by that arrangement, _concussions of the skull_, which might
be fatal to the brain, are _deadened_, and injuries from accident
_greatly modified_.

[Verse: "And I will lay the sinews upon you, and will bring up flesh
upon you, and cover you with skin, and put breath in you, and ye shall
live; and ye shall know that I am the Lord."--EZEKIEL XXXVII.]

932. _Why are the heart, lungs, &c., placed within the chest?_

Because the functions of those organs require _considerable space_,
while their importance in the system of life, renders it essential that
they should be _securely protected_ from the probabilities of accident.

933. _Why are the heart and lungs enclosed for protection in a series
of ribs, and not in a close case, like the brain?_

Because, by the inflation and contraction of the lungs, their _capacity
is constantly changing_. When man takes a moderate inspiration, he
inhales about _thirty cubic inches of air_, and the lungs increase in
size _one-eighteenth of their whole capacity_. Consequently, were they
enclosed in a frame of _fixed dimensions_, it must needs be, to that
extent at least, larger than is necessary, when the frame is made to
dilate and contract with the capacity of the lungs.

So perfect is the Almighty contrivance, that not only are the ribs made
to _protect_ the lungs, but, by their elasticity, and the contractions
and dilations of the muscles which lie between them, they _assist the
lungs in their labours_, and work with them in perfect harmony.

934. _Why are the bones of the arms, legs, &c., made hollow?_

Because _lightness_ is thereby combined with _strength_. There is a
provision by which, in the extremities of bones, where an enlarged
surface is required, _lightness_ is still combined with the necessary
degree of strength.

The bones are made up of a _cellular formation_; and this generally
occurs in parts which are much called into action, in the various
movements of the body.

[Illustration: Fig. 55.--SECTION OF THE KNEE JOINT, SHOWING THE
CELLULAR STRUCTURE OF BONE, BY WHICH LIGHTNESS AND STRENGTH ARE
OBTAINED.]

     A. Lower part of the bone of the thigh.

     B. Head of the bone of the leg.

     C. The knee cap, showing its relation to the other bones, and the
     manner in which it is enclosed by the tendons seen at Fig. 58.

     D. A pad of fat, lessening the friction of the bones, and
     modifying the shocks produced by jumping, &c.

[Verse: "Again he said unto me, Prophesy upon these bones, and say
unto them, O ye dry bones, hear the word of the Lord."--EZEKIEL XXXVII.]

935. _Why are the bones of the arms and legs formed in long shafts?_

Because a considerable _leverage_ is gained, by which the advantages of
_quickness of motion_, and _increase of mechanical power_, are secured.

936. _Why are the bones of the hands and feet numerous and small?_

Because the motions of the hands and feet are very _varied and
complicated_. There are no less than _twenty-eight bones_ in one hand
and wrist; and about _as many_ in a foot and ankle. To these are
fastened a great number of _ligaments and muscles_, by which their
varied compound movements are controlled. But for the complexity of
the mechanism of our hands and feet, our motions would be extremely
awkward, and many of the valuable mechanical inventions which now
benefit mankind, could never have been introduced. The bones of the
hands and feet are in number equal to _one-half of the whole of the
bones of the body_.




CHAPTER XLVI.


937. _What are ligaments?_

Ligaments consist of bands and cords of a _tough_, _fibrous_, _and
smooth substance_, by which the bones are bound together and held in
their places, allowing them freedom to move, and supplying smooth
surfaces over which they glide.

938. _Why are the joints bound with ligaments?_

Because the bones would otherwise be constantly liable to _slip from
their places_.

[Verse: "That which is born of the flesh is flesh; and that which is
born of the Spirit is spirit."--JOHN III.]

939. _What are tendons?_

Tendons are _long cords_, of a substance similar in its nature to
_cartilage_, by which _the muscles are attached to the bones_.

[Illustration: Fig. 56.--SHOWING A BALL AND SOCKET JOINT, AND THE
MANNER IN WHICH LIGAMENTS ARE EMPLOYED TO HOLD BONES IN THEIR
POSITIONS.]

     A. The _ball_, or _head_ of the thigh bone.

     B. The _socket_, showing the ligament in the socket, which holds
     the head of the bone in its place, but allows it free motion.

     C. _Ligaments_ tied from bone to bone, giving firmness to the
     parts.

940. _Why are tendons used to attach the muscles to the bones?_

Because, by this arrangement, the large muscles by which the
extremities are moved, _may be placed at some distance_ from the bones
upon which they act, and thus the extremities, instead of being large
and clumsy, are _small_ and _neat_.

941. _How many muscles are there in the human body?_

There are about _four hundred and forty-six muscles_ that have been
dissected and described, and the actions of which are perfectly
understood. But there is probably a much larger number of muscles, and
of compound actions of muscles, than the skill of man has been able to
recognise.

[Verse: "All flesh is not the same flesh: but there is one kind of
flesh of men, another flesh of beasts, another of fishes, and another
of birds."--CORINTHIANS XVI.]

[Illustration: Fig. 57.--ILLUSTRATION OF THE RELATION OF MUSCLES,
TENDONS, AND BONES.]

942. _What is the constitution of a muscle?_

Every muscle is made up of a number of _parallel fleshy fibres_, or
threads, which are bound together by a smooth and soft tissue, forming
a sheath or case to the muscle, and enabling it to _glide freely_ over
the surfaces upon which it moves.

     A. Lower extremity of the muscle which draws the fore-arm towards
     the upper-arm, bends the elbow, raises the hand to the head, and
     is powerfully exerted in pulling, lifting, &c.

     C. A muscle which gives off four long _tendons_, which pass under
     the _ligaments_ of the wrist, one to each finger, and by which the
     fingers are bent upon the palm of the hand, as in grasping, &c.

     F. _Tendon_ of a muscle which draws the little finger and the
     thumb towards each other.

     The _ligaments_ may be seen enfolding the finger-joints, and also
     crossing the wrist, underneath the _tendons_.

The muscles are compressed into _tendinous cords_ at their ends, by
which they are _united to the bones_.

They are arranged in _pairs_, having reciprocal actions--each muscle
having _a companion muscle_ by which the part which it moves is
restored to its original position, when the influence of the first
muscle is withdrawn, and the stimulus given to bring back the part.

943. _Why can we raise our fingers?_

Because muscles which lie _on the fore-arm_, and have their tendons
fastened at the ends of the fingers, _contract_, and by becoming
shorter, _draw the fingers upward_, and towards the arm.

[Verse: "Thou hast clothed me with skin and flesh, and hast fenced
me with bones and sinews."--JOB XI.]

944. _Why can we throw back the fingers after they have been raised?_

Because the muscles at the back of the arm, _whose tendons are attached
to the back of the fingers_, contract and restore them to their former
position.

945. _What degree of strength do the muscles possess?_

The degree of strength of a muscle depends upon the _healthy condition_
of the muscle, the _amount of stimulus_ which it receives at the time
of exertion, and the manner in which _its powers are applied_.

The great muscle of the calf of the leg has been found, when removed
from a dead body, to be capable of sustaining a weight equal to _seven
times the weight of the entire body_.

_But the contractile power of the living muscles_ is very great: the
thigh bone has frequently been broken by muscular contractions in fits
of epilepsy. And in cases where there has been a dislocation of the
thigh, the head of the thigh-bone being thrown out of its socket, (Fig.
56) it has been found necessary to employ strong ropes, attached to a
wheel turned by several hands, in order to _overcome the contraction of
the excited muscles, and to enable the operator to restore the bone to
its place_.

946. _What is the stimulus which sets the muscles in action?_

The muscles are excited to action by _the nerves_, which they receive
from the _spinal cord_.

947. _Why does it require the influence of the will to set the arms in
motion?_

Because the muscles which form their mechanism are _voluntary_
muscles--that is, they are subject to the _will of man_, and
influenced by impulses directed to them through the nervous system _by
the mind_, which is the governing power.

[Verse: "And he took him by the right hand, and lifted him up; and
immediately his feet and ankle bones received strength."--ACTS III.]

948. _Why does the heart beat without any effort of the will?_

Because the muscles of the heart are _involuntary muscles_--that is,
they are _independent of the will_, and receive _a continuous nervous
stimulus_ which is not _under the controul of the mind._

[Illustration: Fig. 58.--MUSCLES AND VESSELS OF THE LEG AND FOOT.]

     A. A large _ligament_, which covers the knee pan, or moveable bone
     of the knee, by which the ends of the bones of the thigh and leg
     are kept from slipping over each other.

     B. A muscle which passes underneath the cartilages of the ankle,
     and gives off four _tendons_, which are distributed to the toes,
     and by which they are extended in elongating the foot, walking, &c.

     C. Part of the muscle which forms the fleshy bulb of the calf of
     the leg, and which terminates in the large _tendon_ attached to
     the heel, called the _tendon of Achilles._

     D. One of the ligaments which bind the tendons and the bones of
     the ankle.

     E. _Arteries_ proceeding from the large vessel descending the leg,
     by which the toes are supplied.

949. _Why are the muscles of the arms, &c., made subject to the
controul of the will?_

Because, as they supply the mechanism through which we adapt ourselves
to our varying wants and circumstances, it was necessary that they
should be placed under the controul of the mental power, and be moved
_only in accordance with man's necessities._

[Verse: "If thou sayest, Behold, we knew it not; doth not he that
pondereth the heart consider it? and he that keepeth thy soul, doth
not he know it? and shall not he render to every man according to his
works?"--PROVERBS XXIV.]

950. _Why are the motions of the heart, &c., made independent of the
will?_

Because, as the necessity for the heart's motion is _fixed and
unalterable_, the constant motion of the heart could be best secured by
giving it a _fixed nervous influence_, by which it might be unfailingly
prompted to fulfil its functions.

If the movements of man's heart were _subject to his will_, he would
be constantly required to regard the operations of that organ; and so
large an amount of mental care and physical exertion would have to
be employed in that direction, that man's sole work would be to keep
himself alive. Hence we see the goodness of the Creator in _giving_
life to man, and in _keeping the vital impulses under his divine care_.




CHAPTER XLVII.


951. _What are nerves?_

The nerves are branches of the _brain_ and the _spinal cord_; they are
distributed in great numbers to all the active and sensitive parts of
the body.

952. _What is the spinal cord?_

The spinal cord is a long and large cord of nervous matter,
which extends from the brain through a continuous tube formed by
corresponding hollows in the bones of the back. It serves as a nervous
trunk _for the distribution of nerves_, just as the aorta distributes
branches of blood-vessels.

953. _Why is the spinal cord placed in the grooves formed by the
back-bone?_

Being a very vital part of the system, and from the delicacy of
its structure liable to injuries, it is set in the back-bone for
_protection_; and so great is its security that it is only by force of
an unusual kind that it can be injured.

[Verse: "A sound heart is the life of the flesh: but envy is the
rottenness of the bones."--PROVERBS XIV.]

954. _How can branches proceed from it, if it is so securely encased in
bone?_

Because in the bones, on each side of the spinal cord, there are
_smaller grooves_ for the transmission of the nervous branches.

955. _Of what does the nervous system consist?_

Of the _brain_, the _spinal cord_, and the branches which are called
_nerves_.

[Illustration: Fig. 59.--SHOWING THE DISTRIBUTION OF NERVES AND VEINS,
AND ILLUSTRATING THE MANNER IN WHICH THEY PASS THROUGH THE FLESH TO
REACH THE PARTS TO WHICH THEIR FUNCTIONS BELONG.]

     A. B. _Veins_ of the fore-arm.

     B. Canal formed in the muscle, through which a _trunk-vein_
     emerges.

     C. Canal formed in the muscle, through which a large _nerve_
     emerges.

     D. Canal through which a _vein_ enters to communicate with the
     deep muscles of the arm.

956. _What is the constitution of a nerve?_

It consists of a thin membrane, or sheath, surrounding _a greyish oily
matter_, which forms the nervous marrow. In the centre of this marrow
is usually found _a small fibre_, which is supposed to be the essential
part of the nerve; and most nerves consist of a number of these sheaths
enclosing fibres running in parallel directions.

957. _What is the nervous fluid?_

The term _nervous fluid_ is used to express our ideas of the mode by
which the brain and spinal cord influence the remote parts: just as we
say the _electric fluid_, without knowing that such a fluid exists. It
is the most convenient form of expression.

958. _How many classes of nerves are there?_

There are:--

1. The nerves of _motion_.

2. The nerves of _sensation_.

3. The nerves of _special sense_.

4. The nerves of _sympathy_.

[Verse: "Having many things to write unto you, I would not write
with paper and ink; but I trust to come unto you, and speak face to
face, that our joy may be full."--II JOHN.]

959. _What are the nerves of motion?_

The _nerves of motion_ are those which, in obedience to the will,
_stimulate the muscles to act_, and apportion the amount of stimulation
they convey to the degree of exertion required.

[Illustration: Fig. 60.--MUSCLES OF THE HEAD AND FACE, WITH NERVES
DISTRIBUTED THERETO.]

     A A A. The _facial nerve_ emerging from underneath the ear, and
     distributing branches to the cheeks, temple, forehead, &c. This
     nerve excites the muscles of the face, and is chiefly instrumental
     in producing the expressions of the countenance under the changing
     emotions of the mind.

     B B B. _Muscles_ by which various motions are imparted to the
     head, face, mouth, &c., under the _stimulus of the nerves_.

960. _What are the nerves of sensation?_

The _nerves of sensation_ are those which _impart a consciousness to
the brain_ that its commands to the nerves of motion have been obeyed,
and how far they have been fulfilled.

[Verse: "Oh that men would praise the Lord for his goodness, and for
his wonderful works to the children of men."--PSALM CVII.]

     Let us perform a simple experiment, which will more clearly
     illustrate the phenomena of _motion_ and of _sensation_, which we
     are now describing, than a great deal of writing upon the subject.
     You hold in your hand this book: close it, and set it upon the
     table; lay your hands passively upon your lap, and then _will_
     your hand, to take up the book, which is the same as to say,
     _command_ your hand to take up the book. What occurs? The hand,
     immediately obeying your desire, stretches forward to the book,
     and takes hold of it. How do you know that you have hold of it?
     You _see_ that you have: but were your eyes closed, you would be
     equally aware that the hand had reached the book, and fulfilled
     your wishes. It is by the nerves of _sensation_ that you are made
     aware that the hand has fulfilled your instructions.

     Consider what took place in the simple action. In the first
     instance, a desire arose in your mind to take up the book. The
     _brain_ is the organ of the mind; and having branches either
     proceeding from itself, or from the spinal cord, to every part of
     the body--branches that traverse like telegraphic wires throughout
     every part of the system,--it transmitted instructions along the
     nerves that proceed to the muscles of the arm and hand, directing
     them to take up the book. This was done instantly; and as soon
     as it was done you became conscious that your will had been
     obeyed--because _the nerves sent back a sensation to the brain
     acquainting it that the book had been taken up_, and that at the
     moment of the dispatch it was in the firm hold of the hand.

     In all the varied motions of the body this double action of the
     nerves takes place. It is obvious that without an _outward_
     impulse from the brain, upon which the desire of the mind first
     made an impression, no motion of the muscles of the arm and the
     hand could have taken place; and it is also obvious that without
     an _inward_ impulse from the nerves to the brain you would not
     have known that the muscles had fulfilled your instructions. The
     hand might have dropped by the side of the book, or have gone too
     far, or not far enough, and you would not have been aware of the
     result, but for an inward communication through the nerves.

     We are not now speaking of the nerves which endow us with the
     sense of _feeling_, because they are regarded as separate and
     distinct from those nerves that produce in us consciousness
     of muscular response. When we walk, rise, or sit, we are made
     conscious, without any special feeling being exerted, that
     the muscles have placed the limb, or the body, in the desired
     position, that it is set down safely and firmly, and that we may
     repose upon it securely without further attention. We refer the
     impressions made by the book upon the nerves of the hand, and
     which enable us to tell whether it feels hot or cold, whether
     its surface is rough or smooth, and so on, to the special sense
     of _feeling_. The consciousness of muscular action is a separate
     and distinct function; and it is generally believed that the same
     nerves that convey the command of the will outward, bringing back
     the intimation that the will has been obeyed, but that _different
     fibres_ of the nerves convey the _outward_ and the _inward_
     impulses. A single nerve may therefore be likened to a _double
     wire_ connected with the electric telegraph: one transmitting
     despatches in one direction, and the other in the opposite
     direction.

961. _What are the nerves of special sense?_

The nerves of special sense are those through which we _hear_, _see_,
_feel_, _smell_, and _taste_.

[Verse: "For the Lord seeth not as man seeth; for man looketh on the
outward appearance, but the Lord looketh on the heart."--SAMUEL XVI.]

962. _What are the nerves of sympathy?_

The nerves of sympathy, or the system of _sympathetic nerves_, are
those which are distributed to the _internal organs_, and which are
independent of the will. They regulate the motions of the heart, the
lungs, the stomach, &c., and stimulate the organs of secretion, so that
those organs _work in harmony with each other_.

As the internal organs are all more or less dependent upon each other,
and unite their functions for similar ends, it is obvious that there
should prevail among them a _mutual consciousness_ of their state.
Otherwise, when the stomach had formed chyme, the liver might have no
bile ready to fulfil its office; the absorbents might be in a state of
rest at the moment when nutrition was set before them; and the heart
might beat slowly, while the lungs were in active exertion to obtain
additional blood to support an active exercise. The sympathetic system
of nerves therefore _regulates and harmonises these internal functions_.




CHAPTER XLVIII.


963. _Why do we see objects?_

Because the light which is reflected from them enters our eyes and
produces images of their forms upon a membrane of nerves called the
_retina_, just as images are produced upon a mirror.

964. _Why does this enable us to see?_

Because the membrane which receives the images of objects is connected
with the _optic nerve_ which transmits to the brain impressions made by
the reflections of light, just as other nerves convey the effects of
feeling, hearing, tasting, &c.

965. _Why are we enabled to move our eyes?_

Because various muscles are so placed in relation to the eyeball, that
their contraction draws the eye in the direction required. We are thus
enabled to adjust the direction of the eye to the position of the
objects we desire to see, in other words to _set the mirror in such a
position that it will receive the reflection_. (See 517.)

[Verse: "Truly the light is sweet, and a pleasant thing it is for
the eyes to behold the sun."--ECCLESIASTES XI.]

966. _Why are we enabled to see large objects upon so small a surface?_

Because the lenses and humours of the eye _collect the rays of light_
coming from every direction, and, _bringing them into a focus_,
transmit them to the retina, where each ray impresses upon the nervous
surface the qualities it received from the object which reflected it.

[Illustration: Fig. 61.--THE EYEBALL AND ITS MUSCLES.]

     A. Portion of _bone_ through which the optic nerve passes in its
     communication between the brain and the eye.

     B. The _optic nerve_, from before which an _external muscle_ has
     been cut away, leaving its two attachments.

     C. The _globe_ of the eye.

     D. The muscle which turns the eye _outward_, and which is
     counteracted by a muscle on the other side.

     E. The muscle which passes through a loop, or staple of cartilage
     I, and _turns the eye obliquely_. It is counteracted by a muscle
     situated underneath.

     F. The muscle situated underneath, which turns _the eyeball
     upwards_, and is counteracted by

     G. The muscle which _turns the eyeball downwards_.

     H. The muscle attached to a bone which _turns the eyeball upwards_.

     I. The _cartilaginous loop_ through which a muscle passes.

     J. The front chamber of the eye filled with a clear fluid.

     K. Fragment of the bone by which one of the muscles is fastened.

967. _Why do some persons squint?_

Because it sometimes happens that a muscle of the eye _acts too
powerfully_ for its companion muscle, and draws the eye too much on one
side.

968. _Why does the pupil of the eye look black?_

Because the pupil is an _opening_ through which the rays of light pass
into the chamber of the eye. There is, therefore, nothing in the pupil,
of the eye to reflect light.

[Verse: "Keep me as the apple of thine eye; hide me under the shadow
of thy wings."--PSALM XVII.]

969. _Why is the pupil of the eye larger sometimes than at others?_

Because the _iris_, a ring of extremely fine muscles which surround the
pupil, contracts when too much light falls upon the retina, and dilates
when the light is feeble. It therefore enlarges or diminishes the size
of the pupil to _regulate the admission of light_.

[Illustration: Fig. 62.--SECTION OF THE EYE SEEN FROM BEHIND.]

     A. The _pupil_ of the eye through which the light enters.

     B. The _iris_, which dilates or contracts, and thereby increases
     or lessens the size of the _pupil_.

     C. The three coats of the eye, called the _sclerotic_, _choroid_,
     and _retina_.

     D. The _ciliary processes_, or hair-like muscles, which have a
     slight vibratory motion which they impart to the fluids of the eye.

     E. The dark coat of the _choroid_, the coat forming the _retina_
     removed.

970. _Why have we two eyes?_

Because the field of vision is thereby _much extended_; the _intensity_
of sight is also increased, the impressions upon the brain being
clearer and better defined, just as in a _stereoscope_ the effect of
vision is heightened by a double picture; the sense of sight being more
_constantly_ exercised than any other sense during our waking moments,
_one eye is frequently called upon to give rest to the other_; and
the important faculty of vision, being endangered by the necessary
exposure of some parts of the eye, and the equally necessary delicacy
of an organ formed to receive impressions from so ethereal an element
as light, is rendered the more secure to us, since though one eye may
become enfeebled, diseased, or wholly lost, _the other eye will retain
the blessing of sight_.

[Verse: "The eyes of the Lord are upon the righteous, and his ears
are open unto their cry."--PSALM XXXIV.]

971. _Why, having two eyes, and each eye receiving a reflection upon
its retina, does the brain experience only one impression of an object?_

Because, besides those optical laws which bring upon the two retinas
the exactly corresponding images of the same objects, the optic nerves
_meet_ before they reach the brain, _and blend the impulses which they
convey_.

972. _Why are the eyes provided with eyelids?_

Because the eyes require to be _defended_ from floating particles
in the air, and to be kept _moist and clean_. The eyelids form the
shutters of the eye, defending it when waking, by closing upon its
surface whenever danger is apprehended, moistening its surface when it
becomes dry, and covering it securely during the hours of sleep.

973. _Why are the eyelids fringed with eyelashes?_

Because the eyelashes assist to modify the light, and to protect
the eye, without actually closing the eye-ids. When the eyelids are
partially closed, as in very sunny or dusty weather, the eyelashes
cross each other, forming a kind of shady lattice-work, from the
interspaces of which the eye looks out with advantage, and sees
sufficiently for the guidance of the body.

974. _Why are we able to see at long or short distances?_

Because the _crystalline lens_ of the eye is a moveable body, and is
pushed forward, or drawn back by fine muscular fibres, according to the
distances of the objects upon which we look. By these means its _focus_
becomes adjusted.

975. _Why do we wink?_

Because, by the repeated action of winking, _the eye is kept moist and
clean_, and the watery fluid secreted by little glands in the eyelids,
and at the sides of the eye, is spread equally over the surface,
instead of being allowed to accumulate. But the action of winking, or
brightening the eye, is so instantaneous that it does not impede the
sight.

[Verse: "And the eye cannot say unto the hand, I have no need of
thee; nor again the head to the feet, I have no need of you."--CORINTH.
XII.]

976. _Whence are the humours and secretions of the eye derived?_

From the blood, which flows abundantly to the eyes, and is circulated
in capillary vessels that are spread out upon the membranous coats of
the eye-balls.

[Illustration: Fig. 63.--SECTION OF THE EYE.]

     A and B. The _sclerotic_, _choroid_, and _retina_, the three
     layers or coats which form the walls of the globe of the eye, and
     enclose its humours.

     C C. The _iris_.

     D. The front chamber of the eye, filled with watery humour.

     E. The _pupil_, through which the rays of light pass to

     F. The _crystalline lens_.

     G G. The _vitreous humour_ enclosed in cells formed by the
     _hyaloid membrane_.

     H. An _artery_ which supplies blood to the _crystalline lens_, and
     which passes through the centre of the _optic nerve_.

     G. The _optic nerve_, showing the sheath in which the nerve is
     enclosed.

977. _Why do tears form in the eyes?_

Because, under the emotions of the mind, the circulation of blood in
the brain, and in its nearest branches, becomes considerably quickened.
The eyes receive a larger amount of blood, and the secretion of the
lachrymal glands being increased, the fluid overflows, and tears are
formed. The use of tears is probably _to keep the eyes cool during the
excitement of the brain_. They are formed also during _laughing_, but
less frequently.

[Verse: "If the whole body were an eye, where were hearing? if the
whole were hearing, where were smelling?"--CORINTHIANS XII.]

978. _Why do we feel inconvenienced by sudden light?_

Because an excess of light enters the eye before the _iris_ has had
_time to adjust the pupil_ to the amount of light to be received.

979. _Why if we look upon a very bright light, and then turn away, are
we unable to see?_

Because the _iris_ has so reduced the pupil while we were looking at
the bright light, that immediately upon turning to a darker object,
_the pupil is too small_ to admit sufficient rays to enable us to see.

[Illustration: Fig. 64.--CAPILLARY BLOOD-VESSELS OF THE EYE.]

     A A. Capillary veins distributed over the _sclerotic coat_.

     B. One of the trunks of the _optic nerve_.

     C. A _nerve_ communicating with the _ciliary processes_.

     D. A _vein_ running parallel with the nerve to the _ciliary
     processes_.

     E. Side view of the _iris_.

980. _Why do we see better after a short time?_

Because the _iris_ has relaxed and enlarged the pupil, therefore _we
receive more rays of light_ from the comparatively dark object, and are
enabled to see it more clearly.

981. _Why do cats, bats, owls, &c., see in the dark?_

Because their eyes are made highly sensitive to _small quantities of
light_. It is also believed that there are certain properties of light
which affect their eyes, but do not affect ours. In other words, that
there are some rays which are luminous to them which are not luminous
to us. Hence they find _light_ in what we call _darkness_.

[Verse: "He that hath ears to hear, let him hear."--MATTHEW XI.]

982. _Why does the pupil of a cat's eye appear nearly closed by day?_

Because the cat's eye is so sensitive to light that the iris _closes
the pupil almost entirely_ to shut out the too powerful light.




CHAPTER XLIX.


983. _Why do we hear?_

Because the _tympanum_ of the ear _receives impressions from sounds_,
and transmits those impressions to the brain in a similar manner to
that in which the retina of the eye transmits the impressions made upon
it by light.

984. _Why is one part of the ear spread out externally?_

The external ear is a _natural ear-trumpet_, and serves to collect the
vibrations of sound, and to conduct them towards the internal ear.

985. _Why is the ear allowed to project, whilst the eye is carefully
enclosed?_

Because the external ear, being formed of tough cartilaginous
substance, and being very simple in its organisation, is but little
liable to injury.

986. _Why do hairs grow across the entrance of the ears?_

Because they prevent the intrusion of insects, and of particles of
dust, by which otherwise the faculty of hearing would be impaired.

     The insect called the _earwig_ is popularly supposed to be so
     named from its tendency to get into the human ear, and cause pain
     and madness by penetrating to the brain. An earwig, however, is no
     more likely to get into the ear than any other insect whose habit
     it is to penetrate the corollas of flowers; and should an insect
     enter the ear, it could get no further than the _membrane of the
     tympanum_, which spreads all over the auditory passage, just as
     the parchment of a drum spreads over the entire circumference of
     that instrument. The fact is, that the wing of the insect, when
     spread, _resembles the external ear_ in shape. It is similar to
     the wing of the stag beetle (_see_ illustration), and this fancied
     resemblance of the wing of the insect to the ear of man may have
     given rise to the name of _ear-wing_, which became corrupted to
     _earwig_.

[Verse: "Doth not the ear try words? and the mouth taste his
meat."--JOB XII.]

987. _Why is wax secreted at the entrance of the ear?_

Because, by the peculiar resinous property which it possesses, _it
improves the sound-conducting power_ of the auditory canal through
which it prevails.

[Illustration: Fig. 65.--THE STRUCTURE OF THE EAR.]

     A A. Glands which secrete wax in the walls of the tube of the ear.

     B. The membrane of the _tympanum_, or drum of the ear, formed in
     the shape of a funnel.

     C C. Bones which act as a sort of sounding-board to the ear,
     giving strength to the vibrations.

     D. The Eustachian tube, which opens into the root of the mouth,
     and which serves to preserve an equilibrium in the density of the
     air occupying the tubes of the ear.

     E and F. The _labrynth_ of the ear, consisting of folds of
     membraneous tubes, filled with fluid, which serves to undulate
     with the vibrations of the _tympanum_, and thus gives clearness
     and precision to the sounds.

     The _auditory nerves_ are distributed in the tubes above described
     (the _vestibule_ and the _cochlea_ E F), and the nerves receive
     their impressions from the undulations of the fluid.

988. _Why do we sometimes hear singing noises in the ear?_

Because the ear is liable to inflammation from various causes, and
when the blood flows unduly through the vessels of the ear it _produces
a slight sound_.

[Verse: "Apply thine heart unto instruction, and thine ears to the
words of knowledge."--PROVERBS XXIII.]

989. _Why do people become deaf?_

Because the ear may be injured in various ways: the tympanum may be
impaired, the fluid of the ear dried up, or the nerves be pressed upon
by swellings in the surrounding parts. When, therefore, the _mechanism
of hearing_ is impaired, the sense of hearing becomes weakened, or
altogether lost.

990. _Why do persons accustomed to loud noises feel no inconvenience
from them?_

Because the _sensitiveness_ of the nerves of the ear becomes deadened.
They do not convey to the brain such intense impulses when they are
frequently acted upon by loud sounds.

991. _Why do persons engaged in battle often lose their hearing?_

Because the vibrations caused by the sounds of artillery are so violent
that they overpower the mechanism of the ear, and frequently _rupture
the connection of the fine nervous filaments_ with the textures through
which they spread.

     The violent concussions of the air produced by volleys of cannon,
     or by loud peals of thunder, have an overpowering effect upon
     persons nervously constituted, and upon the organ of hearing,
     which is more especially affected. As persons have been struck
     blind by intense light, so others have been deafened by intense
     sounds. In 1697 a butcher's dog was killed by the noise of the
     firing to celebrate the proclamation of peace. Two troops of
     horse were dismounted, and drawn up in a line to fire volleys. At
     the moment of the first volley a large and courageous mastiff,
     belonging to a butcher, was lying asleep before the fire. At
     the noise of the first volley the dog started up, and ran into
     another room, where it hid itself behind a bed; on the firing of
     the second volley, it ran several times bout the room, trembling
     violently; and when the third volley was fired it ran around once
     or twice with great violence, and then dropped down dead, with
     blood flowing from its mouth and nose. Persons who are painfully
     affected by loud noises should put a little wool in their ears
     when such noises are occurring; they will thereby save themselves
     from temporary inconvenience, and probably preserve the sense of
     hearing from permanent injury.

992. _Why do we smell?_

Because minute particles of matter, diffused in the air, come in
contact with the filaments of the _olfactory nerve_, which are
spread out upon the walls of the nostrils, and those nerves transmit
impressions to the brain, constituting what we call the _odour of
substances_.

[Verse: "And the Lord God formed man of the dust of the ground, and
breathed into his nostrils the breath of life; and man became a living
soul."--GENESIS II.]

[Illustration: Fig. 66.--SHOWING THE DISTRIBUTION OF THE NERVOUS
FILAMENTS UPON SENSITIVE MEMBRANES.]

     A. The _olfactory nerve_, distributed in minute branches upon the
     membrane of the nostril.

     B. The _bulb_ of the _olfactory_ nerve.

     C. The _roots_ from which the olfactory nerve originates.

     D E. _Nerves of the palate_, showing the manner in which they are
     passed through the bones of the roof of the mouth.

993. _Why do hairs grow across the passages of the nostrils?_

Because they form a _defence_ against the admission of dust and
insects, which would otherwise frequently irritate the nervous
structure of the nose.

994. _Why are the nostrils directed downwards?_

Because, as odours and effluvia _ascend_, the nose is directed towards
them, and thereby receives the readiest intimation of those bodies
floating in the air which may be pleasurable to the sense, or offensive
to the smell, and injurious to life.

[Verse: "Can that which is unsavoury be eaten without salt? or is
there any taste in the white of an egg?"--JOB VI.]

995. _Why is the nose placed over and near the mouth?_

Because, as one of the chief duties of that organ is to _exercise a
watchfulness_ over the purity of the substances we eat and drink, it is
placed in that position which enables it to discharge that duty with
the greatest readiness.




CHAPTER L.


996. _Why do we taste?_

Because the tongue is endowed with _gustatory_ nerves, having the
function of _taste_ as their _special sense_, just as the _optic_, the
_auditory_, and the _olfactory_ nerves, have their special duties in
the eyes, ears, and nose.

997. _Why do some substances taste sweet, others sour, others salt,
&c.?_

It is believed that the impressions of taste arise from the various
_forms of the atoms of matter_ presented to the nerves of the tongue.

998. _Why do we taste substances most satisfactorily after they have
remained a little while in the mouth?_

Because the nerves of taste are most abundantly distributed to the
under surface of the tongue; and when solid substances have been in
the mouth a little while, they impregnate the saliva of the mouth with
their particles _and come in contact in a fluid solution with the
gustatory nerves_.

999. _Why if we put a nub of sugar to the tip of the tongue has it no
taste?_

Because the gustatory nerves are _not distributed to that part of the
tongue_.

[Verse: "Wine is a mocker, strong drink is raging; and whosoever is
deceived thereby is not wise."--PROVERBS XX.]

1000. _Why, when we draw the tongue in, do we recognise the sweetness
of the sugar?_

Because the dissolved particles of sugar are _brought in contact_ with
the nerves of taste.

1001. _Through what nerves are we made sensible of the contact of sugar
with the tip of the tongue?_

Through the nerves of _feeling_, which are abundantly distributed to
the tongue to guide it in its controul over the mastication of food.

1002. _Why do connoisseurs of wines close their mouths and distend
their chins for a few seconds, when tasting wines?_

Because they thereby bring the wine in contact with the under surface
of the tongue, _in which the gustatory nerves chiefly reside_.

1003. _Why do they also pass the fumes of the wines through their
nostrils?_

Because _flavour_, in its fullest sense, comprehends not only the
_taste_, but the _odour_ of a substance; and, therefore, persons of
experience attend to both requisites.

The various conditions of taste are defined to be:--

1. Where sensations of _touch_ are alone produced, as by glass, ice,
pebbles, &c.

2. Where, in addition to being _felt_ upon the tongue, the substance
excites sensation in the _olfactory nerves_, as by lead, tin, copper,
&c.

3. Where, besides being _felt_, there are peculiar sensations of
_taste_, expressive of the properties of bodies, as salt, sugar,
tartaric acid, &c.

4. Where, besides being _felt_ and _tasted_, there is an _odour_
characteristic of the substance, and essential to the full development
of its flavours, as in cloves, lemon-peel, caraway-seed, and aromatic
substances generally.

1004. _Why do we feel?_

Because there are distributed to various parts of the body fine nervous
filaments, which have for their special duty the transmission to the
brain of impressions made upon them _by contact_ with substances.

[Verse: "The works of the Lord are great, sought out of all them
that have pleasure therein."--PSALM CXI.]

1005. _In what parts of the body does the sense of touch more
especially reside?_

In the points of the fingers and in the tongue. By laying a piece of
paper upon a table, and upon the paper a piece of cloth, on the piece
of cloth a bit of silk, and on the bit of silk a piece of leather, so
that the edge of each would be exposed to the extent of half-an-inch,
it would be possible by the touch to tell when the finger passed
successively over the leather, silk, cloth, or paper, and arrived on
the table.

Those impressions of touch must have been communicated, with their
extremely nice distinctions, to the sensitive nerves that lie
underneath the skin, and must have been transmitted all the way through
the arm to the brain, although the touch itself was so light as
scarcely to be appreciable with regard to the force applied.

A hair lying on the tongue will be plainly perceptible to the touch
of the tongue; and the surface of a broken tooth will often cause the
tongue great annoyance, by the acute perception it imparts of the
roughness of its surface.

The toes are also highly sensitive, though their powers of touch are
seldom fully developed. Persons who have lost their arms, however,
have brought their feet to be almost as sensitive as fingers. Blind
persons increase, by constant exercise, their powers of touch to such a
degree that they are able to read freely by passing their fingers over
embossed printing; and they have been known to distinguish _colours_ by
differences in their grain, quite unappreciable by other persons.

1006. _Why is feeling impaired when the hands are cold?_

Because, as the blood flows slowly to the nerves, they are less capable
of that perception of touch which is their _special sense_. The skin
contracts upon the nervous filaments, and _impairs the contact_ between
them and the bodies which they touch.

1007. _Why do the fingers prick and sting when they again become warm?_

Because, as the warmth expands the cuticle, and the blood begins to
flow more freely through the vessels, _the nerves are made conscious
of the movements of the blood_, and continue to be so until the
circulation is equally restored to all the parts.

[Verse: "In the sweat of thy face shalt thou eat bread, till thou
return to the ground; for out of it thou wast taken: for dust thou art,
and unto dust shalt thou return."--GENESIS III.]

1008. _Why do persons whose legs and arms have been amputated fancy
they feel the toes or fingers of the amputated limb?_

Because the nervous trunk which formerly conveyed impressions from
those extremities remains in the part of the limb attached to the body.
_The mind has been accustomed to refer the impulses received through
that nervous trunk to the extremity where the sensations arose._
And now that the nerve has been cut, the painful sensation caused
thereby is referred to the extremity which the nerve supplied, and the
sufferers for a time appear to _continue to feel the part which they
have lost_.




CHAPTER LI.


1009. _Why do we perspire?_

Because the skin is filled with very _minute pores_, which act as
outlets for a portion of the water of the blood, that serves to
_moisten and cool_ the surface of the body, and to carry away some of
the matter _no longer needed in the system_.

1010. _How is the perspiration formed?_

By very small _glands_, which lie embedded in the skin. It is estimated
that there are about 2,700,000 perspiratory glands distributed over
the surface of the body, and that these glands find outlets for their
secretion through no less than _seven millions of pores_.

1011. _What is insensible perspiration?_

Insensible perspiration is that _transmission of watery particles
through the skin_ which is constantly going on, but which takes place
so gently that it cannot be perceived. It is, however, very important
in its results, as no less than _from twenty to thirty-three ounces of
water may pass imperceptibly through the skin in twenty-four hours_.

1012. _What is sensible perspiration?_

Sensible perspiration is that moisture which exudes upon the skin _in
drops large enough to be perceptible_, when the body is heated by
exercise or other means.

[Verse: "And Elisha sent a message unto him, saying, Go and wash in
Jordan seven times, and thy flesh shall come again to thee, and thou
shalt be clean."--II KINGS V.]

1013. _Why does a sudden change from heat to cold bring on illness?_

Because the effect of cold _arrests the action of the vessels of the
skin_, and suddenly throws upon the internal organs the excretory
labour which the skin should have sustained.

1014. _Why does a chill upon the skin frequently produce inflammation
of the lungs?_

Because the lungs and the skin together discharge the chief proportion
of the watery fluid of the body. _When the skin's action is checked,
the lungs have to throw off a much greater amount of fluid._ The lungs,
therefore, become _over worked_, and inflammatory action sets in.

1015. _Why does cleanliness promote health?_

Because every atom of dirt which lodges upon the surface of the body
serves to clog and check the working of those _minute pores_, by which
much of the fluid of the body is changed and purified.

In the internal parts of the system, the Creator has made ample
provision for cleanliness. Every organ is so constituted that it
cleanses and lubricates itself. Every surface of the inner body is
perfectly clean, and as soft as silk.

Nature leaves to man the care of those surfaces which are under his
immediate observation and controul; and he who, from idleness, or
indifference to nature's laws, is guilty of personal neglect, _opposes
the evident intentions of the Creator_, and must sooner or later pay
the penalty of disobedience.

1016. _Why does exercise promote health?_

Because it _assists all the functions upon which life depend_. It
quickens the circulation, and thereby nourishes every part of the
body, causing the bones to become firm, and the muscles to become full
and healthy. It promotes breathing, by which oxygen is taken into the
system, and carbon thrown off, and thereby it produces a higher degree
of organic life and strength than would otherwise exist. It promotes
perspiration, by which, through the millions of pores of the skin, much
of the fluid of the body is changed and purified. And it induces that
genial and diffused warmth, which is one of the chief conditions of a
high degree of vitality.

[Verse: "Love not sleep lest thou come to poverty: open thine eyes,
and thou shalt be satisfied with bread."--PROV. XX.]

1017. _Why do we feel fatigue?_

Because those organs which stimulate the mechanism of the body to act,
_themselves require rest and repair_. When the brain and nerves arrive
at that state, they make their condition known to the system generally,
by indications which we denominate _fatigue_.

1018. _Why, after rest, do we return invigorated to our labours?_

Because the nervous system has accumulated, during the hours of rest,
a fresh amount of that _vital force_ which we call the nervous fluid,
and by which the various organs of the body are excited to perform the
duties assigned to them.

1019. _What is sleep?_

Sleep is understood to be that state of the body in which _the relation
of the brain to some parts of the body is temporarily suspended_.

There are some parts of the body that _never sleep_: such are the
heart, the lungs, the organs of circulation, and those parts of the
nervous system that direct their operations.

But when sleep overtakes the system, it seems as if the _relations_ of
those parts under the controul of the will were temporarily suspended;
as if, for instance, those nerves which move the arms, the legs, the
eyes, the tongue, &c., were all at once unfastened, just as the strings
of an instrument are relaxed by the turning of a key, or the throwing
down of a bridge over which they were stretched.

     What is meant by the temporary suspension of the relation of the
     brain to some parts of the body, may be thus explained. Notice
     a man when he sits dosing in a chair: at first his head is held
     up, the brain controlling the muscles of the neck, and keeping
     the head erect. But drowsiness comes on, the brain begins to
     withdraw its influence, and the muscles of the neck becoming as
     it were "unstrung," the head drops down upon the breast. But the
     sleep is unsound, and disturbed by surrounding noises. The brain
     is therefore frequently excited to return its influence to the
     muscles, and draw up the head of the sleeper. He gives a sudden
     start, every muscle is tightened in an instant, up goes the head,
     the eyes open, the ears listen, until a feeling of security
     and composure returns; the sleep again deepens, _the nervous
     connection is again withdrawn_, and then down drops the head as
     before.

[Verse: "Yet a little sleep, a little slumber, a little folding of
the hands to sleep: So shall thy poverty come as one that travelleth;
and thy want as an armed man."--PROVERBS XXV.]

1020. _Why do we dream?_

Dreams appear to arise _from the excitement of the brain during those
hours when its connection with the other parts of the living organism
is suspended_. For instance: a man dreams that he is pursued by a
furious animal, and the mind passes through all the excitement of
flying from danger; but the _connection_ between the moving power, and
the machinery of motion being suspended, no motion takes place. The
same impressions upon the brain, when the nerves were "strung" to the
muscles, would have caused a rapid flight, and a vigorous effort to
escape from the apprehended danger.

1021. _Why do suppers, when indigestible substances are eaten, produce
dreaming?_

Probably because, as the digestive organs are oppressed, and those
parts of the nervous system which stimulate the organs of digestion are
_excited by excessive action_, those portions of the brain which are
not immediately employed by the digestive process are disturbed by that
_sympathy_ which is observed to prevail between the relative parts and
functions of the body.

1022. _Why do we yawn?_

Because, as we become weary, the nervous impulses which direct the
respiratory movements are enfeebled. It has been said that those
movements are involuntary, and that the parts engaged in producing them
are not subject to fatigue. But the operation of breathing is, _to some
extent, voluntary_, though when we cease to direct it voluntarily, it
is involuntarily continued by organs which know no fatigue.

When, therefore, we feel weary--still controuling our breathing in our
efforts to move or to speak--there frequently arrives a period when,
for a few seconds, the respiratory process is suspended. It seems to
be the point at which the voluntary nerves of respiration are about to
deliver their office over to the involuntary nerves; but the pause in
the respiration has caused a momentary deficiency of breath, and the
involuntary nerves of respiration, coming suddenly to the aid of the
lungs, cause a spasmodic action of the parts involved, and _a yawn_,
attended by a _deep inspiration to compensate for the cessation of
breathing_, are the result.

[Verse: "And it shall be, when they say unto thee, Wherefore sighed
thou that thou shalt answer, For the tidings, because it cometh; and
every heart shall melt, and all hands shall be feeble."--EZEKIEL XXI.]

1023. _Why do we cough?_

Because the respiratory organs are excited by the presence of some body
foreign or unnatural to them. A cough is an effort on the part of the
air tubes to free themselves from some source of irritation. And so
important are the organs of breathing to the welfare of the body, that
the muscles of the chest, back, and abdomen, _unite in the endeavour to
get rid of the exciting substance_.

1024. _Why do we sneeze?_

Because particles of matter enter the nostrils and excite the nerves
of feeling and of smell. In sneezing, as in coughing, the effort is
to free the parts affected from the intrusion of some matters of an
objectionable nature. And in this case, as in the former one, there is
a very general sympathy of other organs with the part affected, and an
energetic effort to get rid of the evil.

1025. _Why do we sigh?_

The action of sighing arises from very similar causes to those of
yawning. But in sighing, the nervous depression is caused by _grief_;
while in yawning, it is the result of _fatigue_. In sighing, the effect
is generally erased by an _expiration_--in yawning by an _inspiration_.
The mind, wearied and weakened by sorrow, omits for a few seconds to
continue the respiratory process; and then suddenly there comes an
involuntary expiration of the breath, causing a faint sound as it
passes the organs of the voice.

1026. _Why do we laugh?_

Laughing is caused by the very opposite influences that produce
sighing. The nervous system is highly excited by some external cause.
The impression is so intense, and the mind so fixed upon it, that the
respiratory process is irregular, and uncontrolled. Persons excited to
a fit of laughter generally hold their breath until they can hold it no
longer, and then suddenly there is a quick expiration causing eccentric
sounds, the mind being too intently fixed upon the cause of excitement,
_either to moderate the sounds, or to controul the breathing_.

[Verse: "Except ye utter by the tongue words easy to be understood,
how shall it be known what is spoken? for ye shall speak into the
air."--CORINTH. XIV.]

1027. _Why do we hiccough?_

Hiccough is caused by a spasmodic twitching of the diaphragm, a
thin muscular membrane which divides the chest from the abdomen. It
generally arises from sympathy with the stomach; and it is highly
probable that the muscular twitches and jerks are so many efforts on
the part of the diaphragm to _assist the stomach to get rid of some
undigested matter_.

1028. _Why do we snore?_

Snoring is caused by air sweeping through the passages that lead from
the mouth through the nostrils, and which, in our waking moments,
are capable of certain muscular modifications to adapt them to our
breathing. But as in sleeping the nervous controul over them is
withdrawn, they are left to the action of the air which, in sweeping by
them, _sets them in vibration_.

     We have endeavoured, by the employment of the simplest language,
     and by reference to some of the most familiar phenomena of nature,
     to impart to the reader a clear conception of those sublime laws
     which control our being, and afford evidence of the goodness and
     power of that Almighty God to whom we are indebted for the life
     that we enjoy, and the varied and beautiful existences which, to
     the rightly constituted mind, make the earth a vast aggregation of
     interesting objects. We will now, before we pass on to the final
     section of our work, review some of the more important facts that
     have been communicated, and devote a few pages to meditations upon
     the formation of the human body--that wonderful temple of which
     each of us is a tenant.

     We have described man's organisation. What is that organisation
     for? _It is to make use of the elements upon which man exists._
     The lungs make use of the air; the eye makes use of the light;
     the stomach, and the system generally, make use of water; every
     part of the body uses heat; and all parts of the system demand
     food. The hand feeds as constantly as the mouth. The mouth is the
     receptacle of food, by which the body is to be fed; the stomach is
     the kitchen in which food is prepared for the use of the body; and
     the blood-vessels are the canals through which the food is sent to
     those members of the body that are in need of it. When we speak
     of man's "organs" or "members," we speak of those parts of the
     living machinery by which the elements are used up, or employed,
     for man's benefit. And this view of the subject, bearing in mind
     that the body is held together as the temple of a living Spirit,
     superior to mere flesh and blood, gives us a higher and clearer
     perception of the distinction between the body and the soul than
     that which we might otherwise entertain. The body is a machine,
     working for the spirit, which is its owner. While the machine
     works, the spirit directs and influences its actions. But when the
     machine stops, the spirit resigns its power over a ruined temple,
     quits it, and flies to a region where, as a spirit, it becomes
     subject to a new order of existence consistent with its severance
     from earthly things and laws, and there it enters upon its eternal
     destiny, according to the judgments and appointments of God. It is
     no longer dependent upon a relation between spiritual and material
     laws.

[Verse: "Not unto us, O Lord, not unto us, but unto thy name give
glory, for thy mercy, and for thy truth's sake."--PSALM CXV.]

     Suppose that the air which man breathes, instead of returning
     from his lungs clear and imperceptible to sight, were tinged with
     colour; we should see, that every time a man breathed, the air
     would rush in a stream into his mouth, and then return again;
     and the air which returned would, being warm, be lighter than
     the outer air, and would rise upward over the man's head, where,
     cooling and mingling with the outer air, it would descend again.
     We do, in fact, see this action evidenced; when in winter time the
     cold condenses the vapour of the breath, we see the little cloud
     constantly rising before the breather's face, and dispersing in
     the surrounding air.

     Is it not a wonderful thing that that clear and elastic substance,
     which you cannot feel, though it touches every part of your body,
     and which you cannot see, is composed of two distinct bodies,
     having very different properties; and that the two bodies can
     easily be separated from each other?

     Air is of the first importance to life. Hence it is provided
     for us everywhere. We require air every second, water every few
     hours, and food at intervals considerably apart. Air is therefore
     provided for us everywhere. Whether we stand or sit; whether we
     dwell in a valley or upon a mountain; whether we go into the
     cellar under our house, or into the garret at the top of it, air
     is there provided for us. God, who made it a law that man should
     breathe to live, also sent him air abundantly, that he might
     comply with that law. And all that is required from man in this
     respect is, that he will not shut out God's bounty, but receive it
     freely.

     As we have employed the idea that if the air were coloured we
     should have the opportunity of marking the process of breathing,
     let us enlarge upon this, and suppose that every time the air were
     returned from the lungs it became of a darker colour, the darkness
     denoting increasing impurity. If we placed a man in a room full
     of pure air, we should see the air enter his lungs, and sent back
     slightly tinged; but this would disperse itself with the other
     air of the room and scarcely be perceptible. As the man continued
     to breathe, however, each measure of air returning from the lungs
     would serve to pollute that abiding in the room, until at last the
     whole mass would become cloudy and discoloured, and we should see
     such a change as occurs when water is turned from a pure and clear
     state into a muddy condition. The air does become polluted with
     each respiration, and although it is colourless, it is as impure
     as if with every breath given off from the lungs it became of a
     dark colour in proportion to its impurity.

     Thus we see how important it is that we should provide ourselves
     with pure air; and that, in seeking warmth and comfort in
     our houses, we should provide an adequate supply of fresh
     atmosphere--because it is more vital to life than either water or
     food.

     Indeed, so constant is our requirement of air, that _if we had
     to fetch it, for purposes of breathing, or simply to raise it
     to our mouths, as we do water when we drink, it would be the
     sole occupation of our lives_--_we could do nothing else_. For
     this reason, God has sent the air to us, and not required us to
     go to the air. And the great error of man is, that in too many
     instances, he shuts off the supply from himself, and brings on
     disease and pain by inhaling a poisonous compound, instead of air
     of a healthful kind, which bears an adaptation to the wants of
     life.

[Verse: "There is a natural body, and there is a spiritual body."--I
CORINTHIANS XV.]

     Whilst the rooms of our house are filled with air, it is otherwise
     with water, which we require in less degree than air. If we have
     not the artificial means by which water is brought to our houses,
     through the pipes of a water company, there is a spring or a pump
     in the garden; or in the absence of these, a good sound cask,
     standing at the end of our house, forming a receptacle to the
     water-pipes that surround it, provides us with a supply of water
     distilled from the clouds. If we were to drink a good draught of
     water once a day, that would be sufficient for all the purposes
     of life, as far as regards the alimentary uses of water. Man is,
     therefore, allowed to go to the stream for his drink, and is
     required to raise it to his lips at those moments when he uses it.

     Although, in breathing, man separates the _oxygen_ of the air from
     the _nitrogen_ thereof, he does not separate the _oxygen_ of the
     water from the _hydrogen_. Water, in fact, undergoes no change
     in the body, excepting that of admixture with the substances of
     the body. And its uses are, to moisten, to cool, to cleanse, and
     also to nourish the parts with which it comes in contact. But it
     affords no nourishment of itself; it mixes with the blood, of
     which it forms a material part, and is the means of conveying _the
     nourishment of the blood_ to every part of the system. After it
     has filled this office, and taken up impurities that are required
     to be removed, it is cast out of the system again, without
     undergoing any chemical change.

     Man's body is to his Soul, in many respects, what a house is to
     its occupant. But how superior is the dwelling which God erected,
     to that which man has built. Reader, come out of yourself, and in
     imagination realise the abstraction of the Soul from the body.
     Make an effort of thought, and do not relinquish that effort,
     until you fancy that you see your image seated on a chair before
     you. And now proceed to ask yourself certain questions respecting
     your bodily tenement--questions which, perchance, have never
     occurred to you before; but which will impress themselves the more
     forcibly upon you, in proportion as you realise for a moment the
     idea of your Soul examining the body which it inhabits. There sits
     before you a form of exquisite proportions, with reference to the
     mode of life it has to pursue--the wants of the Soul for which it
     has to care, and which it has to guard, under the direction of
     that Soul, its owner and master.

     Over the brows that mark the intellectual front of that due
     form, there fall the auburn locks of youth, or the grey hair of
     venerable age. Each of those hairs is curiously organised. If you
     take a branch of a tree, and cut it across, you will find curious
     markings caused by vessels of various structure, all necessary to
     the existence of the plant. In the centre will be found either
     a hollow tube, or a space occupied by a soft substance called
     pith. Each hair of your head is as curiously formed as the branch
     of a tree, and in a manner not dissimilar, though its parts
     are so minute that the unaided eye cannot discern them. Every
     hair has a root, just as a tree has, and through this root it
     receives its nourishment. As the vessel which feed a plant are
     always proportionate to the size of the plant itself, how fine
     must be those vessels which form the roots of the hair, being in
     proportion to the size of the hair, which is in itself so small
     that the eye cannot see its structure? The hair is, in fact, an
     animal plant, growing upon the body in much the same manner that
     plants grow upon the surface of the earth. But how does this hair
     grow? Not alone by the addition of matter at its roots, pushing up
     and elongating its stem: nourishment passes up through its whole
     length, and is deposited upon its end, just as the nourishment of
     a tree is deposited upon its extreme branches. If, after having
     your hair cut, you were to examine its ends by the microscope, you
     would discover the abrupt termination left by the scissors. But
     allow the hair to grow, and then examine it, and you will discover
     that it grows from its point which, in comparison with its former
     state, is perfect and fine. The reason why the beard is so hard
     is, that the ends of the hair are continually being shaved off.
     The hair of the beard, if allowed to grow, would become almost as
     soft as the hair of the head.

[Verse: "The very hairs of your head are all numbered."--MATTHEW XI.]

     But why is man's head thus covered with hair? For precisely the
     same reason that a house is thatched--to keep the inmates warm.
     We might add, also, to give beauty to the edifice. But as beauty
     is a conventional quality--and if men were without it they would
     consider themselves quite as handsome as they do now--we will not
     enlarge upon the argument. Our bald-headed friends, too, might
     have reason to complain of such a partial hypothesis. The brain
     is the great organ upon which the health, the welfare, and the
     happiness of the system depends. The skull, therefore, may be
     regarded as analogous to the "strong box," the iron chest in which
     the merchant keeps his treasure. There is no point at which the
     brain can be touched to its injury, without first doing violence
     to the skull. Even the spinal cord runs down the back through a
     tunnel or tube, formed in a number of strong bones, so closely
     and firmly jointed together, that they are commonly termed "the
     back-bone."

     Look at the eyebrows. What purpose do they fulfil? Precisely that
     of a shed, or arch placed over a window to shelter it from rain.
     But for the eyebrows the perspiration would frequently run from
     the brow into the eyes, and obscure the sight; a man walking in a
     shower of rain would scarcely be able to see; and a mariner in a
     storm would find a double difficulty in braving the tempest.

     Now we come to the eye, which is the window of the Soul's abode.
     And what a window! how curiously constructed! how wisely guarded!
     In the eyelashes, as well as the eyebrows, we see the hair
     fulfilling a useful purpose, differing from any already described.
     The eyelashes serve to keep cold winds, dust, and too bright
     sun, from injuring or entering the windows of the body. When we
     walk against the east wind, we bring the tips of our eyelashes
     together, and in that way exclude the cold air from the surface
     of the eye; and in the same manner we exclude the dust and modify
     the light. The eyelashes, therefore, are like so many sentries,
     constantly moving to and fro, protecting a most important organ
     from injury. The eyelids are the shutters by which the windows
     are opened and closed. But they also cleanse the eye, keeping it
     bright and moist. There are, moreover, in the lids of each eye
     or window, little glands, or springs, by which a clear fluid is
     formed and supplied for cleansing the eye. The eye is placed in a
     socket of the skull, in which it has free motion, turning right
     or left, up or down, to serve the purpose of the inhabitant of
     the dwelling. Of the structure of the eye itself we will not say
     much, for the engravings will afford a clearer understanding than
     a lengthy written description. But we would have you examine the
     formation of the iris of the living eye, the ring which surrounds
     the pupil. Hold a light to it, and you will find that the iris
     will contract and diminish the pupil; withdraw the light, and the
     iris will relax, and the pupil expand, thus regulating the amount
     of light. The images of external objects are formed upon the
     retina of the eye, a thin membrane, spread out upon the extremity
     of a large nerve, which proceeds immediately to the brain, and
     forms the telegraphic cord by which information is given to the
     mind, of everything visible going on within the range of sight.

[Verse: "Thou art of purer eyes than to behold evil, and canst not
look on iniquity."--HABAKKUK I.]

     Now, think for a few moments upon the wonderful structure of those
     windows of the body. Can you fancy, in the walls of your house, a
     window which protects itself, cleanses itself, and turns in any
     direction at the mere will of the tenant; and when that tenant is
     oppressed by excess of light, draws its own curtain, and gives
     him ease; and when he falls asleep, closes its own shutters, and
     protects itself from the cold and dust of night, and the instant
     he awakes in the morning, opens, cleanses itself with a fluid
     which it has prepared during the night, and kept in readiness; and
     repeats this routine of duty day after day for half a century,
     without becoming impaired? Such, nevertheless, is the wonderful
     structure of the window of the body--the eye.

     In some scientific works that have recently been published,
     curious investigations have been made known. It has been shown
     that the eye is impressed momentarily, as a photographic plate
     is impressed by the rays of the sun. But the photography of the
     eye has this extraordinary quality--that one image passes away,
     and another takes its place immediately, without confusion or
     indistinctness. But the most wonderful assertion of all is, that
     under the excitement of memory these photographic images are
     restored; and that when, "in our mind's eye," we see the image
     of some dear departed friend, the retina really revives an image
     which once fell upon its sensitive surface, and which image has
     been stored up for many years in the sacred portfolio of its
     affections!

     Another extraordinary assertion is one which comes supported by
     a degree of authenticity that entitles it to consideration. It
     is said that the eye of a dead man retains an impression of the
     last picture that fell upon the faithful retina. Dr. Sandford, of
     America, examined the eye of a man named Beardley, who had been
     murdered at Auburn, and he published in the _Boston Atlas_ the
     following statement:--"At first we suggested the saturation of the
     eye in a weak solution of atrophine, which evidently produced an
     enlarged state of the pupil. On observing this, we touched the end
     of the optic nerve with the extract, when the eye instantly became
     protuberant. We now applied a powerful lens, and discovered in the
     pupil, the rude, worn-away figure of a man, with a light coat,
     beside whom was a round stone, standing or suspended in the air,
     with a small handle, stuck in the earth. The remainder was debris,
     evidently lost from the destruction of the optic nerve, and its
     separation from the mother brain. Had we performed the operation
     when the eye was entire in the socket, with all its powerful
     connection with the brain, there is not the least doubt but that
     we should have detected the last idea and impression made on the
     mind and eye of the unfortunate man. The picture would evidently
     be entire; and perhaps we should have had the contour, or better
     still, the exact figure of the murderer. The last impression on
     the brain before death is always more terrible from fear than any
     other cause, and figures impressed on the pupil more distinct,
     which we attribute to the largeness of the optic nerve, and its
     free communication with the brain." Whether the supposition, which
     seems to be supported by the experiment above detailed, be correct
     or not, it is in no sense more wonderful than the facts which are
     already known respecting this curious and perfect organ.

[Verse: "Be not rash with thy mouth, and let not thine heart be
hasty to utter anything before God: for God is in heaven, and thou upon
earth; therefore let thy words be few."--ECCLESIASTES V.]

     The nose is given us for two purposes--to enable us to respire and
     to smell. As odours arise from the surface of the earth, the cup
     or funnel of the nose is turned down to meet them. In the nostrils
     hair again serves a useful purpose. It not only warms the air
     which enters the nostrils, but it springs out from all sides, and
     forms an intersecting net, closing the nostrils against dust, and
     the intrusion of small insects. If by any means, as when taking
     a sharp sniff, foreign matters enter the nostrils, the nose is
     armed with a set of nerves which communicate the fact to certain
     muscles, and the organs of respiration unite with those muscles to
     expel the intruding substances. In this action, the diaphragm, or
     the muscle which divides the abdomen from the chest, is pressed
     down, the lungs are filled with air, the passage by which that
     air would otherwise escape through the mouth, is closed up, and
     then, all at once, with considerable force, the air is pressed
     through the nostrils, to free them from the annoying substance. So
     great is the force with which this action takes place, that the
     passage into the mouth is generally pushed open occasioning the
     person in whom the action takes place, to cry "'tsha!" and thus
     is formed what is termed a sneeze. As with the eye, so with the
     nose--innumerable nerves are distributed over the lining membrane,
     and these nerves are connected with larger nerves passing to the
     brain, through which everything relating to the sense of smell is
     communicated.

     The nose acts like a custom-house officer to the system. It is
     highly sensitive to the odour of most poisonous substances. It
     readily detects hemlock, henbane, monk's hood, and the plants
     containing prussic acid. It recognises the foeted smell of
     drains, and warns us not to breathe the polluted air. The nose
     is so sensitive, that air containing a 200,000th part of bromine
     vapour will instantly be detected by it. It will recognise the
     1,300,000th part of a grain of otto of roses, or the 13,000,000th
     part of a grain of musk! It tells us in the mornings that our
     bed-rooms are impure; it catches the first fragrance of the
     morning air, and conveys to us the invitation of the flowers to go
     forth into the fields, and inhale their sweet breath. To be "led
     by the nose," has hitherto been used as a phrase of reproach. But
     to have a good nose, and to follow its guidance, is one of the
     safest and shortest ways to the enjoyment of health.

     The mouth answers the fourfold purpose of the organ of taste,
     of sound, of mastication, and of breathing. In all of these
     operations, except in breathing, the various parts of the mouth
     are engaged. In eating we use the lips, the tongue, and the teeth.
     The teeth serve the purpose of grinding the food, the tongue
     turns it during the process of grinding, and delivers it up to
     the throat for the purposes of the stomach, when sufficiently
     masticated. The lips serve to confine the food in the mouth, and
     assist in swallowing it, and there are glands underneath the
     tongue, and in the sides of the mouth, which pour in a fluid
     to moisten the food. And so watchful are those glands of their
     duty, that the mere imagination frequently causes them to act.
     Their fluid is required to modify the intensity of different
     flavours and condiments in which man, with his love of eating,
     will indulge. Thus, when we eat anything very acid, as a lemon, or
     anything very irritating, as Cayenne pepper, the effect thereof
     upon the sensitive nerves of the tongue is greatly modified by a
     free flow of saliva into the mouth. And if we merely fancy the
     taste of any such things, those glands are so watchful, that they
     will immediately pour out their fluid to mitigate the supposed
     effect.

[Verse: "I say unto you, Swear not at all; neither by heaven, for it
is God's throne; Nor by the earth; for it is his footstool."--MATTHEW
V.]

     In speaking, we use the lips, the teeth, the tongue; and the
     chest supplies air, which, being controlled in its emission, by
     a delicate apparatus at the mouth of the wind-pipe, causes the
     various sounds which we have arranged into speech, and by which,
     under certain laws, we are enabled to understand each other's
     wants, participate in each other's emotions, express our loves,
     our hopes, our fears, and glean those facts, the accumulation of
     which constitutes knowledge, enhances the happiness of man, and
     elevates him, in its ultimate results above the lower creatures to
     which the blessing of speech is denied.

     The curious structure of the tongue, and the organs of speech,
     would fill a very interesting volume. The tongue is unfortunately
     much abused, not only by those who utter foul words, and convert
     the blessing of speech, which should improve and refine, into
     a source of wicked and profane language; but it constantly
     remonstrates against the abuse of food, and the use of things
     which are not only unnecessary for the good of our bodies, but
     prejudicial to their health. When the body is sufficiently fed,
     the tongue ceases its relish, and derives no more satisfaction
     from eating: but man contrives a variety of inventions to whip the
     tongue up to an unnatural performance of its duty, and thus we not
     only over-eat, but eat things that have no more business in our
     stomachs, than have the stones that we walk upon. Can we wonder,
     then, that disease is so prevalent, and that death calls for many
     of us so soon.

     That wonderful essence, the Soul of man, rises above all finite
     knowledge. Its wonders and powers will never, probably, be
     understood until when, in a future state of existence, the
     grandest of all mysteries shall be explained. When we talk of the
     brain, we speak of that which it is easy to comprehend as the
     organ, or the seat of the mind; when we speak of the mind, we
     have greater difficulty in comprehending the meaning of the term
     we employ; but when we speak of the Soul, we have reached a point
     which defies our understanding, because our knowledge is limited.
     The brain may be injured by a blow; the mind may be pained by a
     disagreeable sight, or offended by a harsh word; but the Soul
     can only be influenced secondarily through the mind, which is
     primarily affected by the organs of the material senses. Thus the
     happiness or the misery of the Soul depends to a very great extent
     upon the proper fulfilment of the duties of the senses, which are
     the servants of the Soul, over which the mind presides, as the
     steward who mediates between the employer and the employed.

     The Ear, which is taught to delight in sweet sounds, and in pure
     language, is a better servant of the master Soul, than one which
     delights not in music, and which listens, with approbation or
     indifference, to the oaths of the profane. The Eye which rejoices
     in the beauties of nature, and in scenes of domestic happiness
     and love, is a more faithful servant than one that delights in
     witnessing scenes of revelry, dissipation, and strife. The Nose
     which esteems the sweet odour of flowers, or the life-giving
     freshness of the pure air, is more dutiful to his master than one
     that rejects not the polluted atmosphere of neglected dwellings.
     The Mouth which thirsts for morbid gratification of taste, is more
     worthless than one which is contented with wholesome viands, and
     ruled by the proper instincts of its duty. Who that can understand
     the wonderful structure of the tongue, and the complicated
     mechanism of the organs of speech and of hearing, could be found
     to take pleasure in the utterance of oaths, and of words of vulgar
     meaning? Were those beautiful cords that like threads of silk are
     woven into the muscular texture of the mouth, and along which
     the essence of life travels with the quickness of thought, to do
     the bidding of the will--were they given for no higher use than
     to sin against the God who gave them, and upon whose mercy their
     existence every moment depends?

[Verse: "Out of the same mouth proceedeth blessing and cursing. My
brethren, these things ought not so to be."--JAMES III.]

     The actions of the senses must necessarily affect the mind, which
     is the head steward of the Soul; and the Soul becomes rich in
     goodness, or poor in sin, in proportion as the stewardship, held
     by his many servants, is rightly or wrong-fully fulfilled. As in
     an establishment where the servants are not properly directed
     and ruled, they often gain the ascendancy, and the master has no
     power over them, so with man, when he gives himself up to sensual
     indulgences. The Soul becomes the slave of the senses--the master
     is controlled by the servants.

     With regard to the mechanism of motion, let us take the case of
     a man who is walking a crowded thoroughfare, and we shall see
     how active are all the servants of the Soul, under the influence
     of the mind. He walks along in a given direction. But for the
     act of volition in the mind, not a muscle would stir. The eye
     is watching his footsteps. There is a stone in his path, the
     eye informs the mind, the mind communicates with the brain, and
     the nerves stimulate the muscles of the leg to lift the foot a
     little higher, or turn it on one side, and the stone is avoided.
     The eye alights on a familiar face, and the mind remembers that
     the eye has seen that face before. The man goes on thinking of
     the circumstance under which he saw that person, and partially
     forgets his walk, and the direction of his steps. But the nerves
     of volition and motion unite to keep the muscles up to their work,
     and he walks on without having occasion to think continually,
     "I must continue walking." He has not to make an effort to lift
     his leg along between each interval of meditation; he walks and
     meditates the while. Presently a danger approaches him from
     behind. The eye sees it not--knows no more, in fact, than if it
     were dead. But the ear sounds the alarm, tells the man, by the
     rumbling of a wheel, and the tramp of horses' feet, that he is in
     danger; and then the nerves, putting forth their utmost strength,
     whip the muscles up to the quick performance of their duty; the
     man steps out of the way of danger, and is saved. He draws near
     to a sewer, which is vomiting forth its poisonous exhalations.
     The eye is again unconscious--it cannot see the poison lurking in
     the air. The ear, too, is helpless; it cannot bear witness to the
     presence of that enemy to life. But the nose detects the noxious
     agent, and then the eye points out the direction of the sewer, and
     guides his footsteps to a path where he may escape the injurious
     consequences. A clock strikes, the ear informs him that it is the
     hour of an appointment; the nerves stimulate the muscles again,
     and he is hastened onward. He does not know the residence of his
     friend, but his tongue asks for him, and his ear makes known the
     reply. He reaches the spot--sits--rests. The action of the muscles
     is stayed; the nerves are for a time at rest. The blood which
     had flown freely to feed the muscles while they were working,
     goes more steadily through the arteries and veins, and the lungs,
     which had been purifying the blood in its course, partake of the
     temporary rest.

[Verse: "I am but a little child: I know not how to go out or come
in."--I KINGS III.]

     Let us remember that there are two sets of muscles, acting in
     unison with each other, to produce the various motions; they are
     known by the general terms of _flexors_ and _extensors_; the first
     enable us to bend the limbs, the other to bring the limbs back to
     their former position. The flexors enable us to close the hand,
     the extensors to open it again. The flexors enable us to raise the
     foot from the ground; the extensors set the foot down again in the
     place desired. Consider for a moment the nicety with which the
     powers of these muscles must be balanced, and the harmony which
     must subsist between them in their various operations. When we
     are closing the hand, if the extensor muscles did not gradually
     yield to the flexors--if they gave up their hold all at once, the
     hand, instead of closing with gentleness and ease, would be jerked
     together in a sudden and most uncomfortable manner. If, in such
     a case, you were to lay your hand with its back upon the table,
     and wish to close the hand, the fingers would fall down upon the
     palm suddenly, like the lid of a box. Again, consider how awkward
     it would be in such a case; our walk through the streets would
     become a series of jumps and jerks; when a man had raised his
     foot, after it had been jerked up, there it would stand fixed for
     a second before the opposite muscles could put on their power to
     draw it down again. This case is not at all suppositious: there is
     a derangement frequently observed in horses, in which one set of
     muscles becomes injured, and we may see horses suffering from this
     ailment, trotting along with one of their legs jerking up much
     higher than the others, and set down again with difficulty, just
     in the manner described.

     It is also to be observed that very nice proportions must exist
     between the sizes of the muscles and the sizes of the bones. If
     this were not the case, our motions, instead of being firm and
     steady, would be all shaky and uncertain. In old persons the
     muscles become weak and relaxed; hence there is a tendency in the
     movements of the aged to fall, as it were, together; the head is
     no longer erect, the body bends, the knees totter, and the arms
     lean towards the body as for support.

     In the child a somewhat similar state of things exists. The
     muscles have not been properly developed, nor have they been
     brought sufficiently under the controul of the nervous system. The
     child, therefore, totters and tumbles about, and it is not until
     it has stumbled and tumbled some hundreds of times in its little
     history, that the muscles have become strong enough to fulfil
     their office, or have been brought sufficiently under the controul
     of the nervous system, to perform well the various duties required
     from them.

     In all these things, we recognise the perfection of the divine
     works. We are apt, too apt, to overlook this perfection,
     because it prevails in everything; but by speculating upon what
     inconveniences we might suffer, were not things ordained as they
     are, we obtain most convincing evidences of divine goodness and
     wisdom.

[Verse: "Watchman, what of the night? The watchman said, The morning
cometh, and also the night; if ye will enquire, enquire ye; return,
come."--ISAIAH XXI.]

     Having taken this view of the muscular system of the external
     man, let us turn our attention to the muscles of the internal
     organs. The muscles of which we have been speaking are called
     the voluntary muscles, because we have them under our own
     controul--they are subject to the influences of our will. But
     there is the other set of muscles. What are they? We talk of the
     beating, or of the palpitation, of the heart. But, what is it
     that causes the heart to beat? You cannot, if you wish it, make
     your heart beat more quickly or more slowly. Place your finger
     upon your pulse, and notice the degree of rapidity with which its
     pulsations follow. Now think that you should like to double the
     frequency of those pulsations. Say to the heart, with your inner
     voice, that you wish it to beat 120 times in a minute, instead of
     60. It does not obey you; it does not appreciate your command.
     Now place your finger on the table, and your watch by the side of
     your hand, and tell your finger to beat 60 times in the minute,
     or 100 times, or 150 times, or 200 times, and the finger will
     obey you--because it is _moved by muscles which are subject to
     the will_, while the heart is composed of muscles which are _not
     subject to the will_. Why should this be? Why should man have the
     power to regulate his finger, and not to regulate his heart?

     For the sustentation of our bodies it is needful that the blood
     should ever be in circulation. If the heart were to cease beating
     only for three or four minutes (perhaps less) life would be
     extinct. In this short time the whole framework of man, beautiful
     in its proportions, perfect in its parts, would pass into the
     state of dead matter, and would simply wait the decay that follows
     death. The eye would become dull and glazed, the lips would turn
     blue, the skin would acquire the coldness of clay--love, hope,
     joy, would all cease. The sweetest, the fondest ties would be
     broken. Flowers might bloom, and yield their fragrance, but
     they would be neither seen nor smelt; the sun might rise in its
     brightest splendour, yet the eye would not be sensitive to its
     rays; the rosy-cheeked child might climb the paternal knee; but
     there, stiff, cold, without joy, or pain, or emotion of any kind,
     unconscious as a block of marble, would sit the man _whose heart
     for a few moments had ceased to beat_.

     How wise, then, and how good of God, that he has not placed
     this vital organ under our own care! How sudden would be our
     bereavements--how frequent our deaths, how sleepless our nights,
     and how anxious our days, if we had to keep our own hearts at
     work, and death the penalty of neglect.

     And yet, before we were born, until we reach life's latest
     moment--through days of toil, and nights of rest--even in the
     moments of our deepest sin against the God who at the time is
     sustaining us, our hearts beat on, never stopping, never wearying,
     never asking rest.

     This brings us to another reflection. Our arms get weary, our
     legs falter from fatigue, the mind itself becomes overtaxed,
     and all our senses fall to sleep. The eye sees not, the ear is
     deaf to sound, the sentinels that surround the body, the nerves
     of touch, are all asleep--you may place your hand upon the brow
     of the sleeping man, and he feels it not. Yet, unseen, unheard,
     without perceptible motion, or the slightest jar to mar the rest
     of the sleeper, the heart beats on, and on, and on. As his sleep
     deepens, the heart slackens its speed, that his rest may be the
     more sound. He has slept for eight hours, and the time approaches
     for his awakening. But is the heart weary--that heart which has
     toiled through the long and sluggard night? No! The moment the
     waking sleeper moves his arm, the heart is aware that a motion has
     been made, that effort and exercise are about to begin. The nerves
     are all arousing to action; the eyes turn in their sockets, the
     head moves upon the neck; the sleeper leaves his couch, and the
     legs are once more called upon to bear the weight of the body.
     Blood is the food of the eye, the food of the ear, of the foot,
     the hand, and every member of the frame. While they labour they
     must be fed--that is the condition of their life, the source of
     their strength. The heart, therefore, so far from seeking rest, is
     all fresh and vigorous for the labours of the day, and proceeds to
     discharge its duty so willingly, that we do not even know of the
     movements that are going on within us.

[Verse: "Awake up, my glory; awake, psaltery and harp: I myself will
awake early."--PSALM LVII.]

     Thus we have seen the difference between the voluntary and the
     involuntary muscles, and we have perceived the goodness of our
     Creator in not entrusting to our keeping the controul of an organ
     so vital to life, as the heart.

     But the heart is not the only organ which thus works unseen and
     unfelt. There are the lungs and the muscles of the chest, the
     stomach, and other parts occupying the abdomen, together with all
     those muscular filaments which enter into the structure of the
     coats and valves of the blood-vessels, and which assist to propel
     the blood through the system. All these are at work at every
     moment of man's life; and yet, so perfect is this complicated
     machinery, that we really do not know, except by theory, what is
     going on within us.

     During the time that the sleeper has been at rest, the stomach has
     been at work digesting the food which was last eaten. Then the
     stomach has passed the macerated food into the alimentary canal,
     the liver has poured out its secretion, and produced certain
     changes in the condition of the dissolved food: and the lacteals,
     of which there may be many thousands, perhaps millions, have been
     busy sucking up those portions of the food which they knew to be
     useful to the system, whilst they have rejected all those useless
     and noxious matters upon which the liver, like an officer of
     health, had set his mark, as unfitting for the public use. This
     busy life has gone on uninterruptedly; every member of that body,
     every worker in that wonderful factory, has been unremitting in
     his duty, and yet the owner, the master, has been asleep, and
     wakes up finding every bodily want supplied!

     Notwithstanding that much has already been said of the wonders
     that pertain to the eye, it has not yet been considered as the
     seat of _tears_, those mute but eloquent utterers of the sorrows
     of the heart. Beautiful Tear! whether lingering upon the brink
     of the eyelid, or darting down the furrows of the care-worn
     cheek--thou art sublime in thy simplicity--great, because of thy
     modesty--strong, from thy very weakness. Offspring of sorrow! who
     will not own thy claim to sympathy? who can resist thy eloquence?
     who can deny mercy when thou pleadest?

     Every tear represents some in-dwelling sorrow preying upon the
     mind and destroying its peace. The tear comes forth to declare the
     inward struggle, and to plead a truce against further strife. How
     meet that the eye should be the seat of tears--where they cannot
     occur unobserved, but, blending with the beauty of the eye itself,
     must command attention and sympathy!

     Whenever we behold a tear, let our kindliest sympathies awake--let
     it have a sacred claim upon all that we can do to succour and
     comfort under affliction. What rivers of tears have flown,
     excited by the cruel and perverse ways of man! War has spread its
     carnage and desolation, and the eyes of widows and orphans have
     been suffused with tears! Intemperance has blighted the homes of
     millions, and weeping and wailing have been incessant! A thousand
     other evils which we may conquer have given birth to tears enough
     to constitute a flood--a great tide of grief. Suppose we prize
     this little philosophy, _and each one determine never to excite a
     tear in another_. Watching the eye as the telegraph of the mind
     within, let us observe it with anxious regard; and whether we are
     moved to complaint by the existence of supposed or real wrongs,
     let the indication of the coming tear be held as a sacred truce to
     unkindly feeling, and our efforts be devoted to the substitution
     of smiles for tears!

[Verse: "Who is as the wise man? and who knoweth the interpretation
of a thing? a man's wisdom maketh his face to shine, and the boldness
of his face shall be changed."--ECCLESIASTES VIII.]

     There is only one other matter to which we think it necessary
     to allude, before we pass to the concluding section of our
     work. It has been said (162), that snow which is _white_, keeps
     the earth warm; that _white_ as a colour is _cool_, and that
     _black_ absorbs _heat_ (230). These assertions may appear to be
     contradictory, and, taken in connection with the fact of the
     blackness of the skin of negroes in hot climates, may at a first
     glance be considered unsatisfactory. They are, however, perfectly
     reconcileable, and that too, without the slightest evasion of
     the real bearing of the asserted facts. White snow is warm _on
     account of its texture_, which, being woolly, forms a layer of
     non-conducting substance over the surface of the earth, and _keeps
     in its warmth_; white clothing, worn as a garment consisting
     of a thin material, is cool, because _the white colour_ turns
     back the rays of the sun that fall upon it. Swansdown, although
     white, being a non-conductor, would be warm, because, though it
     would reflect the light and heat, it would confine and accumulate
     the heat of the body. The black skin of the negro is a _living
     texture_, and is not subject to the same laws that govern dead
     matter. The skin of the negro is largely provided with cells
     which secrete a fatty matter that acts as a non-conductor of the
     _external_ heat, and also a much larger number of perspiratory
     glands than exist in the skins of Europeans. The perspiration
     cools the blood, and carries off the _internal_ heat, while the
     oily matter gives a shining surface to the skin, and reflects
     the heat, to which the fatty matter presents itself as a
     non-conductor. We see, therefore, that there are two express
     provisions for the cooling of the negroes' skin, independent of
     the colour. The skin of the Esquimaux who inhabits a cold country
     is _white_, though it might be supposed that a black skin would
     best conduce to the warmth of his body. But the Esquimaux has,
     underneath his skin, _a thick coating of fat_, by which the
     _internal heat_ of the body is prevented from escaping.

     This _resume_ of the subjects embodied in the form of question
     and answer in the previous pages, will serve to impress the more
     important truths upon the mind of the reader, while it has enabled
     us to fill up many omissions necessitated by the arbitrary form of
     catechetical composition.

[Verse: "Ask now the beasts, and they shall teach thee; and the
fowls of the air, and they shall tell thee."--JOB XII.]




CHAPTER LII.


1029. _Why are there so many bodily forms in the animal creation?_

Because the various creatures which God has created have different
modes of life, and the forms of their bodies will be found to present
_a perfect adaptation to the lives allotted to them_.

Because, also, the beauty of creation _depends upon the variety of
objects of which it consists_. And the greatness of the Creator's power
is shown _by the diversity of ends accomplished by different means_.

1030. _Why are birds covered with feathers?_

Because they require a high degree of _warmth_, on account of the
activity of their muscles; but in providing that warmth it was
necessary that their coats should be of the _lightest material_, so as
not to impair their powers of flight; and feathers combine the _highest
warming power, with the least amount of weight_.

1031. _Why have ostriches small wings?_

Because, having long legs, they do not require their wings for flight;
they are merely used _to steady their bodies while running_.

1032. _Why are ostrich feathers soft and downy?_

Because, as the feathers are not employed for flight, the _strength of
the feather as constructed for flying is unnecessary_, and the feathers
therefore consist chiefly of a soft down.

1033. _Why have water-birds feathers of a close and smooth texture?_

Because such feathers keep the body of the bird warm and dry, by
repelling the water from their surface. A bird could scarcely move
through the water, with the downy feathers of the ostrich, because of
_the amount of water the down would absorb_.

1034. _Why is man born without a covering?_

Because _man is the only animal that can clothe itself_. As in the
various pursuits of life he wanders to every part of the globe, he can
adapt himself _to all climates and to any season_.

[Verse: "Who teacheth us more than the beasts of the earth, and
maketh us wiser than the fowls of heaven?"--JOB XXXV.]

1035. _Why do the furs of animals become thicker in the winter than in
the summer?_

Because the creator has thus provided for the preservation of the
warmth of the animals during the cold months of winter.

1036. _Why does a black down grow under the feathers of birds as winter
approaches?_

Because the down is a non-conductor of heat, and black the warmest
colour. It is therefore best adapted to _keep in_ their bodily warmth
during the cold of winter.

1037. _Why has man no external appendage to his mouth?_

Because _his hands_ serve all the purposes of gathering food, and
_conveying it to the mouth_. Man's mouth is simply an _opening_; in
other animals it is a _projection_.

1038. _Why have dogs, and other carnivorous animals, long pointed
teeth, projecting above the rest?_

Because as they have not hands to seize and controul their food, the
projecting teeth enable them to _snap and hold_ the objects which they
pursue for food.

1039. _Why is the under jaw of the hog, shorter and smaller than the
upper one?_

Because the animal pierces the ground _with its long snout_, and then
the small under jaw _works freely in the furrow_ that has been opened,
in quest of food.

1040. _Why have birds hard beaks?_

Because, having no teeth, the beak enables them to _seize_, _hold_, and
_divide their food_.

1041. _Why are the beaks of birds generally long and sharp?_

Because the greater number of birds live by _picking up small
objects_, such as worms, insects, seeds, &c. The sharp beak, therefore,
serves as a _fine pincers_, enabling them to take hold of their food
conveniently.

[Verse: "As the fishes that are taken in an evil net, and as the
birds that are caught in the snare; so are the sons of men snared in an
evil time, when it falleth suddenly upon them."--ECCLESIASTES IX.]

1042. _Why have snipes and woodcocks long tapering bills?_

Because they live upon worms which they find in the soft mud of streams
and marshy places; their long bills, therefore, enable them to _dig
down into the mud after their prey_.

1043. _Why have woodcocks, snipes, &c., nerves running down to the
extremities of their bills?_

Because, as they dig for their prey in the soft sand and mud, they
cannot see the worms upon which they live. Nerves are, therefore,
distributed to the very point of their bills (where, in other birds,
nerves are entirely absent) _to enable them to prehend their food_.

[Illustration: Fig. 67.--SPOONBILL.]

1044. _Why have ducks and geese square-pointed bills?_

Because they not only feed by dabbling in soft and muddy soil, but they
consume a considerable quantity of green food, and their square bills
enable them to _crop off the blades of grass_.

[Verse: "Let the heaven and earth praise him, the seas, and
everything that moveth therein."--PSALM LXIX.]

1045. _Why has the spoon-bill a long expanded bill, lined internally
with sharp muscular points?_

Because the bird _lives by suction_, dipping its broad bill in search
of aquatic worms, mollusks, insects and the roots of weeds. The bill
forms _a natural spoon_, and the muscular points enable the bird to
_filter the mud_, and to retain the nourishment which it finds.

1046. _Why has the spoon-bill long legs?_

Because it _wades in marshy places_ to find its food. Its legs are
therefore long, for the purpose of keeping its body out of the water,
and above the smaller aquatic plants, while it searches for its prey.

1047. _Why have the parrots, &c., crooked and hard bills?_

Because they live upon nuts, the stones of fruit, and hard seeds. The
shape of the bill, therefore, enables them to _hold the nut or seed
firmly_, and the sharp point enables them to _split or remove the
husks_.

1048. _Why can a parrot move its upper as well as its lower bill?_

Because by that means it is enabled to bring the nut or seed nearer
the fulcrum, or joint of the jaw. It, therefore, acquires greater
power, just as with a pair of nut-crackers we obtain increased power by
_setting the nut near to the joint_.

1049. _Why have animals with long necks large throats?_

Animals that graze, or feed from the ground, generally have a more
powerful muscular formation of the throat than those which feed in
other positions, because a greater effort is required to _force the
food upward, than would be needed to convey it down_.

1050. _Why are the bones of birds hollow?_

Because they are thereby rendered _lighter_, and do not interfere with
the flight of the bird _as they would do if they were solid_. Greater
strength is also obtained by the _cylindrical form of the bone_, and a
larger surface afforded for the _attachment of powerful muscles_.

[Verse: "And my hand hath found, as a nest, the riches of the
people; and as one gathereth eggs that are left, have I gathered all
the earth; and there was none that moved the whip, or opened the mouth,
or peeped."--ISAIAH X.]

1051. _Why do all birds lay eggs?_

Because, to bear their young in any other manner, would _encumber the
body_, and materially interfere with their powers of flight.

As soon as an egg becomes large and heavy enough to be cumbersome to
the bird, it is removed from the body. A shell, impervious to air,
protects the germ of life within, until from two to twenty eggs have
accumulated, and then, although laid at different intervals, their
incubation commences together, and the young birds are hatched at the
same time.




CHAPTER LIII.


1052. _Why have birds with long legs short tails?_

Because the tails of birds are used to guide them through the air, by
a _kind of steerage_. When birds with long legs take to flight, they
throw their legs behind, and they then _serve the same purpose as a
tail_.

[Illustration: Fig. 68.--PERCH.]

1053. _Why have fishes fins?_

The fins of fishes are to them, _what wings and tails are to birds_,
enabling them to rise in the fluid in which they live by the _reaction
of the motions of the fins upon its substance_.

[Verse: "Speak to the earth, and it shall teach thee; and the fishes
of the sea shall declare unto thee. Who knoweth not in all these that
the hand of the Lord hath wrought this."--JOB XII.]

1054. _Why are the fins of fishes proportionately so much smaller than
the wings of birds?_

Because there is less difference between the _specific gravity_ of the
body of a fish, and the water in which it moves, than between the body
of a bird, and the air on which it flies. The fish, therefore _does not
require such an expanded surface to elevate or guide it_.

1055. _Why have fishes scales?_

Because scales, while they afford protection to the bodies of fish,
are conveniently adapted to their motions; and as the scales _present
no surface to obstruct their passage through the water_, as hair or
feathers would do, they evidently form the best covering for the
aquatic animal.

1056. _Why do fishes float in streams (when they are not swimming) with
their heads towards the stream?_

Because they _breathe_ by the transmission of water over the surface
of their gills, the water entering at the mouth, and passing over the
gills behind. When, therefore, they lie motionless with their heads to
the stream, they are in _that position which naturally assists their
breathing process_.

1057. _Why have fishes air-bladders?_

Because, as the density of water varies greatly at different depths,
the enlargement or contraction of the bladder regulates the relation of
_the specific gravity of the body of the fish to that of the water in
which it moves_.

1058. _Why have whales a very large development of oily matter about
their heads?_

Because their heads are thereby rendered the lighter part of their
bodies, and a very slight exertion on the part of the animal will bring
its head to the surface _to breathe air, which it constantly requires_.

1059. _Why have birds that swim upon water web-feet?_

Because the spreading out of the toes of the bird brings the membrane
between the toes into the form of a fin, or _water-wing_, by striking
which against the water, _the bird propels itself along_.

[Verse: "And Jesus saith unto him, The foxes have holes, and the
birds of the air have nests; but the son of man hath not where to lay
his head."--MATTHEW XIII.]

1060. _Why have birds that swim and dive short legs?_

Because long legs would greatly _impede their motions in the water_, by
becoming repeatedly entangled in the weeds, and by striking against the
bottom. _Waders_, however, require long legs because they have to move
about through the _tall vegetation of marshy borders_.

[Illustration: Fig. 69.--STILT-PLOVER AND DUCK.]

1061. _Why have the feet of the heron, cormorant, &c., deep rough
notches upon their under surface?_

Because, as those birds live by catching fish, they are enabled by the
notches in their feet, to _hold the slippery creatures upon which they
feed_.

1062. _Why have otters, seals, &c., web-feet?_

Because, while the feet enable them to _walk upon the land_, they are
equally effective in their action upon the water, and hence they are
_adapted to the amphibious nature of the animals to which they belong_.

1063. _Why do the external ears of animals of prey, such as cats,
tigers, foxes, wolves, hyenas, &c., bend forward?_

Because they collect the sounds that occur _in the direction of the
pursuit_, and enable the animal to _track its prey_ with greater
certainty.

[Verse: "Doth the hawk fly by thy wisdom, and stretch her wings
toward the south? "Doth the eagle mount up at thy command, and make her
nest on high?"]

1064. _Why do the ears of animals of flight, such as hares, rabbits,
deer, &c., turn backward?_

Because they thereby catch the sounds that give them _warning of the
approach of danger_.

1065. _Why has the stomach of the camel a number of distinct bags, like
so many separate stomachs?_

Because water is stored up in the separate chambers of the stomach,
apart from the solid aliment, so that the animal can _feed_, without
consuming all its drink. It is thereby _able to retain water to satisfy
its thirst while travelling across hot deserts_, where no water could
be obtained.

1066. _Why do woodpeckers "tap" at old trees?_

Because by boring through the decayed wood, with the sharp and hard
bills with which they are provided, _they get at the haunts of the
insects upon which they feed_.

1067. _Why are woodpeckers' tongues about three times longer than their
bills?_

Because, if their bills were long, they would not bore the trees so
efficiently; and when the trees are bored, and the insects alarmed,
they endeavour to retreat into the hollows of the wood; _but the long
thin tongue of the woodpecker fixes them on its sharp horny point_, and
draws them into the mouth of the bird.

1068. _Why have the Indian hogs large horns growing from their nostrils
and turning back towards their eyes?_

Because the horns _serve as a defence to the eyes_ while the animal
forces its way through the thick underwood in which it lives.

1069. _Why have calves and lambs, and the young of horned cattle
generally, no horns while they are young?_

Because the presence of horns would _interfere with the suckling
of the young animal_. When, however, it is able to feed itself by
browsing, _then the horns begin to grow_.

[Verse: "She dwelleth and abideth on the rock, upon the crag of the
rock, and the strong place.

"From thence she seeketh the prey, and her eyes behold afar off. Her
young ones also suck up blood: and where the slain are, there is
she."--JOB XXXIX.]

1070. _Why have infants no teeth?_

Because the presence of teeth would interfere with their suckling,
while the teeth would be of no service, until the child _could take
food requiring mastication_.

1071. _Why cannot flesh-eating animals live upon vegetables?_

Because the gastric juice of a flesh-eating animal, being adapted to
the duty which it has to perform, _will not dissolve vegetable matter_.

1072. _Why have birds gizzards?_

Because, having no teeth, the tough and fibrous gizzards are employed
_to grind the food preparatory to digestion_.

1073. _Why are small particles of sand, stone, &c., found in the
gizzards of birds?_

Because, by the presence of those rough particles, which become
embedded in the substance of the gizzard, the food of the bird is more
effectively ground.

     When our fowls are abundantly supplied with meat, they soon fill
     their craw, but it does not immediately pass thence into the
     gizzard; it always enters in small quantities, in proportion
     to the progress of trituration, in like manner, as in a mill,
     a receiver is fixed above the two large stones which serve for
     grinding the corn, which receiver, although the corn be put
     into it by bushels, allows the grain to dribble only in small
     quantities into the central hole in the upper mill-stone.--_Paley._




CHAPTER LIV.


1074. _Why has the mole hard and flat feet, armed with sharp nails?_

Because the animal is thereby enabled to _burrow in the earth_, in
search for worms. Its feet are so many _shovels_.

1075. _Why is the mole's fur exceedingly glossy and smooth?_

Because its smoothness enables it to work under ground _without the
soil sticking to its coat_, by which its progress would be impeded.
From soils of all kinds, the little worker emerges shining and clean.

[Verse: "I know all the fowls of the mountains, and the wild beasts
are mine."--PSALM L.]

     What I have always most admired in the mole is its _eyes_. This
     animal occasionally visiting the surface, and wanting, for its
     safety and direction, to be informed when it does so, or when it
     approaches it, a perception of light was necessary. I do not know
     that the clearness of sight depends at all upon the size of the
     organ. What is gained by the largeness or prominence of the globe
     of the eye, is width in the field of vision. Such a capacity would
     be of no use to an animal which was to seek its food in the dark.
     The mole did not want to look about it; nor would a large advanced
     eye have been easily defended from the annoyance to which the life
     of the animal must constantly expose it. How indeed was the mole,
     working its way under ground, to guard its eyes at all? In order
     to meet this difficulty, the eyes are made scarcely larger than
     the head of a corking-pin; and these minute globules are sunk so
     deeply in the skull, and lie so sheltered within the velvet of
     its covering, as that any contraction of what may be called the
     eyebrows, not only closes up the apertures which lead to the eyes,
     but presents a cushion, as it were, to any sharp or protruding
     substance which might push against them. This aperture, even in
     its ordinary state, is like a pin-hole in a piece of velvet,
     scarcely pervious to loose particles of earth.--_Paley._

[Illustration: Fig. 70.--ELEPHANTS DRINKING.]

1076. _Why has the elephant a short unbending neck?_

Because the elephant's head is so heavy, that it could not have been
supported at the end of a long neck (or lever), without _a provision of
immense muscular power_.

[Verse: "Be not afraid, ye beasts of the field: for the pastures of
the wilderness do spring, for the tree beareth her fruit, the fig-tree
and the vine do yield their strength."--JOEL II.]

1077. _Why has the elephant a trunk?_

The trunk of an elephant _serves as a substitute for a neck_, enabling
the animal to crop the branches of trees, or to raise water from the
stream.

1078. _Why do the hind legs of elephants bend forward?_

Because the weight of the animal is so great, that when it lay down it
would _rise with great difficulty_, if its legs bent outward, as do the
legs of other animals. Being bent _under the body_, they have a greater
power of pushing directly upward, when the powerful muscles of the
thighs straighten them.

     According to Cuvier, the number of muscles, in an elephant's
     trunk, amounts to _forty thousand_, all of which are under the
     will, and it is to these that the proboscis of this animal owes
     its flexibility. It can be protruded or contracted at pleasure,
     raised up or turned to either side, coiled round on itself or
     twined around any object. With this instrument the elephant
     collects the herbage on which he feeds and puts it into his mouth;
     with this he strips the trees of their branches, or grasps his
     enemy and dashes him to the ground. But this admirable organ is
     not only adapted for seizing or holding substances of magnitude;
     it is also capable of plucking a single leaf, or of picking up a
     straw from the floor. The orifices of the canals of the extremity
     are encircled by a projecting margin, produced anteriorly into
     a finger-like process endowed with a high degree of sensibility
     and exceedingly flexible. It is at once a finger for grasping and
     a feeler: the division between the two nasal orifices or their
     elevated sides serves as a point against which to press; and thus
     it can pick up or hold a small coin, a bit of biscuit, or any
     trifling thing with the greatest ease.--_Knight's Animal Kingdom._

1079. _Why have bats hooked claws in their wings?_

Because bats are almost destitute of legs and feet; at least those
organs are included in their wings. If they alight upon the ground,
they have great difficulty in again taking to the wing, as they cannot
run or spring to bring their wings in action upon the air. At the angle
of each wing there is placed, therefore, a bony hook, by which the bat
attaches itself to the sides of rocks, caves, and buildings, laying
hold of crevices, joinings, chinks, &c.; and when it takes its flight,
_it unhooks itself, and its wings are at once free to strike the air_.

1080. _Why does the bat fly by night?_

Because it lives chiefly upon moths, which are _night-flying insects_.

[Verse: "So are the paths of all that forget God; and the
hypocrite's hope shall perish: Whose hope shall be cut off, and whose
trust shall be a spider's web."--JOB VIII.]

1081. _Why does the bat sleep during the winter?_

Because, as the winter approaches, the moths and flying insects upon
which it feeds, disappear. _If, therefore, it did not sleep through the
winter it must have starved._

[Illustration: Fig. 71.--BAT WITH HOOKED WINGS.]

1082. _Why has the spider the power of spinning a web?_

Because, as it lives upon flies, but is _deficient of the power of
flying in pursuit of them_, it has been endowed with an instinct _to
spread a snare to entrap them_, and with the most wonderful machinery
to give that instinct effect.

     There are few things better suited to remove the disgust into
     which young people are betrayed on the view of some natural
     objects, than this of the spider. They will find that the most
     despised creature may become a subject of admiration, and be
     selected by the naturalist to exhibit the marvellous works of the
     creation. The terms given to these insects, lead us to expect
     interesting particulars concerning them, since they have been
     divided into vagrants, hunters, swimmers, and water spiders,
     sedentary, and mason-spiders; thus evincing a variety in their
     condition, activity, and mode of life; and we cannot be surprised
     to find them varying in the performance of their vital functions
     (as, for example, in their mode of breathing), as well as in
     their extremities and instruments. Of these instruments the most
     striking is the apparatus for spinning and weaving, by which they
     not only fabricate webs to entangle their prey, but form cells for
     their residence and concealment; sometimes living in the ground,
     sometimes under water, yet breathing the atmosphere. Corresponding
     with their very singular organisation are their instincts. We are
     familiar with the watchfulness and voracity of some spiders, when
     their prey is indicated by the vibration of the cords of their
     net-work. Others have the eye and disposition of the lynx or
     tiger, and after couching in concealment, leap upon their victims.
     Some conceal themselves under a silken hood or tube, six eyes only
     projecting. Some bore a hole in the earth, and line it as finely
     as if it were done with the trowel and mortar, and then hang it
     with delicate curtains. A very extraordinary degree of contrivance
     is exhibited in the trap-door spider. This door, from which it
     derives its name, has a frame and hinge on the mouth of the cell,
     and is so provided that the claw of the spider can lay hold of
     it, and whether she enters or goes out, says Mr. Kirby, the door
     shuts of itself. But the water-spider has a domicile more curious
     still: it is under water, with an opening at the lower part for
     her exit and entrance; and although this cell be under water, it
     contains air like a diving-bell, so that the spider breathes the
     atmosphere. The air is renewed in the cell in a manner not easily
     explained. The spider comes to the surface; a bubble of air is
     attracted to its body; with this air she descends, and gets under
     her cell, when the air is disengaged and rises into the cell; and
     thus, though under water, she lives in the air. There must be some
     peculiar property of the surface of this creature by which she can
     move in the water surrounded with an atmosphere, and live under
     the water breathing the air.

[Verse: "The spider taketh hold with her hands, and is in king's
palaces."--PROVERBS XXX.]

[Illustration: Fig. 72.--WEB OF THE GEOMETRICAL SPIDER.]

     The chief instrument by which the spider performs these wonders is
     the spinning apparatus. The matter from which the threads are spun
     is the liquid contained in cells; the ducts from these cells open
     upon little projecting teats, and the atmosphere has so immediate
     an effect upon this liquid, that upon exposure to it the secretion
     becomes a tough and strong thread. Twenty-four of these fine
     strands form together a thread of the thickness of that of the
     silk-worm. We are assured that there are three different sorts of
     material thus produced, which are indeed required for the various
     purposes to which they are applied--as, for example, to mix up
     with the earth to form the cells; to line these cells as with fine
     cotton; to make light and floating threads by which they may be
     conveyed through the air, as well as those meshes which are so
     geometrically and correctly formed to entrap their prey.--_Note by
     Lord Brougham to Paley's Natural Theology._


[Verse: "For every beast of the forest is mine, and the cattle upon
a thousand hills."--PSALM L.]

1083. _Why have many insects a great number of eyes?_

Because the orb of the eye is fixed; there is therefore placed over
the eye a multiple-lens, which conducts light to the eye from every
direction; so that _the insect can see with a fixed eye as readily as
it could have done with a movable one_. As many as fourteen hundred
eyes, or inlets of light, have been counted in the head of a drone-bee.
The spider has _eight eyes_, mounted upon different parts of the head;
two in front, two in the top of the head, and two on each side.

1084. _Why have birds of prey no gizzards?_

Because their food _does not require to be ground_ prior to digestion,
as does the food of grain-eating birds.

1085. _Why have earth worms no feet?_

Because the undulatory motion of their muscles serves them for fill the
purposes of progression _needed by their mode of life_.

1086. _Why have mussels strong tendinous threads proceeding from their
shells?_

Because as they live in places that are beaten by the surf of the sea,
they _moor their shells_ by those threads to rocks and timbers.

1087. _Why have cockles stiff muscular tongues?_

Because, having no threads to moor themselves, as the mussels have,
they _dig out with their tongues a shelter for themselves in the sand_.

1088. _Why do oxen, sheep, deer, &c., ruminate?_

Because they have no front teeth in the upper jaw, the place of which
is occupied by a hardened gum. The first process, therefore, consists
simply of _cropping_ their food, which is passed into the paunch, to
_be brought up again and ground by the back teeth_ when the cropping
process is over.

Because, in a wild state, they are constantly exposed to the attacks
of carnivorous beasts, and as the mastication of the large amount of
vegetable food required for their sustenance would take a considerable
time, they are provided with stomachs, by which they are enabled to
fill their paunches quickly, and then, retiring to a place of safety,
they bring their food up again, and chew it at leisure.

[Verse: "A righteous man regardeth the life of his beast: but the
tender mercies of the wicked are cruel."--PROVERBS XII.]

1089. _Why can ruminating animals recover the food from their paunches?_

Because they have a _voluntary power_ over the muscles of the throat,
by which they can bring up the food at will.

1090. _Why can they keep the unchewed food in the paunch, from the
"cud" they have chewed for nourishment?_

Because their stomachs are divided into three chambers: 1, the
_paunch,_ where the unchewed food is stored; 2, the _reticulum_, where
portions of the food are received from the paunch, and moistened and
rolled into a "cud," to be sent up and chewed; and 3, the _psalterium_,
which receives the masticated food, and continues the process of
digestion.

     In quadrupeds the deficiency of teeth is usually _compensated_
     by the faculty of rumination. The sheep, deer, and ox tribe, are
     without fore-teeth in the upper jaw. These ruminate. The horse
     and ass are furnished with teeth in the upper jaw, and do not
     ruminate. In the former class, the grass and hay descend into the
     stomachs nearly in the state in which they are cropped from the
     pasture, or gathered from the bundle. In the stomach, they are
     softened by the gastric juice, which in these animals is unusually
     copious. Thus softened and rendered tender, they are returned a
     second time to the action of the mouth, where the grinding teeth
     complete at their leisure the trituration which is necessary;
     but which was before left imperfect. I say, the trituration
     which is necessary; for it appears from experiments, that the
     gastric fluid of sheep, for example, has no effect in digesting
     plants, unless they have been previously masticated; that it only
     produces a slight maceration, nearly as common water would do in
     a like degree of heat; but that when once vegetables are reduced
     to pieces by mastication, the fluid then exerts upon them its
     specific operation. Its first effect is to soften them, and to
     destroy their natural consistency; it then goes on to dissolve
     them, not sparing even the toughest parts, such as the nerves of
     the leaves. I think it very probable, that the gratification also
     of the animal is renewed and prolonged by this faculty. Sheep,
     deer, and oxen, appear to be in a state of enjoyment whilst they
     are chewing the cud. It is then, perhaps, that they best relish
     their food.--_Paley._

[Verse: "I am like a pelican of the wilderness: I am like an owl
of the desert. I watch, and am as a sparrow alone upon the house
top."--PSALM CII.]




CHAPTER LV.


1091. _Why do quadrupeds that are vegetable eaters feed so continually?_

Because their food contains but a _small proportion of nutrition_, so
that it is necessary to digest a _large quantity_ to obtain sufficient
nourishment.

1092. _Why do flesh eating animals satisfy themselves with a rapid
meal?_

Because the food which they eat is _rich in nutritious matter_, and
more readily digestible than vegetable food; it does not therefore,
require the same amount of _grinding with the teeth_.

[Illustration: Fig. 73.--PELICAN WITH DILATED POUCH.]

1093. _Why has the pelican a large pouch under its bill?_

Because it subsists upon fish, generally of the smaller kind, and uses
its pouch _as a net_ for catching them; the pouch also serves as a
_paunch,_ in which the fish are stored, until the bird ceases from the
exertion of fishing, and takes its meal at leisure.

[Verse: "And God created great whales, and every living creature
that moveth, which the waters brought forth abundantly, after their
kind, and every winged fowl after his kind: and God saw that it was
good."--GENESIS I.]

     In their wild state they hover and wheel over the surface of the
     water, watching the shoals of fish beneath, and suddenly sweeping
     down, bury themselves in the foaming waves; rising immediately
     from the water by their own buoyancy, up they soar, the pouch
     laden with the fish scooped up during their momentary submersion.
     The number of fish the pouch of this species will contain may be
     easily imagined when we state that it is so dilatable as to be
     capable of containing two gallons of water; yet the bird has the
     power of contracting this membranous expansion, by wrinkling it
     up under the lower mandible, until it is scarcely to be seen. In
     shallow inlets, which the pelicans often frequent, it nets its
     prey with great adroitness.

     The pelican chooses remote and solitary islands, isolated rocks in
     the sea, the borders of lakes and rivers, as its breeding place.
     The nest, placed on the ground, is made of coarse grasses, and
     the eggs, which are white, are two or three in number. While the
     female is incubating, the male brings fish to her in his pouch,
     and the young, when hatched, are assiduously attended by the
     parents, who feed them by pressing the pouch against the breast,
     so as to transfer the fish from the former into the throats of the
     young. This action has doubtless given origin to the old fable
     of the pelican feeding its young with blood drawn from its own
     breast.--_Knight's Animal Kingdom._

1094. _Why do the smaller animals breed more abundantly than the larger
ones?_

Because the smaller ones are designed to be the food of the larger
ones, and are therefore _created in numbers adapted to that end_.
An elephant produces but one calf; the whale but one young one; a
butterfly lays six hundred eggs; silk-worms lay from 1,000 to 2,000
eggs; the wasp, 5,000; the ant, 4,000 to 5,000; the queen bee, 5,000
to 6,000, or 40,000 to 50,000 in a season; and a species of white ant
(_termes fatalis_) produces 86,400 eggs in a day. Birds of prey seldom
produce more than two eggs; the sparrow and duck tribe frequently sit
upon a dozen; in rivers there prevail a thousand minnows for one pike;
and in the sea, a million of herrings for a single shark; while of the
animalcules upon which the whale subsists, there must exist hundreds of
millions for one whale.

1095. _Why has the whale feathery-like laminæ of whale-bone extending
from its jaws?_

Because these feathery bones, lying side by side, form a _sieve, or
strainer_, for the large volumes of water which the whale receives into
its mouth, drawing off therefrom millions of small animals, which form
a jelly-like mass upon which the whale feeds. A whale has been known
to weigh as much as 249 tons, and its blubber yielded 4,000 gallons of
oil. How many millions of living creatures must have gone to make up
that enormous mass of animal matter!

[Verse: "Hast thou given the horse strength? hast thou clothed his
neck with thunder? * * He paveth the valley, and rejoiceth in his
strength: he goeth on to meet the armed men."--JOB XXXIX.]

1096. _Why have cats, and various other animals, whiskers?_

The whiskers of cats, and of the cat tribe, are exceedingly sensitive,
enabling them, when seizing their prey in the dark, to _feel its
position most acutely_. These hairs are supplied, through their roots,
with branches of the same nerves that give sensibility to the lips, and
that in insects _supply their "feelers."_

1097. _Why has the horse a smaller stomach proportionately than other
animals?_

Because the horse was created for speed. Had he the ruminating stomach
of the ox, he would be quite unfitted for the labour which he now so
admirably performs.

1098. _Why has the horse no gall-bladder?_

Because the rapid digestion of the horse, by which its fitness for
speed is greatly increased, _does not require the storing up of the
bile_ as in other animals in which the digestive process is a slower
operation.

1099. _Why do certain butterflies lay their eggs upon cabbage leaves?_

Because the cabbage leaves are _the food of the young caterpillars_;
and although the butterfly does not subsist herself upon the leaf, she
knows by instinct that the leaf will afford food to her future young;
she therefore lays her eggs where her young ones will find food.

     This explanation applies to many insects that lay their eggs upon
     other plants.

1100. _Why have insects long projections from their heads, like horns
or feathers?_

Because those organs (the _antennæ_), are those through which come
insects _hear_ and others _feel_; and the projecting of these _antennæ_
from their bodies probably enables them to hear or feel more acutely
while their wings are in motion, _without the interference of the
vibrations of their wings_.

[Verse: "My son, eat thou honey, because it is good; and the
honey-comb, which is sweet to thy taste."--PROVERBS XXIV.]

1101. _Why have bees stings?_

Because they gather and store up honey which would constantly attract
other insects, and the bees would be robbed of their food but for the
sting, _which is given to them for protection_.

1102. _Why have flies fine hairs growing at the extremities of their
legs?_

Because they require to cleanse their bodies and wings, and to free
them from particles of dust. And as they cannot turn their heads for
this purpose, they have hairy feet, which serve as brushes, by which
any part of their bodies can be reached and cleaned.




CHAPTER LVI.


1103. _Why when the perfume of flowers is unusually perceptible may wet
weather be anticipated?_

Because when the air is damp it _conveys the odours of flowers_ more
effectively than it does when dry.

1104. _Why when swallows fly low may wet weather be expected?_

Because the insects which the swallows pursue in their flight are
flying low, _to escape the moisture of the upper regions of the
atmosphere_.

1105. _Why do ducks and geese go to the water, and dash it over their
backs on the approach of rain?_

Because by wetting the outer coat of their feathers before the rain
falls, by sudden dashes of water over the surface, they _prevent the
drops of rain from penetrating to their bodies through the open and dry
feathers_.

1106. _Why do horses and cattle stretch out their necks and snuff the
air on the approach of rain?_

Because they smell the _fragrant perfume_ which is diffused in the air
by its increasing moistness.

[Verse: "I will remember the works of the Lord: Surely I will
remember thy wonders of old."--PSALM LXXVII.]

1107. _Why may change of weather be anticipated when domestic animals
are restless?_

Because their skins are exceedingly sensitive to atmospheric
influences, and they are oppressed and irritated by _the changing
condition of the atmosphere_.

1108. _Why may fine weather be expected when spiders are seen busily
constructing their webs?_

Because those insects are highly sensitive to the state of the
atmosphere, and when it is setting fine they build their webs, because
they know instinctively _that flies will be abroad_.

1109. _Why is wet weather to be expected when spiders hide?_

Because it shows that they are aware that the state of the atmosphere
does not _favour the flight of insects_.

1110. _Why if gnats fly in large numbers may fine weather be expected?_

Because it shows that they feel the state of the atmosphere to be
favourable, which induces them all to _leave their places of shelter_.

1111. _Why if owls scream during foul weather, will it change to fine?_

Because the birds are pleasurably excited by a favourable _change in
the atmosphere_.

1112. _Why is it said that the moping of the owl foretells death?_

Because owls scream when the weather is on the change; and when a
patient is lingering on a death bed, the alteration in the state of the
atmosphere frequently induces death, because the faint and expiring
flame of life has not strength enough _to adapt itself to the change_.

1113. _Why may wet weather be expected when spiders break off their
webs, and remove them?_

Because the insects, anticipating the approach of rain, remove their
webs for preservation.

[Verse: "There shall the great owl make her nest, and lay, and
hatch, and gather under her shadow: there shall the vultures also be
gathered, every one with her mate."--ISAIAH XXXIV.]

1114. _Why may we expect a continuance of fine weather when bees wander
far from their hives?_

Because the bees feel instinctively that from the state of the
atmosphere they may wander far in search of honey, without the danger
of being overtaken by rain.

1115. _Why if people feel their corns ache, and their bones rheumatic,
may rain be expected?_

Because the dampness of the atmosphere affects its pressure upon the
body, and causes a temporary disturbance of the system. All general
disturbances of the body, _manifest themselves in those parts which are
in a morbid state_--as in a corn, a rheumatic bone, or a decayed tooth.

1116. _Why if various flowers close may rain be expected?_

Because plants are highly sensitive to atmospheric changes, and _close
their petals to protect their stamens_.

1117. _Why when moles throw up their hills may rain be expected?_

Because the moles know instinctively, that on the approach of wet,
worms move in the ground; the moles therefore become active, _and form
their hills_.

1118. _Why is a magpie, when seen alone, said to foretell bad weather?_

Because magpies generally fly in company; but on the approach of wet or
cold, one _remains in the nest to take care of the young_, while the
other one wanders alone in search of food.

1119. _Why do sea-gulls appear numerous in fine weather_?

Because the fishes swim near to the surface of the sea, and the birds
_assemble over the sea to catch the fish, instead of sitting on rocks_,
or wading on the shore.

1120. _Why do sea-gulls fly over the land, on the approach of stormy
weather?_

Because in stormy weather they cannot catch fish; and the _earth-worms
come up on the land_ when the rain falls.

[Verse: "And I said, Oh, that I had wings like a dove! for then
would I fly away, and be at rest."--PSALM LV.]

1121. _Why if birds cease to sing, may wet, and probably thunder, be
expected._?

Because birds are depressed by an unfavourable change in the
atmosphere, and _lose those joyful spirits which give rise to their
songs_.

1122. _Why if cattle run around in meadows, may thunder be expected?_

Because the electrical state of the atmosphere has the effect of making
them feel uneasy and irritable, and _they chase each other about to get
rid of the irritability_.

1123. _Why if birds of passage arrive early, may severe weather be
expected?_

Because it shows that the indications of unfavourable weather have set
in, in the latitudes from which the birds come, and that they have
_taken an early flight to escape it_.

1124. _Why if the webs of the gossamer spider fly about in the autumn,
may east winds be anticipated?_

Because an east wind is a dry and dense wind, and suitable to the
flight of the gossamer spider; the spider feeling instinctively the
dryness of the air, throws out its web, and finds it _more than usually
buoyant upon the dense air_.

     The observation of the changing phenomena which attend the various
     states of the weather is a very interesting study, though no
     general rules can be laid down that can be relied upon, because
     there are modifying circumstances which influence the weather in
     various localities and climates. To observe weather indications
     accurately, no phenomenon should be taken alone, but several
     should be regarded together. The character and the duration of
     the weather of the preceding days, the direction of the wind,
     the forms of the clouds, the indications of the barometer, the
     rise or fall of the thermometer, and the instinctive forewarnings
     of birds, beasts, insects, and flowers, should all be taken
     into account. Although no direct material advantages attend
     such a study, it induces a habit of observation, and develops
     the inductive faculty of the mind, which, when applied to more
     significant things, may trace important effects to their greater
     causes.

[Verse: "Go to the ant, thou sluggard; consider her ways, and be
wise."--PROV. VI.]




CHAPTER LVII.


1125. _Why can gossamer spiders float through the air?_

Because, having no wings, and being deficient in the active muscular
powers of other spiders, they have been endowed with the power of
spinning a web which is so light that it floats in the air, and bears
the body of the gossamer spider from place to place. Each web acts as a
balloon, and the spider attached thereto is a little _aeronaut_.

1126. _Why do crickets make a peculiar chirping sound?_

Because they have hard wing cases, by the friction of the edges of
which they cause their peculiar noise, _to make known to each other
where they are_, in the dark crevices in which they hide.

[Illustration: Fig. 74.--GLOW-WORM USING HIS BRUSH.]

1127. _Why has the glow-worm a brush attached to its tail?_

Because it is necessary to keep its back very clean, that _the light
which its body emits may not be dimmed_.

1128. _Why does the glow-worm emit a light?_

Because the female glow-worm is without wings, but the male is a winged
insect. The female, therefore, is endowed with the power of displaying
a phosphorescent light. The light is only visible by night, but it is,
nevertheless, beautifully adapted for the purpose stated, because the
_male is a night-flying insect_, and never ventures abroad by day.

[Verse: "They that go down to the sea in great ships, that do
business in great waters these see the works of the Lord, and his
wonders in the deep."--PSALM CVII.]

     There exists some difference of opinion between naturalists upon
     the uses of the light of a glow-worm; there are some who doubt
     that it is exhibited to attract the flying insect. The objectors,
     however, offer no explanation of the luminous properties of the
     worm. Sir Charles Bell says the preponderance of the argument is
     decidedly in favour of the explanation we have given.

1129. _Why does not the iris of the fish's eye contract_?

Because the diminished light in water is _never too strong for the
retina_.

1130. _Why is the eye of the eel covered with a transparent horny
covering?_

Because, as the eel lives in holes, and pushes its head into mud, and
under stones, &c., it needed such a covering to _defend the eye_.

1131. _Why is the whale provided with an eye, having remarkably thick
and strong coats?_

Because, when he is attacked by the sword-fish and the shark, he is
almost helpless against his enemies, as they fix themselves upon his
huge carcase. He therefore dives with them down to a depth where the
pressure of the water is so great that they cannot bear it. The eye
of the whale is expressly organised _to bear the immense pressure of
extreme ocean depths_, without impairing the sight.

1132. _Why have fishes no eyelids?_

Because the water in which they swim keeps their eyes moist. Eyelids
would therefore be _useless to them_.

1133. _Why have fishes the power of giving their eye-balls very sudden
motion?_

Because, having no eyelids (such organs being unnecessary to keep their
eyes moist), they still need the power of freeing their eyes from the
contact of foreign matters; and this is secured to them by the power
they have of giving the eyeball a very rapid motion, which causes
reaction in the fluid surrounding it, and _sweeps the surface_.

     This motion may frequently be seen in the eyes of fishes, in glass
     globes.

[Verse: "And God made the beast of the earth after his kind, and
cattle after their kind, and everything that creepeth upon the earth
after his kind: and God saw that it was good."--GENESIS I.]

1134. _Why is the lachrymal secretion of the horse's eye thick and
glutinous?_

Because, as his eye is large, and constantly exposed to dust on
journeys, it is provided with a _viscid secretion_, which cleanses the
eye, and more instantly and securely removes the dust, than a _watery_
secretion would.

1135. _Why does the lower bill of the sea-crow project beyond the upper
one?_

Because the bird obtains his food by _skimming along the water_, into
which he dips his bill, and lifts his food out.

1136. _Why do the mandibles of the cross-bill overlap each other?_

Because the bird requires a peculiar bill, to enable it to _split seeds
into halves_, and to tear the open cones of the fir-tree.

1137. _Why are the tails of fishes so much larger than their fins?_

Because their tails are their _chief instruments of motion_, while
their fins are employed simply to direct their progress, and steady
their movements.

1138. _Why have oxen, and other quadrupeds a tough ligament called the
"pax-wax," running from their backs to their heads?_

Because their heads are of considerable weight; and having frequent
occasion to lift them, they are provided with an elastic ligament,
which is fastened at the middle of their backs, while its other
extremity is attached to the head. This enables them to raise their
heads easily; otherwise the effort to do so would be a work of great
labour. To the horse, the pax-wax acts as a natural bearing-rein,
assisting it to hold its head in that position which adds to the grace
and beauty of the animal.

     In carving beef, this ligament may be seen passing along the
     vertebræ of the neck, the chuck, and the fore ribs.

[Verse: "He shall feed his flock like a shepherd; he shall gather
the lambs with his arm, and carry them in his bosom, and shall gently
lead those that are with young."--ISAIAH XL.]

1139. _Why have the females of the kangaroo and opossum tribes pouches,
or pockets, formed in the skin of their breasts for the reception of
their young?_

Because their young ones are remarkably _small and helpless_; in fact,
more so than those of any other animal of equal proportions. Besides
which, the full grown animals have very long hind-legs, and they
progress by a series of extraordinary leaps. It would consequently
be impossible for their helpless young ones to follow them: God has
therefore given to female kangaroos and opossums curious pockets,
_formed out of their own skin_, in which they place their little young
ones, and bear them through their surprising leaps with the greatest
ease and safety.




CHAPTER LVIII.


1140. _What is the difference between an animal, a plant, and a
mineral?_

The great naturalist, Linnæus, used to say that animals _grow_, _live_,
and _feel_; plants _grow_ and _live_; and minerals _grow_.

Animals are here defined to enjoy _three_ conditions of existence;
plants _two_ conditions; and minerals _one_ condition.

This definition has, in latter days, been held to be unsatisfactory,
since there _are a few plants_ that are _supposed to feel_, and _a
few animals_ that are supposed to have even _less feeling_ than the
_sensitive plants_ alluded to.

The concise definition by Linnæus, nevertheless, is true, as far as
regards a _vast majority_ of the bodies constituting the three great
kingdoms of nature. And it may be sufficient to say that

_Animals_--grow, live, feel, and move.

_Plants_--grow and live.

_Minerals_--grow, by the addition of particles of inorganic matter.

     If we now state the few exceptions that are admitted to this
     definition, we shall bring the explanation as near to the truth,
     as the present state of knowledge will permit.

[Verse: "And God said, Behold, I have given you every herb bearing
seed, which is upon the face of all the earth, and every tree, in the
which is the fruit of a tree, yielding seed; to you it shall be for
meat."--GENESIS I.]

1141. _Why is it understood that some plants feel?_

Because the _sensitive plant_ closes its leaves on being touched; the
_Venus's fly trap_ closes its leaves upon flies that alight upon them;
others _close_ upon the approach of rain, and at sunset, and _open_ at
sunrise, and turn towards the sun during its daily transit.

1142. _Why is it understood that some plants move?_

Because certain _sea-weeds_ throw off undeveloped young plants, which
move through the water by the aid of fine _cilia_, or muscular hairs,
until they find a suitable place upon which to attach themselves.

The roots of plants will penetrate through the ground in the direction
of water, and of favourable soil.

1143. _Of what elementary substances are plants composed?_

Of carbon, oxygen, hydrogen, and nitrogen.

1144. _Whence do plants derive those substances?_

From the air, the earth, and water.

1145. _How do plants obtain carbon?_

They obtain it chiefly from the air, in the form of _carbonic acid
gas_. The carbon, of the carbonic acid gas, which is thrown out by
the breath of animals, and by other processes in nature, is _absorbed
by the leaves of plants_, and the _oxygen_ which had united with the
carbon to form the _carbonic acid gas_, is again set free for the use
of animals.

1146. _How do plants obtain oxygen?_

They obtain it from the _atmospheric air_. But as they do not require
a large amount of oxygen for their own use, _they throw off the amount
which is in excess_, after having separated it from the other elements
with which it was combined when taken up by them. From the humble blade
of grass, to the stately tree of the forest, plants operate to purify
the air, and to correct and counteract the corruption of the air, by
the myriads of animals inhabiting the earth.

     It has been generally stated that plants in rooms purify the air
     by absorbing carbonic acid _by day_, and releasing a part of the
     oxygen; but that, as the presence of light is necessary to produce
     this action, they do not restore oxygen to the air, by night, but,
     on the contrary, give off carbonic acid gas. Therefore it has been
     stated that plants in rooms by night are unhealthy. Mr. Robert
     Hunt, one of the ablest chemists of the present time, makes the
     following remarks upon this subject in his "Poetry of Science:"--

[Verse: "The heavens declare the glory of God: and the firmament
showeth his handy work. Day unto day uttereth speech, and night unto
night showeth knowledge."--PSALM XIX.]

     "The power of decomposing carbonic acid is a vital function
     which belongs to the leaves and bark. It has been stated, on the
     authority of Leibig, that during the night the plant acts only
     as a mere bundle of fibres--that it allows of the circulation of
     carbonic acid and its evaporation, unchanged. In his eagerness to
     support his chemical hypothesis of respiration, the able chemist
     neglected to enquire if this was absolutely correct. The healthy
     plant never ceases to decompose carbonic acid during one moment of
     its existence; but during the night, when the excitement of light
     is removed, and the plant reposes, its vital powers are at their
     minimum of action, and a much less quantity is decomposed than
     when a stimulating sun, by the action of its rays, is compelling
     the exertion of every vital function."

     In hot, swampy countries, where vegetation is very rapid, and
     the soil loaded with decomposing carbonic matter, the plants
     absorb more carbonic acid than they require, and they _then_
     evolve carbonic acid gas from their leaves. Hence such climates
     as the West Indies are injurious to _life_, though favourable to
     _vegetation_.

1147. _How do plants obtain hydrogen?_

They obtain _hydrogen_ in combination with _oxygen_ in water, and with
_nitrogen_, in the form of _ammonia_, as which it exists in animal
manures.

1148. _How do plants obtain nitrogen?_

From the _atmospheric air_, and from the _soil_, in which it is
combined with other elements.

1149. _How do plants apply these elements to the formation of their own
structures?_

When those substances which form the food of plants are absorbed,
either by their leaves or their roots, they are converted, with the aid
of water, into a _nutritive sap_, which answers the same purposes in
_plants_ as _blood_ does in _animals_.

1150. _How is the nutritive sap applied to the growth and enlargement
of the plant?_

Every seed contains a small amount of nutrition, sufficient for the
sustentation of the _germ of the plant_, until those vessels are
formed, by which the nutritive elements can be absorbed and used for
the further development of the living structure.

The earth, penetrated by the sun's rays, warms the sleeping germ, and
quickens it into life. For a short time the germ lives upon the seed,
which, moistened and warmed by the soil, yields a kind of glutinous
sap, out of which the first members of the plant are formed. And
then the tender leaf, looking up to the sky, and the slender rootlet
penetrating the soil, begin to draw their sustenance from the vast
stores of nature.

[Verse: "He causeth the grass to grow for the cattle, and herb
for the service of man: that he may bring forth food out of the
earth."--PSALM CIV.]

1151. _Of what do vegetable structures consist?_

Of _membranes_, or thin tissues, which, being variously arranged, form
cells, tubes, air passages, &c. Of _fibres_, which form a stronger
kind of membrane, and which is variously applied to the production of
the organs of the plants. And of _organs_, formed by those elementary
substances, by which the plants absorb, secrete, and grow, and fulfil
the conditions of their existence.

1152. _Why are seeds generally enveloped in hard cases?_

Because the covering of the seed, like the shell of an egg, is designed
_to preserve the germ_ within from the influence of external agencies,
until the time for development has arrived, and the conditions of
germination are fulfilled.

1153. _Why does a seed throw out a root, before it forms a leaf?_

Because moisture, which the root absorbs from the earth, is necessary
to enable the germ _to use the nutrition which the seed itself
contains_, and out of which the leaf must be eliminated. Moisture forms
a kind of gluten, in which the starch of the seed is dissolved, and
converted into sugar, the sugar into carbonaceous sap, and the sap into
cellular tissue and woody fibre, as the leaves present themselves to
the influence of the air and light.

1154. _Why does a plant grow?_

Because, as soon as membranes and vessels are organised in the young
germ, the nutritive fluid, formed by its first organs, _begins to move
through the fine structures_, and from that time the plant commences
to incorporate with its own substance the elements with which it is
surrounded, that are suitable to its development.

[Verse: "Can the rush grow up without mire? can the flag grow
without water? Whilst it is yet in his greenness, and not cut down, it
withereth before any other herb."--JOB VIII.]




CHAPTER LIX.


1155. _Why, if we break the stem of a hyacinth, do we see a glutinous
fluid exude?_

Because, by breaking the stem, we rupture the vessels of the plant, and
cause the nutritive fluid to escape. The sap of the plant is _analogous
to the blood of man_, and the vessels, to the arteries and veins of the
animal body.

1156. _Why, if we split the petal of a tulip, do we see cells
containing matter of various colours?_

Because, by splitting the petal of the flower, we disclose the anatomy
of its structure, and bring to view those cells, or organs, of the
vegetable body, by which _the different colouring matters are secreted_.

1157. _Why, if we break a pea-shell across, do we discover a
transparent membrane which may be removed from the green cells
underneath?_

Because we separate from the cellular, or fleshy part of the shell, the
membrane, _which forms the epidermis_, and answers to the skin of the
animal body.

1158. _Why, if we cut through a cabbage stump, do we find an outer coat
of woody fibre, and an inner substance of cellular matter?_

Because the woody fibre _forms a kind of skeleton_, which supports
the internal stricture of the plant, and gives form and character to
its organisation. The woody fibre of plants is analogous to the bony
structure of animal bodies.

1159. _Why, if we cut across the stem of a plant do we see numerous
tubes arranged in parallel lines?_

Because we thereby bring to view _the vessels formed by the membranes
and fibres_ of the vegetable body, for the transmission of the fluids,
by which the structure is sustained.

[Verse: "It was planted in a good soil by great waters, that it
might bring forth branches, and that it might bear fruit, that it might
be a goodly vine."--EZEKIEL XVII.]

     Skeleton leaves, and seed vessels of plants, form exceedingly
     interesting objects, and serve to illustrate the wonderful
     structure of plants. With patience and care, they may be produced
     by any person, and will afford an interesting occupation. The
     leaves should be gathered when they are in perfection--that is,
     when some of the earliest leaves begin to fall from the trees.
     Select perfect leaves, taking care that they are not broken, or
     injured by insects. Lay them in pans of _rain water_, and expose
     them to the air to undergo decomposition. Renew the water from
     time to time, taking care not to damage the leaves. They need
     not be examined more than once a week, and then only to see that
     the water is sufficient to cover them. Give them sufficient time
     for their soft parts to become decomposed, then take them out,
     and laying them on a white plate with a little water, wash away
     carefully, with a camel-hair pencil, the green matter that clings
     to the fibres. The chief requirement is _patience_ on the part
     of the operator, to allow the leaves and seed vessels sufficient
     time to decompose. Some leaves will take a few weeks, and others
     a few months, but a large panful may be put to decompose at the
     same time, and there will always be some ready for the process
     of cleansing. When they are thoroughly cleaned, they should be
     bleached, by steeping for a short time in a weak solution of
     chloride of lime. They should then be dried, and either pressed
     flat, or arranged in bouquets for preservation under glass shades.
     The result will amply reward the perseverance of the operator.

1160. _Why are clayey soils unfavourable to vegetation?_

Because the soil is _too close and adhesive_ to allow of the free
passage of air or water to the roots of the plants; it also obstructs
the expansion of the fibres of the roots.

1161. _Why are sandy soils unfavourable to vegetation?_

Because they consist of particles that have _too little adhesion to
each other_; they do not retain sufficient moisture for the nourishment
of the plants; and they allow too much solar heat to pass to the roots.

1162. _Why are chalk soils unfavourable to vegetation?_

Because they do not absorb the solar rays, _and are therefore cold to
the roots of plants_.

1163. _Why are mixed soils favourable to vegetation?_

Because they contain the _elements of nutrition_ essential to the
development of the vegetables, and the plants absorb from them those
constituents which are necessary to their growth.

1164. _Why do farmers sow different crops in rotation?_

Because every plant takes something from the soil, and gives something
back; but all kinds of plants do not absorb nor restore the elements in
the same proportions. Therefore a succession of crops of one kind would
soon impoverish the soil; but a succession of crops of different kinds
will compensate the soil, in some degree, for the nourishment withdrawn.

[Verse: "He watereth the hills from his chambers; the earth is
satisfied with the fruit of thy works."--PSALM CIV.]

1165. _Why do farmers manure their lands?_

Because, as soils vary, and crops impoverish the soils, the farmer
employs manure _to restore fertility_, and to _adapt the soils to the
wants of the plants_ he desires to cultivate.

     It is remarkable that Nature herself points out to man the
     necessity for changing the succession of vegetable growths.

     When plants have exhausted the soil upon which they grow, they
     will push their roots far in search of sustenance, and in time
     migrate to a new soil, while other plants will spring up and
     thrive upon the area vacated. When a forest in North America is
     destroyed by fire, the trees that grow afterwards are unlike
     those that the fire consumed, and evidently arise from seeds that
     have long lain buried in the earth, waiting the time when the
     ascendancy of the reigning order of plants should cease.

1166. _Why are grasses so widely diffused throughout nature?_

Because they form the _food_ of a very large portion of the animal
kingdom. They have therefore been abundantly provided. No spot of
earth is allowed to remain idle long. When the foot of man ceases to
tread down the path, grass immediately begins to appear; and by its
universality and the hardihood of its nature, it clothes the earth as
with a carpet.

     Many grasses, whose leaves are so dry and withered that the
     plants appear dead, revive and renew their existence in the
     spring by pushing forth new leaves from the bosom of the former
     ones.--_Withering's Botany._

     Grasses are Nature's care. With these she clothes the earth;
     with these she sustains its inhabitants. Cattle feed upon their
     leaves; birds upon their smaller seeds; men upon the larger;
     for, few readers need be told that the plants which produce our
     bread-corn, belong to this class. In those tribes which are
     more generally considered as grasses, their extraordinary means
     and powers of preservation and increase, their hardiness, their
     almost unconquerable disposition to spread, their faculties of
     reviviscence, coincide with the intention of nature concerning
     them. They thrive under a treatment by which other plants are
     destroyed. The more their leaves are consumed, the more their
     roots increase. The more they are trampled upon, the thicker they
     grow. Many of the seemingly dry and dead leaves of grasses revive,
     and renew their verdure in the spring. In lofty mountains, where
     the summer heats are not sufficient to ripen the seeds, grasses
     abound which are viviparous, and consequently able to propagate
     themselves without seed. It is an observation, likewise, which
     has often been made, that herbivorous animals attach themselves
     to the leaves of grasses; and, if at liberty in their pastures to
     range and choose, leave untouched the straws which support the
     flowers.--_Paley._

[Verse: "For the earth bringeth forth fruit of herself; first the
blade, then the ear, after that the full ear in the corn."--MARK V.]




CHAPTER LX.


1167. _Why do some plants droop, and turn to the earth after sunset?_

Because, when the warmth of the son's rays is withdrawn, they turn
downwards, and _receive the warmth of the earth by radiation_.

1167. _Why does the young ear of corn first appear enfolded in two green
leaves?_

Because the light and air would _act too powerfully for the young ear_;
two leaves therefore join, and embrace the ear, and protect it until it
has acquired strength, when they divide, and leave the ear to swell and
ripen.

1168. _Why are the seeds of plants usually formed within the corollas
of flowers?_

Because the petals of the flowers, surrounding the seeds, _afford them
protection until they are ripened_, when the flower dies, and the
petals fall to the ground.

1169. _Why does the flower of the poppy turn down during the early
formation of seed?_

Because the heat would probably be too great for the seed in its
early stage. The plant is therefore provided with a curious _curve in
its stalk_, which turns the flower downward. But when the seeds are
prepared for ripening, _the stalk erects itself_, and the seeds are
then presented to the ripening influences of the sun.

1170. _Why have plants of the pea tribe, a folding blossom called the
"boat," or "keel?"_

Because, within that blossom the pea is formed, and the shape of the
blossom is exactly suited to that of the pea which is formed therein.
The blossom is itself protected by external petals; and when the wind
blows, and threatens to destroy the parts upon which the seeds depend,
the plants _turn their backs to the wind_, and shelter the seed.

[Verse: "The fruit of the righteous is a tree of life; and he that
winneth souls is wise."--PROVERBS XI.]

1171. _Why are the leaf buds enclosed in scales which fall off as the
leaf opens?_

Because the scales _serve as a shelter_ to the tender structure of the
young leaf. The scales are rudimentary leaves, formed at the end of the
previous season, and which, being undeveloped then, serve to guard the
young leaves of the future year.

     In trees, especially those which are natives of colder climates,
     this point is taken up earlier. Many of these trees (observe
     in particular the _ash_ and the _horse-chestnut_) produce the
     embryos of the leaves and flowers in one year, and bring them to
     perfection the following. There is a winter therefore to be gotten
     over. Now what we are to remark is, how nature has prepared for
     the trials and severities of that season. These tender embryos
     are, in the first place wrapped up with a compactness, which
     no art can imitate; in which state they compose what we call
     the bud. This is not all. The bud itself is enclosed in scales;
     which scales are formed from the remains of past leaves, and
     the rudiments of future ones. Neither is this the whole. In the
     coldest climates, a third preservative is added, by the bud
     having a _coat_ of gum or resin, which, being congealed, resists
     the strongest frosts. On the approach of warm weather this gum
     is softened, and ceases to be an hindrance to the expansion of
     the leaves and flowers. All this care is part of that system
     of provisions which has for its object and consummation, the
     production and perfecting of the seeds.--_Paley._

1172. _Why are the seeds of many plants enclosed in a rich juice, or
pulp?_

Because the matter by which the seed is surrounded, as well as being
intended for the _nourishment and care of the seed_, is designed for
the use of man and of animals, by whom the seed is set free to take its
place in the earth.

     By virtue of this process, so necessary, but so diversified, we
     have the seed, at length, in stone-fruits and nuts, incased in
     a strong shell, the shell itself enclosed in a pulp or husk, by
     which the seed within is, or hath been, fed; or, more generally
     (as in grapes, oranges, and the numerous kinds of berries),
     plunged overhead in a glutinous syrup, contained within a skin or
     bladder; at other times (as in apples and pears) embedded in the
     heart of a firm fleshy substance; or (as in strawberries) pricked
     into the surface of a soft pulp.

     These and many more varieties exist in what we call _fruits_.
     In pulse, and grain, and grasses; seeds (as in the pea tribe)
     regularly disposed in parchment pods, which, though soft and
     membranous, completely exclude the wet even in the heaviest
     rains; the pod also, not seldom, (as in the bean), lined with
     a fine down; at other times (as in the senna) distended like a
     blown bladder; or we have the seed enveloped in wool (as in the
     cotton-plant), lodged (as in pines) between the hard and compact
     scales of a cone, or barricadoed (as in the artichoke and thistle)
     with spikes and prickles; in mushrooms, placed under a pent-house;
     in ferns, within slits in the back part of the leaf; or (which
     is the most general organisation of all) we find them covered by
     strong, close tunicles, and attached to the stem according to an
     order appropriated to each plant, as is seen in the several kinds
     of grains and of grasses.

[Verse: "And I will send grass in thy fields for thy cattle, that
thou mayest eat, and be full."--DEUTERONOMY XI.]

     In which enumeration, what we have first to notice is, unity of
     purpose under variety of expedients. Nothing can be more _single_
     than the design; more _diversified_ than the means. Pellicles,
     shells, pulps, pods, husks, skin, scales armed with thorns, are
     all employed in prosecuting the same intention. Secondly; we may
     observe, that in all these cases, the purpose is fulfilled within
     a just and _limited_ degree. We can perceive, that if the seeds
     of plants were more strongly guarded than they are, their greater
     security would interfere with other uses. Many species of animals
     would suffer, and many perish, if they could not obtain access
     to them. The plant would overrun the soil; or the seed be wasted
     for want of room to sow itself. It is, sometimes, as necessary to
     destroy particular species of plants, as it is, at other times,
     to encourage their growth. Here, as in many cases, a balance is
     to be maintained between opposite uses. The provisions for the
     presentation of seeds appear to be directed, chiefly against
     the inconstancy of the elements, or the sweeping destruction of
     inclement seasons. The depredation of animals, and the injuries
     of accidental violence, are allowed for in the abundance of the
     increase. The result is, that out of the many thousand different
     plants which cover the earth, not a single species, perhaps, has
     been lost since the creation.

     When nature has perfected her seeds, her next care is to disperse
     them. The seed cannot answer its purpose, while it remains
     confined in the capsule. After the seeds therefore are ripened,
     the pericarpium opens to let them out, and the opening is not
     like an accidental bursting, but for the most part, is according
     to a certain rule in each plant. What I have always thought very
     extraordinary; nuts and shells, which we can hardly crack with
     our teeth, divide and make way for the little tender sprout
     which proceeds from the kernel. Handling the nut, I could hardly
     conceive how the plantule was ever to get out of it. There are
     cases, it is said, in which the seed-vessel, by an elastic jerk,
     at the moment of its explosion, casts the seeds to a distance.
     We all, however, know, that many seeds (those of most composite
     flowers, as of the thistle, dandelion, &c.) are endowed with what
     are not improperly called _wings_; that is, downy appendages,
     by which they are enabled to float in the air, and are carried
     oftentimes by the wind to great distances from the plant which
     produces them. It is the swelling also of this downy tuft within
     the seed-vessel that seems to overcome the resistance of its
     coats, and to open a passage for the seed to escape.

     But the _constitution_ of seeds is still more admirable than
     either their preservation or their dispersion. In the body of the
     seed of every species of plant, or nearly of every one, provision
     is made for two grand purposes: first, for the safety of the
     _germ_; secondly, for the temporary support of the future plant.
     The sprout, as folded up in the seed, is delicate and brittle
     beyond any other substance. It cannot be touched without being
     broken.

     Yet in beans, peas, grass-seeds, grain, fruits, it is so fenced
     on all sides, so shut up and protected, that whilst the seed
     itself is rudely handled, tossed into sacks, shovelled into heaps,
     the sacred particle, the miniature plant remains unhurt. It is
     wonderful, also, how long many kinds of seeds, by the help of
     their integuments, and perhaps of their oils, stand out against
     decay. A grain of mustard-seed has been known to lie in the earth
     for a hundred years; and as soon as it had acquired a favourable
     situation, to shoot as vigorously as if just gathered from the
     plant. Then, as to the second point, the temporary support of
     the future plant, the matter stands thus. In grain, and pulse,
     and kernels, and pipins, the germ composes a very small part
     of the seed. The rest consists of a nutritious substance, from
     which the sprout draws its aliment for some considerable time
     after it is put forth; viz., until the fibres, shot out from the
     other end of the seed, are able to imbibe juices from the earth,
     in a sufficient quantity for its demand. It is owing to this
     constitution that we see seeds sprout, and the sprouts make a
     considerable progress, without any earth at all.

[Verse: "Say not ye, There are four months, and then cometh harvest?
behold, I say unto you, Lift up your eyes, and look on the fields; for
they are white already to harvest."--JOHN IV.]

     From the conformation of fruits alone, one might be led, even
     without experience, to suppose, that part of this provision
     was destined for the utilities of animals. As limited to the
     plant, the provision itself seems to go beyond its object. The
     flesh of an apple, the pulp of an orange, the meat of a plum,
     the fatness of the olive, appear to be _more_ than sufficient
     for the nourishing of the seed or kernel. The event shows, that
     this redundancy, if it be one, ministers to the support and
     gratification of animal natures; and when we observe a provision
     to be more than sufficient for one purpose, yet wanted for another
     purpose, it is not unfair to conclude that both purposes were
     contemplated together.--_Paley._

1173. _Why have climbing plants tough curly tendrils?_

Because, _having no woody stalks of their own_ to support them, they
require to take hold of surrounding objects, and raise themselves from
the ground by climbing. Their spiral tendrils are, therefore, so many
hands, assisting them to rise from the earth.

1174. _Why does the pea put forth tendrils, and the bean not?_

Because the bean has in its stalk _sufficient woody fibre to support
itself_, but the pea has not. We do not know a single tree or shrub
having a firm strong stem sufficient for its support which is _also_
supplied with tendrils.

1175. _Why do the ears of wheat stand up by day, and turn down by
night?_

Because, when the ear is becoming ripe, the cold dew falling into the
ear, might _induce blight_; the ears therefore turn down to the earth,
and _receive warmth by radiation_.

1176. _Why have grasses, corn, canes, &c., joints, or knots in their
stalks?_

Because a long hollow stem would be liable to bend and break. But the
joints are so many points where the fibres are bound together, and the
structure _greatly strengthened_.

[Verse: "Then shall the earth yield her increase; and God, even our
own God, shall bless us."--PSALM XLVII.]


1177. _Why have the berries of the mistletoe a thick viscid juice?_

Because the mistletoe is a _parasitical_ plant, growing upon the bark
of other trees. It will not grow in the ground; its seeds are therefore
filled with an exceedingly sticky substance, which serves to attach
them to the bark of trees, to which the berries attach themselves at
once, by throwing out tough fibres; and the next year the plant grows.

[Illustration: Fig. 75.--THE MISTLETOE.]

1178. _How are the seeds of the mistletoe transferred from its own stem
to the bark of trees?_

Various birds, and particularly the _missel thrush_, feed upon the
berries. As the bird moves in pursuit of its food, the viscid berries
attach themselves to its feathers, and in this way the thrush is the
instrument which conveys the seed to the spot to which it adheres, and
from which the tree ultimately grows.

1179. _What is the circulation of the sap in plants?_

The circulation of the sap is the movement of the nutritive juices by
which the plant is sustained. There is a slow uninterrupted movement
of the sap from the root through the stems to the leaves, and downwards
from the leaves through the bark to the root.

[Verse: "For the sun is no sooner arisen with a burning heat, but it
withereth the grass, and the flower thereof falleth, and the grace of
the fashion of it perisheth: so also shall the rich man fade away in
his ways."--JAMES I.]

1180. _Why does the sap of plants thus ascend and descend?_

Because it _conveys upward_ from the ground some of the matter by which
the plant is to be nourished, and which must undergo digestion in the
leaves; and it _brings downward_ from the leaves the matters absorbed,
for the nourishment of the plant, and discharges through the root the
substances which the plant cannot use.

The movement of the sap is most active in the spring; but in the depths
of the winter it almost ceases.

     There are other motions of the sap in plants, which are called
     _special_, in distinction from the ascending and descending of
     the sap, which is called _general_, or common to all plants. The
     special movements of the sap are peculiar to certain plants, in
     some of which a fluid, full of little green cells, is found to
     have a rotatory motion; in other plants, a milky fluid is found to
     move through particular tissues of the vegetable structure.

1181. _Why are the leaves of plants green?_

Because they secrete a carbonaceous matter, named _chlorophyll_, from
which they derive their green colour.

1182. _Why are the hearts of cabbages, lettuces, &c., of a pale yellow
colour?_

Because the action of _light_ is necessary to the formation of
_chlorophyll_; and as the leaves are folded upon each other, they
exclude the light, and the green matter is not formed.

1183. _Why do leaves turn brown in the autumn?_

Because, when their power of decomposing the air declines, the _oxygen_
absorbed in the carbonic acid gas, _lodges in the leaf_, imparting to
it a red or brown colour.

1184. _Why do succulent fruits, such as gooseberries, plums, &c., taste
acid?_

Because, in the formation of juices, a considerable amount of _oxygen_
is absorbed, and the oxygen imparts acidity to the taste.

[Verse: "The earth is full of the goodness of the Lord."--PSALM
XXXIII.]

1185. _Why do ripe fruits taste sweet, and unripe fruits taste sour?_

Because the juices of the ripe fruit contain a large proportion of
_sugar_, which in the unripe fruit has not been formed.

1186. _Why do some leaves turn yellow?_

Because they retain an excess of _nitrogen_. Leaves undergoing decay
turn either yellow, red, crimson, or violet. Yellow is due to the
excess of _nitrogen_; red and crimson to various proportions of
_oxygen_; violet to a mixture of _carbon_; and green to _chlorophyll_.

1187. _Why do leaves fall off in the autumn?_

Because they have supplied for a season the natural wants of the tree.
Every part has received nutrition through the spring and summer months;
and the wants of the tree being supplied, the chief use of the leaf
ceases, and it falls to the ground to decay, and enrich the soil.

1188. _Why do plants suffer from the smoke of cities?_

Because the smoke _injures the porous structure of the leaves_, and
interferes with their free respiration.




CHAPTER LXI.


1189. _Why are vegetable productions so widely diffused?_

Because they everywhere form the _food of the animal creation_. Without
them, neither man nor beast could exist. Even the flesh-eating animals
are sustained by them, since they live by preying upon the bodies of
vegetable-eaters.

They also enrich and beautify the earth. They present the most
charming diversities of proportions and features. From the cowslip,
the primrose, and the blue-bell of our childish days, to the broad oak
under which we recline, while children gambol round us, they are all
beautiful or sublime, and eminently useful in countless ways to man.

They spread a carpet over the surface of the earth; they cling to old
ruins, and cover hard rocks, as though they would hide decay, and give
warmth to the coldness of stone. In tropical climates they supply rich
fruits full of cool and refreshing juices, and they spread out upon the
crests of tall trees those broad leaves which shelter the native from
the scorching heat of the sun.

They supply our dwellings with furniture of every kind, from the plain
deal table, to the handsome cabinet of satin or rose-wood; they afford
rich perfumes to the toilette, and luscious fruits and wines to the
desert; they charm the eye of the child in the daisied field; they
adorn the brow of the bride; they are laid in the coffin with the dead;
and, as the cypress or the willow bend over our graves, they become the
emblems of our grief.

[Verse: "The glory of the Lord shall endure for ever: the Lord shall
rejoice in his works."--PSALM CIV.]

1190. _What is mahogany?_

Mahogany is the wood of trees brought chiefly from South America and
Spain. The finest kind is imported from St. Domingo, and an inferior
kind from Honduras.

     We all know the beauty of mahogany wood. But we do not all
     know that mahogany was first employed in the repair of some of
     Sir Walter Raleigh's ships at Trinidad in 1597. The discovery
     of the beauty of its grain for furniture and cabinet work was
     accidental. Dr. Gibbons, a physician of eminence, was building
     a house in King-street, Covent-garden; his brother, captain of
     a West Indiaman, had brought over some planks of mahogany as
     ballast, and he thought that the wood might be used up in his
     brother's building, but the carpenters found the wood too hard
     for their tools, and objected to use it. Mrs. Gibbons shortly
     afterwards wanted a small box made, so the doctor called upon his
     cabinet-maker, and ordered him to make a box out of some wood
     that lay in his garden. The cabinet-maker also complained that
     the wood was too hard. But the doctor insisted upon its being
     used, as he wished to preserve it as a memento of his brother.
     When the box was completed, its fine colour and polish attracted
     much attention; and he, therefore, ordered a bureau to be made of
     it. This was done, and it presented so fine an appearance that
     the cabinet-maker invited numerous persons to see it, before it
     was sent home. Among the visitors was her Grace the Duchess of
     Buckingham, who immediately begged some of the wood from Mr.
     Gibbons, and employed the cabinet-maker to make her a bureau
     also. Mahogany from this time became a fashionable wood, and the
     cabinet-maker, who at first objected to use it, made a great
     success by its introduction.

1191. _What is rose-wood?_

Rosewood is the wood of a tree which grows in Brazil. It is, generally
speaking, too dark for large articles of furniture, but is admirably
adapted for smaller ones. It is expensive, and the hardness of the wood
renders the cost of making articles of it very high.

[Verse: "I am come up to the height of the mountains, to the sides
of Lebanon, and will cut down the tall cedars thereof, and the choice
fir trees thereof."--II. KINGS XXIII.]

     Respecting the other woods used in the manufacture of furniture,
     we have nothing special to say, except of the oak--the emblem of
     our native land. This tree yields a most useful and durable wood,
     and as it not only defends our country by supplying our "wooden
     walls," but gives to us the floors of our houses, furnishes our
     good substantial tables, and comfortable arm-chairs, it will be
     well for us to know a few facts about this celebrated tree. It is
     said that there are no less than one hundred and fifty species
     of the oak. The importance of the growth of oaks may be gathered
     from the fact, that the building of a 70-gun ship would take forty
     acres of timber. The building of a 70-gun ship is estimated to
     cost about £70,000. Oak trees attain to the age of 1,000 years.
     The oak enlarges its circumference from 10-1/2 inches to 12 inches
     in a year. The interior of a great oak at Allonville, in Normandy,
     has been converted into a place of worship. An oak at Kiddington,
     served as a village prison. A large oak at Salcey, was used as a
     cattle fold; and others have served as tanks, tombs, prisons, and
     dwelling-houses.

     The _Mammoth tree_, which is exhibiting at the Crystal Palace,
     is one of the great wonders of the vegetable creation. It is the
     grand monarch of the Californian forest, inhabiting a solitary
     district on the elevated slopes of the Sierra Nevada, at 5,000
     feet above the sea-level. From 80 to 90 trees exist, all within
     the circuit of a mile, and these varying from 250 to 320 feet in
     height, and from 10 to 20 feet in diameter. The bark is from 12 to
     15 inches in thickness; the branchlets are somewhat pendent, and
     resemble those of cypress or juniper, and it has the cones of a
     pine. Of a tree felled in 1853, 21 feet of the bark from the lower
     part of the trunk were put in the natural form as a room, which
     would contain a piano, with seats for forty persons; and on one
     occasion 150 children were admitted. The tree is reputed to have
     been above 3,000 years old; that is to say, it must have been a
     little plant when Samson was slaying the Philistines. The portion
     of the tree exhibiting at the palace is 103 feet in height, and 32
     feet in diameter at the base.

1192. _What is tea?_

Tea is the leaf of a shrub (_Thea Chinensis_). The plant usually grows
to the height of from three to six feet, and resembles in appearance
the well-known myrtle. It bears a blossom not unlike that of the common
dog-rose. The climate most congenial to it is that between the 25th and
33rd degrees of latitude. The growth of good tea prevails chiefly in
China, and is confined to a few provinces. The _green_ and _black_ teas
are mere varieties, depending upon the culture, time of gathering, mode
of drying, &c. _Coffee was used in this country before tea._ In 1664,
it is recorded, the East India Company bought 2lb. 2oz. of coffee as
a present for the king. In the year 1832, there were 101,687 licensed
tea dealers in the United Kingdom. Green tea was first used in 1715.
A dispute with America about the duty upon tea led to the American
war, out of which arose American independence. The consumption of tea
throughout the whole world is estimated at above 52,000,000 lbs., of
which the consumption of Great Britain alone amounts to 30,000,000.
(_See_ 1225).

[Verse: "Every man should eat and drink, and enjoy the good of all
his labour, it is the gift of God."--ECCLESIASTES III.]

1193. _What is coffee?_

Coffee is the berry of the coffee plant, which was a native of that
part of Arabia called Yemen, but it is now extensively cultivated in
India, Java, the West Indies, Brazil, &c. (_See_ 1224).

     The first coffee-house in London was opened in 1652, under the
     following circumstances. A Turkey merchant named Edwards, having
     brought along with him from the Levant, some bags of coffee, and a
     Greek servant who was skilful in making it, his house was thronged
     with visitors to see and taste this new beverage. Being desirous
     to gratify his friends without putting himself to inconvenience,
     he allowed his servant to open a coffee-house, and to sell coffee
     publicly.

     Here we have another illustration of the great results springing
     from trifling causes. Coffee soon became so extensively used that
     taxes were imposed upon it. In 1660 a duty of 4d. a gallon was
     imposed upon all coffee made and sold. Before 1732 the duty upon
     coffee was 2s. a pound; it was afterwards reduced to 1s. 6d.,
     at which it yielded to the revenue, for many years, £10,000 per
     annum. The duty has been gradually reduced, and the consumption
     has gone on increasing, until at last above 25,000,000 of pounds
     are consumed annually! Fancy this great result springing from a
     "friendly coffee party" that assembled in the year 1652.

1194. _What is chocolate?_

It is a cake prepared from the cocoa-nut. The nut is first roasted like
coffee, then it is reduced to powder and mixed with water, the paste is
then put into moulds and hardened. The properties are very healthful,
but its consumption is very insignificant, as compared with tea or
coffee. The cocoa tree grows chiefly in the West Indies and South
America.

1195. _What is cocoa?_

Cocoa is also a preparation from the seeds or beans of the cocoa tree.
But the best form of cocoa for family use is to obtain the beans pure,
as they are now commonly sold ready for use, and to break them and then
grind them in a large coffee mill.

1196. _What is chicory?_

Chicory is the root of the common endive, dried and roasted as coffee,
for which it is used as a substitute. Some persons prefer the flavour
of chicory admixed with coffee. But very opposite opinions prevail
respecting the qualities of chicory. We believe it to be perfectly
healthful, and attribute the prejudice that prevails against it, to its
having been used, from its cheapness, to adulterate coffee.

[Verse: "He that tilleth the land shall have plenty of bread: but he
that followeth after vain persons shall have poverty enough."--PROVERBS
XXVIII.]

1197. _What is sugar?_

Sugar is a sweet granulated substance, which may be derived from many
vegetable substances, but the chief source of which is the sugar cane.
The other chief sources that supply it are the maple, beet-root, birch,
parsnip, &c. It is extensively used all over the world. Sugar is
supposed to have been known to the ancient Jews. It was found in the
East Indies by Newcheus, Admiral of Alexander, 325 B.C. It was brought
into Europe from Asia.

     The art of sugar refining was first practised in England, in 1659,
     and sugar was first taxed by name by James II., 1685. Sugar is
     derived from the West Indies, Brazil, Surinam, Java, Mauritius,
     Bengal, Siam, the Isle de Bourbon, &c. &c. Before the introduction
     of sugar to this country, honey was the chief substance employed
     in making sweet dishes; and long after the introduction of sugar
     it was used only in the houses of the rich. The consumption in
     England in 1700 reached only 10,000 tons; in 1834 it had reached
     180,000 tons. The English took possession of the West Indies in
     1672, and in 1646 began to export sugar. In 1676 it is recorded
     that 400 vessels, averaging 150 tons, were employed in the sugar
     trade of Barbadoes. Jamaica was discovered by Columbus, and was
     occupied by the Spaniards, from whom it was taken by Cromwell, in
     1656, and has since continued in our own possession. When it was
     conquered there were only three sugar plantations upon it. But
     they rapidly increased. Until the abolition of slavery in the West
     Indies, the production of sugar was almost exclusively limited to
     slave labour. (_See_ 1226).

1198. _What is wheat?_

Wheat, rye, barley, oats, millet, and maize, all belong to the natural
order of grain-bearing plants. They all grow in a similar manner, and
all yield starch, gluten, and a certain amount of phosphates. They are
commonly spoken of as _farinaceous foods_.

[Verse: "I clothed thee also with broidered work, and shod thee with
badgers' skin, and I girded thee about with fine linen, and I covered
thee with silk."--EZEKIEL XVI.]

     From the Sacred writings we learn that unleavened bread was common
     in the days of Abraham. In the earlier periods of our own history,
     people had no other method of making bread than by roasting corn,
     and beating it in mortars, then wetting it into a kind of coarse
     cake. In 1596, rye bread and oatmeal formed a considerable part
     of the diet of servants, even in great families. In the time
     of Charles the First, barley bread was the chief food of the
     people. In many parts of England it was more the custom to make
     bread at home than at present. In 1804, there was not a single
     public baker in Manchester. In France, when the use of yeast was
     first introduced, it was deemed by the faculty of medicine to
     be so injurious to health that its use was prohibited under the
     severest penalties. Herault says that, during the siege of Paris
     by Henry the Fourth, a famine raged, and bread sold at a crown a
     pound. When this was consumed, the dried bones from the charnel
     house of the Holy Innocents were exhumed, and a kind of bread
     made therefrom. Bread-street, in London, was once a bread market.
     From the year 1266, it had been customary to regulate by law the
     price of bread in proportion to the price of wheat or flour at
     the time. This was called the assize of bread; but, in 1815, it
     was abolished. In the year 272 there was a famine in Britain so
     severe that people ate the bark of trees; forty thousand persons
     perished by famine in England in 310! In the year 450 there was a
     famine in Italy so dreadful that people ate their own children.
     A famine, commencing in England, Wales, and Scotland, in 954,
     lasted four years. A famine in England and France, in 1193, led to
     a pestilential fever, which lasted until 1195. In 1315 there was
     again a dreadful famine in England, during which people devoured
     the flesh of horses, dogs, cats, and vermin! In the year 1775,
     16,000 people died of famine in the Cape de Verds. These are only
     a few of the remarkable famines that have occurred in the course
     of history. Let us thank God that we live in times of abundance,
     when improved cultivation, the pursuit of industry, and the
     settlement of the laws, render such a calamity as a famine almost
     an impossibility.

1199. _What is cotton?_

Cotton is a species of vegetable wool, produced by the cotton shrub,
called, botanically, _Gossypium herbaceum_, of which there are numerous
varieties. It grows naturally in Asia, Africa, and America, and is
cultivated largely for purposes of commerce.

     The precise time when the cotton manufacture was introduced
     into England is unknown; but probably it was not before the
     17th century. Since then, what wonderful advances have been
     made! The cotton trade and manufacture have become a vast source
     of British industry, and of commerce between nations. It was
     some years ago calculated that the cotton manufacture yielded
     to Great Britain one thousand millions sterling. The names of
     Hargreaves, Arkwright, Crompton, Cartwright, and others, have
     become immortalised by their inventions for the improvement
     of the manufacture of cotton fabrics. Little more than half a
     century has passed since the British cotton manufactory was in its
     infancy--now it engages many millions of capital--keeps millions
     of work people employed; freights thousands of ships that are ever
     crossing and re-crossing the seas; and binds nations together
     in ties of mutual interest. The present yearly value of cotton
     manufactures in Great Britain is estimated at £34,000,000. About
     £6,044,000 of the above sum is distributed yearly among working
     people as wages.

1200. _What is silk?_

Silk, though not directly a vegetable product, is, nevertheless,
indirectly derived from the vegetable creation, since it is a thread
spun by the silk-worm from matter which the worm derives from the
_mulberry leaf_.

[Verse: "And there was a man in Maon, whose possessions were in
Carmel; and the man was very great, and he had three thousand sheep,
and a thousand goats: and he was shearing his sheep in Carmel."--I
SAMUEL XXV.]

     Silk is supplied by various parts of the world, including China,
     the East Indies, Turkey, &c., where the silk-worm has been found
     to thrive. The attempts that have been hitherto made to cultivate
     it in this country have proved unsuccessful. At Rome, in the time
     of Tiberius, a law passed the senate which, as well as prohibiting
     the wearing of massive gold jewels, also forbade the men to debase
     themselves by wearing silk. There was a time when silk was of the
     same value as gold--weight for weight--and it was thought to grow
     upon trees. It is recorded that silk mantles were worn by some
     noble ladies at a ball at Kenilworth Castle, 1286. It was first
     manufactured in England in 1604. In the reign of Elizabeth, the
     manufacture of silk in England made rapid strides. In 1666, there
     were 40,000 persons engaged in the silk trade. The silk throwsters
     of the metropolis were enrolled in a fellowship in 1562, and
     were incorporated in 1629. In 1685, a considerable impetus was
     given to the English silk manufactures. Louis the Fourteenth
     of France revoked the edict of Nantes. The edict of Nantes was
     promulgated by Henry the Fourth of France in 1598. It gave to the
     Protestants of France the free exercise of their religion. Louis
     the Fourteenth revoked this edict in 1685, and thereby drove the
     Protestants as refugees to England, Holland, and parts of Germany,
     where they established various manufactures. Many of these French
     refugees settled in Spitalfields, and there founded extensive
     manufactories, which soon rivalled those of their own country;
     and thus the intolerance of the king was justly punished. What
     important facts we see connected with the simple thread of the
     silk-worm!

1201. _What is wool?_

Wool is a kind of soft hair or coarse down, produced by various
animals, but chiefly by sheep.

     This is another of the useful productions of nature, for which
     we are indirectly indebted to the vegetable kingdom; for were it
     not for the rich pastures forming the green carpet of the earth,
     it would be impossible for man to keep large flocks of sheep for
     the production of wool. Wool, like the hair of most animals,
     completes its growth in a year, and then exhibits a tendency to
     fall off. For the production of wool in England and Wales it has
     been estimated that there are no less than 27,000,000 sheep and
     lambs; and, in Great Britain and Ireland, the total number is
     estimated at 82,000,000. Wool was not manufactured in any quantity
     in England until 1331, when the weaving of it was introduced by
     John Kempe and other artizans from Flanders. The exportation or
     non-exportation of wool has from time to time formed a vexed
     subject for legislators. Woollen clothes were made an article of
     commerce in the reign of Julius Cæsar. They were made in England
     prior to 1200. Blankets were first made in England in 1340.
     The art of dyeing wools was first introduced into England in
     1608. The annual value of the raw material in wool is set down
     at £6,000,000; the wages of workmen engaged in the wool trade,
     £9,600,000. The number of people employed is said to be 500,000.

1202. _What is starch?_

Starch is one of the most useful products of the vegetable kingdom. As
a rule, _a vegetable, if nutritious at all, is so according to the
amount of starch which it contains_. It is most abundantly found in the
seeds of plants, and especially in the _wheat_ tribe.

It is also met with in the cellular tissues of plants, and especially
in such underground stems as the _potatoe_, _carrot_, _turnip_, _&c._,
and the stems of the _sago-palm_ fig, &c. It is also found in the
_bark_ of some trees.

[Verse: "Every good gift and every perfect gift is from above, and
cometh down from the Father of lights, with whom is no variableness,
neither shadow of turning."--JAMES I.]

1203. _Why is the horse chestnut, though containing a great quantity of
starch, unfit for food?_

Because (like many other vegetable productions) it contains with the
starch an _acrid juice_, which renders it unhealthy; and although the
juice can be separated from the starch, the process is too expensive to
be made generally available.

     The starch which is used for domestic purposes is an artificial
     preparation, and does not properly represent the starch of
     nutrition. A better idea of it is afforded by _the meal of a
     flowery potatoe_. The starch used by laundresses is frequently
     prepared from diseased potatoes. This does not impair the quality
     of the starch, for the purposes of the laundress, and the reason
     why potatoes that are diseased are thus applied is, that it is
     one method of saving some part of their value. The finest kinds
     of starch are prepared from rice. It is prepared by breaking the
     pulp, and disengaging the starch from the cells; and it is then
     put through other processes to remove the fragments of the broken
     cells. But in the flowery meal of the potatoe, the starch cell may
     be seen entire.




CHAPTER LXII.


1204. _What are vegetable oils and fats?_

Vegetable oils and fats constitute, next to starch and sugar, the most
important secretion of the vegetable creation. There are very few
plants from which some amount of oil cannot be obtained; and those
which are famed for yielding it owe their celebrity rather to the
abundance that they yield, and the peculiar qualities of their oil,
than to the secretion of oil being rare--for probably there is no plant
without it.

Oil is most commonly found in seeds, as _rape-seed_, _linseed_,
&c., but it is found also in leaves, as in the rose, sweet-briar,
peppermint, &c., where its presence may be recognised by the
distinguishing perfume; and it is also found in the wood of a few
trees, such as the sassafras and the sandal-wood; the bark frequently
yields an oily secretion.

[Verse: "Ointment and perfume rejoice the heart; so doth the
sweetness of a man's friend by hearty counsel."--PROVERBS XXVII.]

     The London and North Western Railway Company alone use about
     50,000 gallons of oil yearly.

1205. _Why are fat and oil found most abundantly in the bodies of
animals in cold climates_?

Because they contribute to keep the _bodies of animals warm_, not only
by their non-conducting property _keeping in_ the heat of the animals,
but by supplying _carbon_ abundantly to combine with _oxygen_ during
respiration, and thereby developing _animal heat_.

1206. _Why are oil and fat-forming trees found most abundantly in hot
climates?_

Because, in hot countries, the formation of large quantities of fat
in animal bodies would oppress living creatures with heat; fats
and oils are, therefore, produced in those countries chiefly by
vegetables, and are used externally by the Asiatics and Africans as an
_external_ unction for _cooling the skin_, and as _perfumes_ which give
inspiriting properties to the air, rendered oppressive by excess of
heat.

1207. _Why are succulent fruits most abundant in tropical climates?_

Because they are rendered necessary in those climates by the _excessive
heat_, and are found to have a most beneficial effect in cooling,
purifying the blood of the inhabitants of tropical countries; while
the grandeur of their foliage, and the richness of their flowers, are
in perfect keeping with the intensity of light and heat, and serve, by
throwing dense shades over the earth, to cool its surface, and to offer
to living creatures a pleasant retreat from the rays of the burning sun.

     The following sketch of _Botanical Geography_ should be read
     attentively after the reader has gone through the whole of the
     Chapters of "Reasons." The technical terms employed in the course
     of the article are nearly all explained at 1212, and should
     be committed to memory at the commencement of the perusal.
     _Mimosa_ means a sensitive plant; _concentric zones_, circular
     lines spreading from a centre; _arborescent_, resembling trees;
     _Gramineæ_, grass-like. The botanical names represent individual
     plants.

[Verse: "Blessed is the man that walketh not in the counsel of the
ungodly, nor standeth in the way of sinners, nor sitteth in the seat of
the scornful:"]

     1208. When treating of the geographical distribution of
     vegetables, we have to mark the general arrangements indicated,
     and the agencies that have evidently operated in promoting the
     diffusion of floral tribes. Vegetation occurs over the whole
     globe, therefore, under the most opposite conditions. Plants
     flourish in the bosom of the ocean as well as on land, under the
     extremes of cold and heat in polar and equatorial regions, on
     the hardest rocks and the soft alluvium of the plains, amidst
     the perpetual snow of lofty mountains, and in springs at the
     temperature of boiling water, in situations never penetrated by
     the solar rays, as the dark vaults of caverns, and the walls of
     mines, as well as freely exposed to the influences of light and
     air. But these diverse circumstances have different species and
     genera. There is only one state which seems fatal to the existence
     of vegetable life--the entire absence of humidity.

     1209. By species we understand so many individuals as intimately
     resemble each other in appearance and properties, and agree in all
     their permanent characters, which are founded in the immutable
     laws of creation. An established species may frequently exhibit
     new varieties, depending upon local and accidental causes,
     but these are imperfectly, or for a limited time, if at all,
     perpetuated.

     1210. A genus comprises one or more species similar to each other,
     but essentially differing in formation, nature, and in many
     adventitious qualities from other plants. A tribe, family, group,
     or order, comprises several genera.

     1211. The known number of species in the vegetable kingdom has
     been gradually enlarged by the progress of maritime and inland
     discovery; but owing to great districts of the globe not having
     yet been explored by the botanist, the interior of Africa, and
     Australia, with sections of America, Asia, and Oceanica, it is
     impossible to state the exact amount. The successive augmentation
     of the catalogue appears from the numbers below:

                                                   Species.
         Theophrastus                                  500
         Pliny                                       1,000
         Greek, Roman, and Arabian botanists         1,400
         Bauhin                                      6,000
         Linnæus                                     8,800
         Persoon                                    27,000
         Humboldt and Brown                         38,000
         De Candolle                                56,000
         Lindley                                    86,000
         Hinds                                      89,000

     1212. Vegetable forms are divided into three great classes
     which differ materially in their structure:--1. Cryptogamous
     plants--those which have no flowers, properly so called, mosses,
     lichens, fungi, and ferns: as distinguished from those which
     are phænogamous, or flower-bearing, to which the two following
     classes belong. 2. Endogenous plants, which have stems increasing
     from within, also called Monocotyledons, from having only one
     seed-lobe, as the numerous grasses, lilies, and the palm family.
     3. Exogenous plants, which have stems growing by additions from
     without, also called Dicoteledons, from the seed consisting of two
     lobes, the most perfect, beautiful, and numerous class, embracing
     the forest trees, and most flowering shrubs and herbs.

     1213. The exogens furnish examples of gigantic size, and great
     longevity. In South America on the banks of the Atabapo, Humboldt
     measured a _Bombax caiba_ more than 120 feet high, and 15 in
     diameter; and near Cumana, he found the _Zamang del Guayra_, a
     species of mimosa, the pendant branches of the hemispherical head
     having a circumference of upwards of 600 feet. The _Adansonia_, or
     baobab of Senegal, though attaining no great height, rarely more
     than fifty feet, has a trunk with a diameter sometimes amounting
     to 34 feet; while the _Pinus Lambertiana_, growing singly on the
     plains west of the Rocky Mountains, has been found 250 feet high,
     60 feet in circumference at the base, 4-1/2 feet in girth at the
     height of 190 feet, yielding cones 11 inches round, and 16 long.
     The _Ficus Indicus_, or banian tree, sending out shoots from its
     horizontal branches, which reaching the ground take root, and form
     new stems till a single tree multiplies almost to a forest, has
     been observed covering an area of 1700 square yards.

[Verse: "He shall be like a tree planted by the rivers of water,
that bringeth forth his fruit in season: his leaf also shall not
wither; and whatsoever he doeth shall prosper."--PSALM I.]

     1214. From the number of concentric zones observed in a transverse
     section of the stems De Caudolle advances proof of the following
     ages:

         Elm                                    335 years.
         Cypress                          about 350   "
         Cheirostemon                       "   400   "
         Ivy                                    450   "
         Larch                                  576   "
         Orange                                 630   "
         Olive                                  700   "
         Oriental Plane                     "   720   " and upwards.
         Cedar of Lebanon                   "   800   "
         Oak                        810, 1080, 1500   "
         Lime                            1076, 1147   "
         Yew                 1214, 1458, 2588, 2880   "
         Taxodium                      4000 to 6000   "
         Baobab                                5150   "

     1215. Admitting, with Professor Henslow, that De Candolle
     overrated the ages of these trees one-third, they are examples of
     extraordinary longevity. Yew trees upwards of 700 years old remain
     at Fountains Abbey, Yorkshire, as there is historic evidence of
     their existence in the year 1133. But a yew in the churchyard of
     Darley-in-the-Dale, Derbyshire, is considered by Mr. Bowman as
     2000 years old.

     1216. The cryptogamous plants afford the most numerous examples of
     wide diffusion. A lichen indigenous in Cornwall, _sticta aurata_,
     is also a native of the West India Islands, Brazil, St Helena, and
     the Cape of Good Hope; while 38 lichens and 28 mosses are common
     to Great Britain and Australia, though the general vegetation
     of the two districts is remarkably discordant. Some species
     of endogenous plants are also widely distributed, the _Phleum
     alpinum_ of Switzerland occurring without the slightest difference
     at the Strait of Magellan, and the quaking grasses of Europe in
     the interior of Southern Africa. But only in very few instances
     are the same species of exogenous plants met with in regions far
     apart from each other; and generally speaking, in passing from
     one country to another, we encounter a new flora; for if the same
     genera occur, the species are not identical, while in districts
     widely separated the genera are different.

     1217. The cryptogamic plants, mosses, lichens, ferns, and fungi,
     are to the whole mass of phænogamic vegetation in the following
     proportions in different districts: Equatorial latitudes, 0 deg.
     to 10 deg.; on the plains, 1-25th, on the mountains, 1-5th;
     mean latitudes, 45 deg. to 52 deg. 1/2; high latitudes, 67 deg.
     70 deg., proportion about equal. Thus the proportion of the
     flowerless vegetation to the flowering increases from the equator
     to the poles. But the family of ferns, _filices_, viewed singly,
     forms an exception to this law, decreasing as we depart from
     equinoctial countries, being 1-20th in equatorial and 1-70th in
     mean latitudes, and not found at all in the high latitudes of the
     new world.

[Verse: "To give unto them beauty for ashes, the oil of joy for
mourning, the garment of praise for the spirit of heaviness; that they
might be called Trees of righteousness, The planting of the Lord, that
he might be glorified."--ISAIAH LXI.]

     1218. In equinoctial and tropical countries, where a sufficient
     supply of moisture combines with the influence of light and heat,
     vegetation appears in all its magnitude and glory. Its lower
     orders, mosses, fungi, and confervæ, are very rare. The ferns
     are aborescent. Reeds ascend to the height of a hundred feet,
     and rigid grasses rise to forty. The forests are composed of
     majestic leafy evergreen trees bearing brilliant blossoms, their
     colours finely contrasting, scarcely any two standing together
     being of the same species. Enormous creepers climb their trunks;
     parasitical orchidæ hang in festoons from branch to branch, and
     augment the floral decoration with scarlet, purple, blue, rose,
     and golden dyes. Of plants used by man for food, or as luxuries,
     or for medicinal purposes, occurring in this region, rice,
     bananas, dates, cocoa, cacao, bread-fruit, coffee, tea, sugar,
     vanilla, Peruvian bark, pepper, cinnamon, cloves, and nutmegs, are
     either characteristic of it as principally cultivated within its
     limits, or entirely confined to them.

     1219. Rice (_Oryza-sativa_), the chief food of, perhaps, a
     third of the human race, is cultivated beyond the tropics, but
     principally within them, only where there is a plentiful supply
     of water. It has never been found wild; its native country is
     unknown; but probably southern Asia.

     1220. Bananas, or plantains (_Musa sapientum et paradisiaca_), are
     cultivated in intertropical Asia, Africa, and America. The latter
     species occur in Syria. The banana is not known in an uncultivated
     state. Its produce is enormous, estimated to be on the same space
     of ground to that of wheat, as 133 to 1, and to that of potatoes
     as 44 to 1.

     1221. Dates (_Phoenix dactylifera_), and cocoa (_Cocos nucifera_),
     belonging to the family _Palmæ_. The palms, remarkable for
     their elegant forms and importance to man, contribute more than
     any other trees to impress upon the vegetation of tropical and
     equinoctial countries its peculiar physiognomy. The date palm
     is a native of northern Africa, and is so abundant between the
     Barbary states and the Sahara, that the district has been named
     Biledul erid, the land of dates. As the desert is approached, the
     only objects that break the monotony of the landscape are the
     date palm, and the tent of the Arab. It accompanies the margin
     of the mighty desert in all its sinuosities from the shores of
     the Atlantic to the confines of Persia, and is the only vegetable
     affording subsistence to man that can grow in such an arid
     situation. The annual produce of an individual is from 150 to
     260lbs. weight of fruit. The cocoa palm furnishes annually about a
     hundred cocoa-nuts. It is spread throughout the torrid zone; but
     occurs most abundantly in the islands of the Indian archipelago.
     The family of palms is supposed to contain a thousand species,
     some of large size, forming extensive forests.

     1222. Cacao (_Theobrama cacao_), from the seeds of which
     chocolate is prepared, grows wild in central America, and is also
     extensively cultivated in Mexico, Guatemala, and on the coast of
     Cumana.

     1223. Bread-fruit tree (_Artocarpus incisa_), a native of the
     South Sea Islands, and Indian archipelago, grows also in Southern
     Asia, and has been introduced into the tropical parts of America;
     but the fruit is not equal to the banana as an article of human
     food.

[Verse: "And they returned and prepared spices and ointments; and
rested the Sabbath-day, according to the commandment."--LUKE XXIV.]

     1224. Coffee (_Coffea Arabica_). The bush has probably for its
     native region the Ethiopian Highlands, from whence it was taken
     in the fifteenth century to the Highlands of Yemen, the southern
     part of the Arabian peninsula. It has been introduced, and is
     now extensively cultivated in British India, Java, Ceylon, the
     Mauritius, Brazil, and the West Indies, but the quality is
     inferior, which makes the climate of the Mocha coffee district of
     importance, as peculiarly favourable to the plant. It grows there
     on hills described by Niebuhr as being soaked with rain every
     day from the beginning of June to the end of September, which is
     carefully collected for the purpose of irrigation during the dry
     season. Forskhal gives the following temperatures in the district:

         Boit el Fakih     March 16, 7 A.M. 76 deg.  1 P.M. 95 deg.
              "              "   18,   "    77         "    95
         Hodeida             "   18,   "    72         "    92-3/4
         Bulgosa, a village
         in the hills        "   20,   "    69-1/2     "    85-1/2

         Boit el Fakih      10 P.M. 81 deg.
              "                "    81
         Hodeida               "    78
         Bulgosa, a village
         in the hills          "    73

     1225. Tea (_Thea Chinensis_). The plant is indigenous in China,
     Japan, and Upper Assam. In the latter country, it has recently
     been found in a wild state, and is in process there of extensive
     cultivation. As the plant is hardy, its culture has very lately
     been attempted in the South of France, and apparently with
     complete success. A similar experiment on the burning plains of
     Algeria completely failed, all the plants being killed by the
     heat, notwithstanding every precaution. Tea was first introduced
     into Europe by the Dutch in 1666. The leaves of the coffee-plant
     have long been used as a substitute for tea, by the lower classes
     in Java and Sumatra; and recently, Professor Blume, of Leyden,
     exhibited samples of tea prepared from coffee-leaves, agreeing
     entirely in appearance, odour, and taste, with the genuine Chinese
     production.

     1226. Sugar-cane (_Saccharum officinaram_), a species of
     _Gramineæ_, occurs to some extent without the tropics, having been
     cultivated centuries ago in Europe, as at present scantily in the
     South of Spain. But it properly belongs to the torrid zone, and
     has for its principal districts, the Southern United States, the
     West Indies, Venezuela, Brazil, the Mauritius, British India,
     China, the Sunda and Philippine Islands. The plant was found wild
     in several parts of America on the discovery of that continent,
     and occurs in a wild state on many of the islands of the Pacific.

     1227. Vanilla (_Vanilla aromatica_), the fruit of which forms the
     well-known aromatic, grows wild principally in Mexico.

     1228. Peruvian bark (_Cinchona officinalis_), a forest tree, of
     which there are several species, furnishing the valuable medicine
     so called. It is exclusively confined to South America, and grows
     chiefly on the Andes of Loxa and Venezuela.

     1229. Pepper (_Piper nigrum_) belongs exclusively to the Malabar
     coast, where it has been found wild, Sumatra, which produces the
     greatest quantity, Borneo, the Malay peninsula, and Siam. Other
     species of _Piperaceoe_ occur in tropical America.

     1230. Cinnamon (_Laurus Cinnamomum_), a small tree yielding the
     aromatic bark, is found native only in the island of Ceylon; but
     another species occurs in Cochin China.

[Verse: "I am the true vine, and my Father is the husbandman."--JOHN
XV.]

     1231. Clove (_Myrtus caryophyllus_), an evergreen small tree, the
     dried flower-buds of which form the celebrated aromatic, grows
     naturally in the Moluccas, whence it has been conveyed to other
     tropical districts. The island of Amboyna, one of that group, is
     the principal seat of its cultivation. The lowest temperature
     there is 72 degs.; the mean temperature of the year 82 degs.

     1232. Nutmeg (_Myrstica moschata_) grows naturally in several
     islands of the eastern archipelago, but is principally cultivated
     in the Banda Isles.

     Tropical families and forms successively vanish with an increase
     of distance from the equator, and new phases of vegetation mark
     the transition from hot to temperate climates. Vividly green
     meadows, abounding with tender herbs, replace the tall rigid
     grasses which form the impenetrable jungle; and instead of forests
     composed of towering evergreen trees, woods of the deciduous
     class appear, which cast their leaves in winter, and hybernate
     in the colder season, the oak, ash, elm, maple, beech, lime,
     alder, birch, and sycamore. The cultivation of the vine becomes
     characteristic, with the perfection of the cereal grasses, and a
     larger proportion of herbaceous annuals and cryptogamic plants.

     1233. The vine (_Vitis vinifera_) is less impatient of a cold
     winter than a cool summer. Hence its northern limit, which
     coincides with lat. 47 deg. 30 min. on the west coast of France,
     rises in the interior, where, though the winters are colder, the
     summers are warmer, to lat. 49 degs., cuts the Rhine at Coblentz
     in lat. 50 deg. 20 min., and ascends to 52 deg. 31 min. in Germany.

     1234. Receding further from the equator, magnificent forests of
     the fir and pine tribe prevail, as in the central parts of Russia,
     on the southern shores of the Baltic, in Scandinavia, and North
     America. But some of the cereals are no longer cultivatable, and
     several timber-trees common to the temperate zone do not reach
     its northern limits. Gradually all ligneous vegetation disappears
     entirely as higher latitudes are approached, the woods having
     first dwindled to mere dwarfs in struggling with the elements,
     hostile to that state which nature destined them to assume. The
     limit of the forests is a sinuous line running along the extreme
     north of the old world; and extending from Hudson's Bay, lat.
     60 deg., to the Mackenzie River, lat. 68 deg., and thence to
     Behring's Strait. The dwarf birch (_Betula nana_), a mere bush, is
     the last tree found on drawing near the eternal snow of the pole.
     At the island of Hammerfest, lat. 70 deg. 40 min., near the North
     Cape, it rises to about the height of a man, in sheltered hollows
     between the mountains, its lower branches trailing on the ground,
     affording a shelter to the ptarmigan. In the polar zone, some low
     flowering annuals, saxifrages, ranunculi, gentians, chickweeds,
     and others, flourish during the brief ardent summer; a few
     perennials also accommodate themselves to the rigorous climate by
     spreading laterally, never rising higher than four or five inches
     from the ground; till finally no development of vegetable life is
     met with, but lichens, and the microscopic forms that colour the
     snow.

     1235. In Europe, wheat ceases with a line connecting Inverness in
     Scotland, lat. 58 deg., Drontheim in Norway, lat. 64 deg., and
     Petersburgh in Russia lat. 60 deg. 15 min. Oats reach a somewhat
     higher latitude. Barley and rye ascend to lat. 70 deg., but
     require a favourable aspect and season to produce a crop.

     1236. The northern limit of the growth of oak, lat. 61 deg.,
     falls short of that of wheat. The oak makes a singular leap at
     the confines of Europe and Asia, disappearing towards the Ural
     mountains. This is the case also with the wild-nut and apple. The
     oak and the wild-nut, however, re-appear suddenly in Eastern
     Asia, on the banks of the Argoun and the Amour; and the apple
     occurs again in the Aleutian Isles.

[Verse: "He hath made the earth by his power, he hath established
the world by his wisdom, and hath stretched out the heavens by his
discretion."--JEREMIAH X.]

     1237. The following are the northern limits of several trees in
     Scandinavia:

                                              Lat.
         Beech, _Fagus silvatica_             60 deg.  0 min.
         Hard Oak, _Quercus robur_            61  "    0  "
         Common Elm, _Ulmus campestris_       61  "    0  "
         Common Lime, _Tilia communis_        61  "    0  "
         Common Ash, _Fraxinus excelsior_     62  "    0  "
         Fruit trees                          63  "    0  "
         Hazel, Corylus, _avellana_           64  "    0  "
         Spruce Fir, _Abies excelsa_          67  "   40  "
         Service Tree, _Sorbus aucuparia_     70  "    0  "
         Scotch Fir, _Pinus silvestris_       70  "    0  "
         White Birch, _Betula alba_           70  "   40  "
         Dwarf Birch, _Betula nana_           71  "    0  "

     1238. Thus distinct vegetable regions are observed on passing
     from south to north through different climatic zones, defined
     as to their limits by the isothermal curves, and not by the
     parallels of latitude. Similar changes of vegetation mark a
     perpendicular transit through varying climates. A succession of
     plants appear on the tropical mountains which rise above the snow
     line, corresponding to those which are encountered in mean and
     high latitudes. The higher we ascend, the more does the number of
     the phænogamic class diminish in proportion to the cryptogamic,
     till only members of the latter family are found, whose further
     progress upward is arrested by the everlasting snow. The last
     lichen met with by Saussure on Mont Blanc, _Silene acaulis_, was
     also observed by M. Brevais in the neighbourhood of Bosekop, lat.
     69 deg. 58 min. where it was vegetating on the seashore, shaded by
     the last pines of Europe.

     1239. Isolated mountains display to the best advantage the effort
     of climatic change of vegetation.

     1240. Etna is divided into three great regions: _La Regione
     Culta_, or fertile region; _La Regione Sylvosa_, or woody region;
     _La Regione Deserta_, the bare or desert region. But each of
     these is susceptible of sub-divisions, defined by the presence of
     certain families of plants, forming seven botanical zones.

     1. The sub-tropical zone, which does not rise more than 100 feet
     above the level of the sea, is characterised by the palm, banana,
     Indian fig, sugar-cane, varieties of mimosa and acacia, which with
     us are only found in conservatories.

     2. The hilly zone, rises about 2,000 feet, characterised by the
     orange, lemon, shaddock, maize, cotton, and grape plants.

     3. The woody zone lies between the height of 2,000 and 4,000 feet,
     where the cork-tree flourishes, several kinds of oak, the maple,
     and enormous chestnuts.

     4. The zone between the height of 4,000 and 6,000 feet is
     distinguished by the beech, Scotch fir, birch, and, among small
     plants, by clover, sandwort, chickweed, dock, and plantain.

     5. The sub-alpine zone, between the elevation of 6,000 and 7,500
     feet, produces the barberry, soap-wort, toad-flax, and juniper.

     6. The zone between 7,500 and 9,000 feet, has almost all the
     plants of the preceding, with the fleshy and jagged groundsel.

[Verse: "In the mountain of the height of Israel will I plant it;
and it shall bring forth boughs, and bear fruit, and be a goodly cedar:
and under it shall dwell all fowl of every wing; in the shadow of the
branches thereof shall they dwell."--EZEKIEL XVII.]

     7. The narrow zone between 9,000 and 9,200 feet, only produces a
     few lichens, beyond which, there is complete sterility.

     1241. The Peak of Teneriffe exhibits five botanical districts,
     thus distinguished by Von Buch:

     1. The region of Africa forms, 0--1,248 feet, comprising
     palms, bananas, the sugar-cane, various species of arborescent
     _Euphorbiæ_, _Mesembryanthema_, the _Dracæna_, and other
     plants, whose naked and tortuous trunks, succulent leaves, and
     bluish-green tints, are distinctive of the vegetation of Africa.

     2. Region of Vines and Cereals, 1,248--2,748 feet, comprising also
     the olive, and the fruit-trees of Europe.

     3. Region of Laurels, 2,748--4,350 feet, including lauri of four
     species, the wild olive, an oak, the iron-tree, the arbutus, and
     other evergreens. The ivy of the Canaries and various twining
     shrubs cover the trunks of the trees, and numerous species of fern
     occur, with beautiful flowering plants.

     4. Region of the Pines, 4,350--6,270, characterised by a vast
     forest of trees resembling the Scotch fir, intermixed with juniper.

     5. Region of the Retama, 6,270--11,061 feet, a species of broom,
     which forms oases in the midst of a desert of ashes, ornamented
     with fragrant flowers, and furnishing food to the goats, which
     run wild on the Peak. A few gramineous and cryptogamic plants
     are observed higher, but the summit is entirely destitute of
     vegetation.

     1242. There are many plants which can accommodate themselves to
     the most diverse climates and localities; and therefore ascend
     from the plains close to the boundary of vegetable life on the
     highest mountains. But it is the general law in these cases for
     such plants to be singularly modified in appearance and anatomical
     structure as they ascend. The spring gentian, _Gentiana verna_,
     is one of the exceptions, which Raymond found unaltered at all
     heights in the Pyrenees.

     1243. Trees, plants, and bushes, of humbler growth, which occur
     on the plains and at great heights, are usually much smaller in
     the latter situation. The leaves, and everything green about them,
     dwindle with the increased elevation; and the pure, well defined
     green is exchanged for an ill-defined light yellow. Singular
     enough, those parts which seem most capable of resisting cold, as
     the leaves and stalks, are uniformly subjected to a diminution of
     their vital functions; while the flowers remain of the same size,
     are never deformed, and become more dense and richer in their
     colours. While the _Myosotis silvestris_ becomes stunted, its
     flowers assume an intense blue--the admiration of the traveller.
     The flowers of the pale primrose have a much deeper colour on the
     top of the Faulhorn, while the plant itself is much smaller than
     its congener on the Swiss plains. The observations of M. Parrot,
     among others, are to this effect on the flora of the Caucasus, of
     Ararat, the Swiss and Italian Alps, and the Pyrenees. The arctic
     flora is similarly distinguished.

     1244. The preceding references to different climatic states
     are, however, perfectly inadequate to explain the phenomena of
     vegetable distribution. While an analogy is often observable
     between the plants of different regions under corresponding
     circumstances of latitude, elevation, and soil, the species
     are generally found to be different; and usually the botanical
     character of countries not widely apart from each other, is
     totally different, though under the same parallels.

[Verse: "From the rising of the sun, unto the going down of the
same, the Lord's name is to be praised."--PSALM CXIII.]

     1245. Some plants are entirely confined to one side of our
     planet. The beautiful genus _Erica_, or heath, of which there are
     upwards of 300 species, occurs with breaks over a narrow surface,
     extending from a high northern latitude to the Cape of Good Hope.
     But the whole continent of America does not contain a single
     native specimen; nor has a _Poenia_ been found in it, except a
     solitary one to the west of the Rocky Mountains. On the other
     hand, the New World contains many families, as the _Cacti_, which
     are not found naturally in the Old.

     1246. Some plants occur in a single specific locality, frequently
     a contracted area, and nowhere else. The beautiful _Disa
     grandiflora_ is limited to a spot on the top of the Table Mountain
     at the Cape; and the celebrated cedar of Lebanon appears to be
     restricted in its spontaneous growth to the Syrian mountains. The
     small island of St. Helena has an indigenous flora, with a few
     exceptions different from that of the rest of the globe.

     1247. Mountain chains of no great width very commonly divide a
     totally distinct botany. There is a marked difference in the
     vegetation of the Chilian and opposite side of the Andes, though
     the climate as well as the soil is nearly the same, and the
     difference of longitude very trifling. In North America, two
     completely different classes of vegetation appear on the two sides
     of the Rocky Mountains. A variety of oaks, palms, magnolias,
     azaleas, and magnificent rhododendrons occur on the eastern side,
     all of which are unknown on the western, the region of the giant
     pine.

     1248. The distinct vegetation possessed by various parts of
     the globe, has led to its division into botanical kingdoms or
     phyto-geographical regions, named in general after the genera
     that are either peculiar to them, or predominant in them. The
     arrangement of M. Schouw, which is usually adopted, discriminates
     twenty-five great provinces of characteristic vegetation upon the
     surface of the earth.

     In constituting any portion of the globe into a phyto-geographical
     region, M. Schouw has proceeded upon the following principles:--1.
     That at least one-half of the species should be indigenous in it.
     2. That a-quarter of the genera should also be peculiar to it,
     or at least should have a decided maximum. 3. That individual
     families of plants should either be exclusively confined to the
     region, or have their maxima there.

     1249. The phenomena of botanical geography, and the facts of
     geology, are mutually illustrative. The existing dry land having
     been upheaved above the waters at different epochs, it may be
     reasonably inferred that each portion on its emergence received
     a vegetable creation in harmony with its position. The ultimate
     constitution of the general surface into different botanical
     kingdoms would hence follow, each of which has preserved its
     primitive features, while adjoining, and even far distant foci,
     have to some extent intermingled their respective products, under
     control of the natural agencies of diffusion.

     1250. The agents that involuntarily officiate in the diffusion
     of vegetable products are the atmosphere, the waters, and many
     animals.

     1. The impulsion of the atmosphere in its calmest state, is quite
     sufficient to transport to considerable distances seeds furnished
     with downy appendages or winglets, as is the case with many
     plants, with the minute sporules of cryptogamia, which are light
     as the finest powder. When ordinary breezes convey the sand-dust
     of the Sahara a thousand miles or more from the desert, it may be
     conceived that seeds, which are comparatively heavy, are borne far
     from home by the hurricane. Two Jamaica lichens, which had never
     been seen in France before, were found by De Candolle growing on
     the coast of Brittany, the offspring of sporules which had been
     swept over the Atlantic.

[Verse: "He shall come down like rain upon the mown grass, as
showers that water the earth."--PSALM LXXII.]

     2. The mountain torrent washes down into the valley the seeds
     that have accidentally fallen into it, or have been swept away
     by its overflows; and hence the plants of the High Alps occur on
     the plains of Switzerland, which are entirely wanting in France
     and Germany. Rivers answer the same purpose more extensively, and
     also the oceanic currents. The nicker-tree, one of the leguminous
     tribe, has been raised from seed borne across the Atlantic by the
     Gulf stream.

     3. Animals of the sheep and goat kinds, with the horse, deer,
     buffalo, and others, widely disperse several species of plants,
     the seeds of which, furnished with an apparatus of barbs and
     hooks, adhere to their coating. Seeds also of various kinds pass
     through the digestive organs of birds, uninjured as to their
     vitality. The little squirrel buries the acorn in the ground for
     winter provender, and sows an oak, if prevented from returning to
     the spot.

     1251. Plants capable of extended naturalisation, and serviceable
     as articles of food or luxury, have been widely disseminated by
     the human race in their migrations. The cerealia afford a striking
     example. These important grasses known to the ancients, wheat,
     barley, oats, and rye, were the gifts of the Old World to the New.
     They are also importations into Europe; but the loose reports of
     the ancients, and the diligent researches of the moderns, alike
     leave us in ignorance of their native seat. Probability points to
     the conclusion that they have spread from the neighbourhood of the
     great rivers of Western Asia, the primitive location of the human
     family; and it is not impossible that in that imperfectly explored
     district, or further east on the Tartarian table-land, some of the
     cereals may yet be found growing spontaneously. The first wheat
     sown in North America, consisted of a few grains accidentally
     found by a negro slave of Cortes, among the rice taken for the
     support of his army. In South America the first wheat was brought
     to Lima by one of the early colonists, a Spanish lady, Maria
     d'Escobar. An ecclesiastic, Jose Rixi, was the first to sow it in
     the neighbourhood of Quito.

     1252. Maize, or Indian corn (_Zea mays_), has been dispersed in
     the Old World from the New; and also a more important product, the
     potato (_Solanum tuberosum_), the use of which now extends from
     the extremity of Africa to Lapland. In Chili, the native country
     of the plant, it occurs at present in a wild state. The Spaniards
     imported it into Spain, and from thence it was communicated to
     Italy. It was first made known in England at a subsequent period
     from Virginia, having been received there from the Spanish
     colonists in South America, as it is not a native of intervening
     Mexico.

     1253. The grape-vine, so extensively spread over Europe, is
     probably not indigenous in any part of it. It chiefly owes its
     diffusion there to the Romans, who received it from the Greeks,
     to whom it most likely immediately came from the country between
     the Black and Caspian Seas. The Romans introduced most of the
     finer European fruit-trees, some from Africa, as the pomegranate,
     but the great majority from Western Asia, as the orange, fig,
     cherry, peach, apricot, apple, and pear. A variety of the plum,
     the damson, or damascene, came from the neighbourhood of Damascus
     during the Crusades. The name of the damask-rose points to the
     importation of the plant from the same quarter into Europe.

[Verse: "To every thing there is a season, and a time to every
purpose under heaven."--ECCLESIASTES III.]

     The ocean as well as the land has different botanical regions; and
     changes of the vegetation are observed with the depth analogous
     to the variations of terrestrial plants with the height. Marine
     vegetation seems to have its vertical extent determined by the
     range of light in water, which varies with the power of the sun
     and the transparency of the water.




CHAPTER LXIII.


1254. _What are vegetable gums?_

Vegetable gums are secretions of plants which are generally _soluble in
water_, and which subserve various useful purposes. _Gum Arabic_ is one
of the most important of this class of vegetable productions.

_Gutta-percha_ is an invaluable substance lately added to the list of
known vegetable productions. It is obtained by cutting the bark of
trees of the class called _Sapotacea_. Its proper name is gutta Pulo
Percha, gutta meaning gum, and Pulo Percha is the island whence it is
obtained. But gutta-percha is not, strictly speaking, a gum.

_India-rubber_ is also a vegetable secretion, improperly called elastic
gum. It is obtained from the milky juice of various trees and plants,
especially from the syringe tree, of Cayenne.

1255. _What are vegetable resins?_

_Vegetable_ resins are derived from the secretions of plants, and are
generally distinguished from gums by being _insoluble in water_, but
being soluble in spirits.

When one of these substances is soluble in either water or spirits it
is called a _gum-resin_.

1256. _What are vegetable acids?_

Vegetable acids are chiefly obtained from _fruit_; but also abundantly
from _wood_, by distillation.

[Verse: "Thou art the God that doest wonders."--PSALM LXXVII.]

1257. _What is tannin?_

Tannin is a vegetable production, obtained chiefly from the oak-bark,
and from a variety of other vegetable sources. It possesses the
peculiar chemical property which renders it valuable in tanning leather.

1258. _What is opium?_

Opium is the produce of the _poppy_, and is obtained from the seed.

1259. _What are vegetable dyes?_

Vegetable dyes are the various colours derived from the secretions of
plants, such as _indigo_, _madder_, _logwood_, _alkanet-root_, _&c._

1260. _What is silica?_

Silica is a mineral substance, commonly known as _flint_; and it is
one of the wonders of the vegetable tribes, that, although flint is
so indestructible that the strongest chemical aid is required for its
solution, plants possess the power of _dissolving and secreting_ it.
Even so delicate a structure as the wheat straw dissolves silica, and
every stalk of wheat is covered with a perfect, but inconceivably thin
coating of this substance.

     Amid all the wonders of nature which we have had occasion to
     explain, there is none more startling than that which reveals
     to our knowledge the fact that a flint stone consists of the
     mineralised bodies of animals, just as coal consists of masses
     of mineralised vegetable matter. The animals are believed to
     have been infusorial animalculæ, coated with silicous shells,
     as the wheat straw of to-day is clothed with a glassy covering
     of silica. The skeletons of animalculæ which compose flint may
     be brought under microscopic examination. Geologists have some
     difficulty in determining their opinions respecting the relation
     which these animalculæ bear to the flint stones in which they are
     found. Whether the animalculæ, in dense masses, form the flint;
     or whether the flint merely supplies a sepulchre to the countless
     millions of creatures that, ages ago, enjoyed each a separate
     and conscious existence, is a problem that may never be solved.
     And what a problem! The buried plant being disentombed, after
     having lain for ages in the bowels of the earth, gives us light
     and warmth; and the animalcule, after a sleep of ages, dissolves
     into the sap of a plant, and wraps the coat it wore, probably "in
     the beginning, when God created the heavens and the earth, and
     when the earth first brought forth living creatures," around the
     slender stalk of waving corn!

1261. _Why is silica diffused over the stems of wheat, grasses, canes,
&c.?_

Because it affords strength, density, and durability, to structures
that are very light, and which, but for this beautiful provision, would
be exceedingly perishable.

[Verse: "For in this mountain shall the hand of the Lord rest, and
Moab shall be trodden down under him, even as straw is trodden down for
the dunghill."--ISAIAH XXV.]

1262. _Why is guano a productive manure?_

Because it contains, with other suitable elements, an abundance of the
_silicous skeletons of animalculæ_.

1263. _Why does a wheat-crop greatly exhaust the soil?_

Because, as well as the _carbon, and the salts_, which form the straw
and the grain, it draws off from the soil a great amount of _silica_.

1264. _Why is straw frequently used as a manure?_

Because it gives back, with other substances, a _considerable
proportion of silica_, in that form which adapts it to the use of the
succeeding crop.

1265. _Why is the structure of herbaceous plants less consolidated than
that of woody plants?_

Because, for the most part, herbaceous plants last only _a single
year_; they, therefore, do not require the enduring qualities of plants
that have to sustain the influences of the elements for a succession of
seasons.

1266. _Why are the stalks of plants of light structure generally
cylindrical?_

Because the cylindrical form is stronger than any other; _a hollow
cylinder_, with moderately thick walls, _is stronger than a solid rod_,
containing the same amount of material.

1267. _Why do the stalks of plants become hollow?_

Because the parallel and perpendicular fibres of the stalk are
developed _more rapidly than the horizontal_. The growth of the plant,
therefore, consists of a kind of _divergence from the centre_.

1268. _Why are the stomata, or pores of leaves, generally placed on
their under surface?_

Because, being placed on the under surface, they are _shaded_ from
the action of the _sun's rays_, and so carry on the function of
respiration more actively than if subjected to direct heat; they are
also protected from the injurious _effects of dust_; and are moistened
by _evaporation from the earth's surface_.

[Verse: "The trees of the Lord are full of sap: and the cedars of
Lebanon which he hath planted."--PSALM CIV.]

1269. _Why have plants a formation of pith in their centre?_

The pith is the chief organ of nutriment, especially in the young
plant. It is the structure which first conveys fluids to, and receives
them from, the newly-formed leaf. It communicates with every branch,
leaf, bud, and flower; and also with the bark, through the _medullary
rays_, which radiate horizontally from the centre of the plant. It is
the centre of the movements of the sap which occur in the horizontal
vessels; and it holds an important influence over the life of the plant.

1270. _Why are trees covered with bark?_

Because the bark serves to protect the woody structure, and also to
give a passage to the descending sap which flows abundantly in the
spring, and out of which the woody fibre is formed. It is also, from
its peculiar nature, well fitted to endure the changes of the seasons
for many years; and from its non-conducting properties it serves to
maintain the equal temperature of the vital parts of the tree.

1271. _What is cork?_

Cork is the bark of a description of _oak-tree_, which grows in great
abundance in Spain, Italy, and France.

1272. _Why does the cork-tree release its own bark?_

Because it possesses a bark which is exceedingly _useful to man_;
and it seems, therefore, to have been the design of providence that
the tree should cast it off, to be applied to the wants of the human
family; for the cork-tree does not discharge its bark by the mere
cracking, or exfoliation, of its substance; the tree retains the bark
for a number of years, until it has attained that consistency and
thickness which renders it useful, and then the tree forms within the
bark a series of tabular cells, which _cut off the connection of the
bark with the internal structure_, after which it peels off in large
sheets.

[Verse: "And all the trees of the field shall know that I the Lord
have brought down the high tree, have exalted the low tree, have dried
up the green tree, and have made the dry tree to flourish: I the Lord
have spoken, and have done it."--EZEK. XVII.]

Man assists this evident intention of nature, by slitting the bark from
the top of the tree to its base; but even were this not done, the bark
would be cast off by the tree itself.

Another proof of design in this useful adaptation of the cork-tree is
to be found in the fact, that it thrives under treatment that would
destroy other trees. The cork-tree will endure the barking process for
_seven or eight successive years_.




CHAPTER LXIV.


1273. _Why are there curious markings in walnut, mahogany, rose-wood,
satin-wood, &c.?_

Because those markings are produced by the various _structure of the
vessels_ by which the wood is formed; and by successive zones of wood,
which indicate the periods of growth.

     The inclosure of zone within zone is owing to the mode in which
     the wood is produced, and the position in which it is deposited.
     Wood is formed by the leaves during the growing season, and
     passes down towards the root between the bark and the wood of the
     previous year (if any), or in the position in which cambium is
     effused; and, as the leaves more or less surround the whole stem,
     the new layer at length completes a zone, and perfectly encloses
     the wood of all former years. This is the explanation of the term
     _exogenous_, which is derived from two words signifying to grow
     outwardly, for the stem increases in thickness by successive
     layers on the outer side of the previously-formed wood. That this
     is the mode of growth has been abundantly proved by experiment,
     and demonstrated by accidental discoveries. Thus, if a plate of
     metal be inserted between the bark and wood, it will, in progress
     of time, become inclosed by the new wood which has overlaid them.
     So in like manner if letters be cut deeply through the bark and
     into the wood, the spaces will not be filled up from the bottom,
     but may be seen in subsequent years overlaid by new wood. A
     statement appeared in a daily paper, during the past year, to
     the effect that in cutting down a tree a cat had been discovered
     inclosed in the wood of the trunk. These facts prove that the wood
     is applied from without. Again, if a branch be stripped of its
     leaves down to a certain point, it will not grow above that point;
     and so, in like manner, if branches be stripped from one side of
     a tree, the tree will not grow on that side. If a circle of bark
     be removed from a branch above and also below a leaf, it will be
     found that increase of size will occur below, but not above that
     bud; and so, likewise, whenever a ring of bark is removed from a
     tree, the new woody fibre will not proceed from the lower but from
     the upper edge.--_Orr's Circle of the Sciences._

[Verse: "And when he saw a fig tree in the way, he came to it, and
found nothing thereon, but leaves only, and said unto it, Let no fruit
grow on thee henceforward for ever. And presently the tree withered
away."--MATTHEW XXI.]

1274. _Why have trees with large trunks a great number of leafy
branches?_

Because it is _by the leaves_ that the secretion is formed which
supplies the _woody fibre_. The number of leaves on a tree, therefore,
generally bears a relation to the size of its trunk, and the number of
its branches.

1275. _Why have poplar-trees comparatively few branches and leaves?_

Because their trunks are comparatively _small_, although they grow to a
great height.

1276. _Why had the mammoth-tree comparatively few leaves in relation to
the immense size of its bark?_

Because the woody texture of this tree (_Wellingtonea gigantea_) is
_exceedingly light and porous_. It is, in fact, lighter than cork, and,
therefore, requires less leaf-produce in its formation.

1277. _Why have oak-trees an abundance of leaves?_

Because their wood is _so dense_ that they require a larger amount of
the wood-forming secretion which is supplied by the leaves.

1278. _Why are the trunks of trees round?_

Because, generally speaking, the leaves are distributed upon branches
around the trees in every direction. They consequently send down the
wood-forming principle on all sides. When a trunk is unduly developed
on one side, it may generally be traced to the unequal distribution of
the branches.

1279. _What are exogenous stems?_

Exogenous stems are those that grow by the addition of wood _on their
outer surface_, underneath the bark.

1280. _What are endogenous stems?_

Endogenous stems are those that _grow inwardly_, from the centre. Trees
of this class, of which palms are the best example, are almost peculiar
to tropical climates.

1281. _Why do endogenous stems chiefly abound in tropical climates?_

Because, probably, the excessive heat of those climates would
interfere with the _formation of wood from the sap_ upon the outer
surface.

The vascular structure of endogenous stems lying more abundantly
towards their centre, tends to _conserve the juices_ which in hot
climates are so highly valued. Palm-wine is a delicious and cooling
beverage, and is procured from various kinds of palms, but especially
from the cocoa-nut palm. Even the fresh sap is very refreshing. The
juice is procured by cutting the tree in the upper part, and attaching
a vessel to the opening, to receive the sap. Its flow is increased by
cutting off a slice of the wood daily.

[Verse: "I have caused thee to multiply as the bud of the field, and
thou hast increased and waxen great, and thou art come to excellent
ornaments."--EZEKIEL XVI.]

1282. _Why have endogenous stems no bark?_

Because, one of the chief functions of the bark in exogenous trees,
is to _protect the sap_ from which the wood is formed on the outward
surface; and as there is no such external flow of sap in endogenous
trees, the bark is _unnecessary to them_, and is therefore withheld.
They are furnished instead with a thin cuticle.

1283. _Why do endogenous stems grow to a great height?_

Because, as the stem grows from the centre, it soon reaches that limit
of diameter _which its vascular structure is calculated to support_;
and, therefore, the wood-forming sap is deposited chiefly at the top of
the stem, causing it to grow to a considerable height.

1284. _Why do the various vegetable fruits ripen in succession?_

Because the Author of Nature has thus arranged its economy, _in order
that the wants of living creatures may be adequately provided for_.
Some vegetable productions arrive at their perfection in the spring;
others in summer; and others in autumn. Among the latter are many that
require to come slowly to maturity after they are gathered; by these
the winter season is provided for, and a surplus of the winter stock
goes to supply the natural deficiency of spring.

[Verse: "O sing unto the Lord a new made song; for he hath done
marvellous things."--PSALM XCVIII.]

1285. _Why, when seeds are sown, and germination begins, does the
leaf-germ seek the light, and the root-germ grow down into the earth?_

Because the Creator has endowed every single seed with a _vital
instinct which governs its development_. The rootlet could more easily
grow upward than downward, because of the looser earth, and of the
exciting influences of light and moisture. Yet it takes the contrary
course, leaving the leaf-germ to come up to meet the sun-light, and to
send down to the stem and roots, the matter needed for their growth.

Frequently, indeed, when seeds are thrown into the earth, their natural
position is reversed, and when the germs first start from the seed, the
_root-germ_ is directed _upward_ and the _leaf-germ downward_. What
then occurs? They each turn, and, in doing so, frequently cross each
other. Each goes to its particular duty--the duty that God appointed.




CHAPTER LXV.


1286. _Why are the seeds of plants indigestible?_

Because they are encased in a hard covering upon which the gastric
juice of animals takes no effect. This provision has been made by the
Creator, _for the preservation of seeds_, the productions of which are
so essential to animal life.

The gastric juice can dissolve any other part of the plant, even the
woody fibre, and yet upon the _seed_ it takes no effect. When, however,
the seed is _crushed_, and, thereby, the vital principle destroyed, so
that no plant can spring from it, the gastric juice acts upon it, and
it is soon dissolved.

Hence graminivorous birds are provided with gizzards _to break the
protecting coats of the grain_; and animals that feed on seeds and nuts
_strip them of their shells and husks_.

It is remarkable that in the _succulent fruits_, such as the
strawberry, the raspberry, currant, apple, orange, melon, &c., and
which, from their very nature, are likely to attract animals to use
them, and in eating which _the seeds are likely to be swallowed_, they
are fortified by a doubly-protective coating; the pips of the apple,
orange, &c., and the seeds of the strawberry and raspberry, pass
through the digestive organs, not only unharmed, but their germinating
powers are even improved by the warmth and trituration of the stomach.
Indeed, the stomachs of quadrupeds and birds have been made the
vehicles of propagating plants, and distributing them to the widest
geographical latitudes. It is even said of some seeds that they will
not germinate until they have passed through the digestive organs of an
animal.

[Verse: "And it was commanded them that they should not hurt
the grass of the earth, neither any green thing, neither any
tree."--REVELATION IX.]

1287. _Why do animals that graze, crop the tender blades of grass, but
avoid the tall stems?_

Because they are tempted by the greater sweetness and tenderness of the
young blades; and in this temptation a very important end is served;
for, by avoiding the stems that have grown up, _the animals spare the
matured plant by which seeds are borne_, and by which the supply of
food is to be continued.

1288. _Why do the eggs of butterflies lie dormant during the winter?_

Because the _coldness of the winter_ would be fatal to the life of
the young insects; and the absence of vegetation would leave the
caterpillars to _perish of starvation_, if they were developed during
the winter months.

[Illustration: Fig. 76.--CATERPILLAR FEEDING.]

1289. _Why do caterpillars appear in the spring?_

Because the increasing warmth of the sun developes the living embryo,
_at the same time that it developes the vegetable germ_. The warmth,
therefore, that calls the caterpillar from its embryo sleep, also
kindles the germinating power of the vegetable upon which it is
destined to feed. The worm awakes and finds the bountiful table of
nature spread for it.

[Verse: "Thou shalt plant vineyards, and dress them, but shalt
neither drink of the wine, nor gather the grapes: for the worms shall
eat them."--DEUTERONOMY XXVIII.]

1290. _Why does the caterpillar eat voraciously?_

Because it _grows rapidly_, and a large amount of vegetable matter
is necessary to supply the rapid growth of its animal substance.
Caterpillars in the course of a month devour 60,000 times their own
weight of aliment.

[Illustration: Fig. 77.--THE UNDER SIDE OF THE CHRYSALIS OF THE PEACOCK
BUTTERFLY.]

[Illustration: Fig. 78.--THE SAME CHRYSALIS, WITH PART OF ITS SHEATH
RAISED TO SHOW THE PARTIALLY-FORMED WINGS, &c.]

1291. _Why do caterpillars pass into the state of the chrysalis?_

Because they are thereby prepared for the new existence which they are
about to enjoy; _new organs must be perfected in them_ to adapt them to
the altered conditions of their lives.

Because, also, in the transformation of their bodies, differing
materially from the laws of existence that pertain to other creatures,
the Creator affords another illustration of his Omnipotence.

Because, also, during the stage that the insect sleeps in the
chrysalis, the flowers and their sweet juices, upon, which the fly is
to feed, are being prepared for it, just as, when it was sleeping in
the egg, the green food was being prepared for the caterpillar. When,
therefore, the beautiful fly spreads its silken wings, it finds a
_second time_ that, while it has slept, its meal has been prepared, and
it now flies away joyously to feed upon the milk and honey of beautiful
flowers which, at the time it passed into the chrysalis, had not yet
unfolded their petals.

[Verse: "For the moth shall eat them up like a garment, and the worm
shall eat them like wool: but my righteousness shall be for ever, and
my salvation from generation to generation."--ISAIAH LI.]

[Illustration: Fig. 79.--THE PEACOCK BUTTERFLY.]

Paley observes, that "the _metamorphosis_ of insects from grubs into
moths and flies, is an astonishing process. A hairy caterpillar
is transformed into a butterfly. Observe the change. We have four
beautiful wings where there were none before; a tubular proboscis, in
the place of a mouth with jaws and teeth; six long legs, instead of
fourteen feet. In another case, we see a white, smooth, soft worm,
turned into a black, hard, crustaceous beetle, with gauze wings. These,
as I said, are astonishing processes, and must require, as it should
seem, a proportionably artificial apparatus. The hypothesis which
appears to me most probable, is that, in the grub, there exists at
the same time three animals, one within another, all nourished by the
same digestion, and by a communicating circulation; but in different
stages of maturity. The latest discoveries made by naturalists, seem
to favour this supposition. The insect, already equipped with wings,
is descried under the membranes both of the worm and nymph. In some
species, the proboscis, the antennæ, the limbs, and wings of the fly,
have been observed to be folded up within the body of the caterpillar;
and with such nicety as to occupy a small space only under the two
first wings. This being so, the outermost animal, which, besides its
own proper character, serves as an integument to the other two, being
the farthest advanced, dies, as we suppose, and drops off first. The
second, the pupa or chrysalis, then offers itself to observation. This
also, in its turn, dies; its dead and brittle husk falls to pieces, and
makes way for the appearance of the fly or moth. Now, if this be the
case, or indeed whatever explication be adopted, we have a prospective
contrivance of the most curious kind; we have organisations _three
deep_; yet a vascular system, which supplies nutrition, growth, and
life, to all of them together."

[Verse: "That which the palmer-worm hath left hath the locust eaten;
and that which the locust hath left hath the canker-worm eaten; and
that which the canker-worm hath left hath the caterpillar eaten."--JOEL
I.]

Lord Brougham, in a note upon the above, does not support Paley's
view. He says "It is more than probable that the parts which are to
appear in the perfect insect do _not_ exist in the larvæ, where there
is not much difference between the larva and pupa, excepting at the
time just previous to its becoming a pupa, at which time the larva is
motionless and torpid. The caterpillar of a moth, when about to turn
into a pupa, provides for the protection of the latter state, either by
surrounding itself with a web, or by some other means. Soon after this
is accomplished, the caterpillar becomes motionless, or nearly so; it
can neither eat nor crawl. At this time, and _not before_, the parts of
the pupa are forming within the skin of the caterpillar, which may be
easily seen by dissection."

It appears to the author, however, that Paley is partially right, and
Lord Brougham totally wrong, in these remarks. When Lord Brougham
asserts that the parts of the pupa are forming within the skin of
the caterpillar at that time when the transformation begins, "and
not before, which may be easily seen by dissection," he forgets,
that although in some instances it is the first moment when, to the
human eye, the organs of the new creature _become perceptible_, that
the "_three deep_" nature which Paley attributes to the _grub_, must
really have existed _in the egg_--that the _butterfly_ originated _in
the egg_, as certainly as did the _caterpillar_, or the _chrysalis_,
and that unless that egg had possessed its three mysterious embryos,
it would have been impossible for the grub to have progressed to
the stages of transformation. No one has ever known the embryo of a
bird's egg to pass through three distinct and dissimilar states of
existence; nor has any one ever known the embryo of the butterfly's
egg to stop short at either of the stages, if the proper conditions of
its existence and development were supplied to it. _Why?_ Because the
embryo of the insect has a _threefold_ nature, while that of the bird
is _single_.

[Verse: "They shall cut down her forest, saith the Lord, though it
cannot be searched; because they are more than the grasshoppers, and
are innumerable."--JEREMIAH XLVI.]




CHAPTER LXVI.


1292. _Why does the caterpillar become torpid when passing into the
state of the chrysalis?_

Because in all probability, where the difference between the first and
the ultimate form is considerable, the organs of the insect having to
undergo great changes, it would suffer considerable pain. Torpor comes
upon the insect, it is thrown into a state similar to that of a person
who has inhaled chloroform; and after what has, in all probability,
proved a pleasant dream, the insect awakes to find itself changed and
beautified.

1293. _Why are the pupæ of grasshoppers and other insects, when about
to undergo transformation, still active and sensitive?_

Because, as there is but a _slight difference_ between the form which
they have in the pupa state, and that which they ultimately assume,
they do not require the state of torpidity to save them from pain, nor
to arrest their movements while their organs are being changed. With
them _the outer skin is thrown off_, and they are then perfect insects.

1294. _Why do caterpillars, when about to pass through the chrysalis
state, attach themselves to the leaves of plants, &c.?_

Because they know instinctively that for a time they will be _unable
to controul their own movements, and to avoid danger_. They therefore
choose secure and dry places, underneath leaves, or in the crevices of
old and dry walls, and there they firmly attach themselves, to await
the time of their liberation.

1295. _Why do insects attach their eggs, to leaves &c.?_

Because, as the eggs have to be preserved during the winter, the insect
attaches them to some surface which will be a _protection to them_.
Generally speaking, the eggs are attached to the permanent stems of
plants, and not to those leafy portions which are liable to fall and
decay. The spider _weaves a silken bag_ in which it deposits its eggs,
and then it hangs the bag in a sheltered situation. Nature keeps her
butterflies, moths, and caterpillars, locked up during the winter, in
their egg-state; and we have to admire the various devices to which,
if we may so speak, the same nature has resorted for the _security_ of
the egg. Many insects enclose their eggs in a silken web; others cover
them with a coat of hair, torn from their own bodies; some glue them
together; and others, like the moth of the silk-worm, glue them to the
leaves upon which they are deposited, that they may not be shaken off
by the wind, or washed away by rain; some again make incisions into
leaves, and hide an egg in each incision; whilst some envelope their
eggs with a soft substance, which forms the first aliment of the young
animal; and some again make a hole in the earth, and, having stored it
with a quantity of proper food, deposit their eggs in it.

[Verse: "Lay up for yourselves treasures in heaven, where neither
moth nor rust doth corrupt, and where thieves do not break through and
steal."--MATT. VI.]

1296. _Why do butterflies fly by day?_

Because they are _organised to enjoy light and warmth_, and they live
upon the sweets of flowers which by day are most accessible.

1297. _Why do moths fly by night?_

Because they are _organised to enjoy subdued light_ and cool air; and
as they take very little food during the short life they have in the
winged state, they find sufficient by night. Some of the moths, like
that of the silk-worm, take no food from the time they escape from the
chrysalis until they die.

Because, also, they form the food of bats, owls, and other of the
night-flying tribes.

1298. _Why are the bodies of moths generally covered with a very thick
down?_

Because, as they fly by night, they are liable to the effects of cold
and damp. The moths, therefore, are nearly all of them covered with
a very thick down, quite distinguishable from the lighter down of
butterflies.

1299. _Why do moths fly against the candle flame?_

Because their eyes are organised _to bear only a small amount of
light_. When, therefore, they come within the light of a candle, their
sight is overpowered and their vision confused; and as they cannot
distinguish objects, they pursue the light itself, and fly against the
flame.

[Verse: "Let him that glorieth glory in this that he understandeth
and knoweth me, that I am the Lord which exercise loving-kindness,
judgment, and righteousness in the earth: for in these things I
delight, saith the Lord."--JER. IX.]

1300. _Why do insects multiply so numerously?_

Because they form the food of larger animals, and especially of birds.
A single pair of sparrows and a nest of young ones have been estimated
to consume upwards of _three thousand_ insects in a week.

1301. _Why does the "death-watch" make a ticking noise?_

Because the insect is one of the beetle tribe, having a horny case upon
its head, _with which it taps upon any hard substance_, the ticking is
the call of the insect to its species, just as the noise made by the
cricket is a note of communication with other crickets.

     There is a superstition connected with the death-watch,
     which, like most superstitions, is based upon the theory of
     _probabilities_. The death-watch is usually heard in the spring
     of the year, and a superstition runs to the effect that some one
     in the house will die before the year has ended. Persons who are
     superstitious are never very strict in the interpretation of
     their predictions; and therefore, whether a person dies in the
     house or out of it, in the same room where the death-watch was
     heard, or across the wide Atlantic, so that there be some kind
     of relationship, or even acquaintance, between the person who
     hears the omen, and the person dying, the event is sure to be
     connected with the prophetic sounds of the death-watch. Little
     weens the small timber-boring beetle, when he is tapping gently
     to call his mate, and perhaps peeping into every corner and
     crevice to find her, that he is sending dismay into the heart of
     some superstitious listener, who, in ignorance of a simple fact,
     overwhelms herself with an imaginary grief.

1302. _Why are insects in the first stage, after leaving the egg, said
to be in the "larva" state?_

Because the term larva is derived from the Latin _larvated_, meaning
masked, clothed as with a mask; the term is meant to express that the
future insect is disguised in its first form.

1303. _Why are insects in the second state said to be in the "pupa"
state?_

Because the term is derived from the Latin _pupa_, from a slight
resemblance in the manner in which the insects are enclosed, to that in
which it was the fashion of the ancients to _bandage their infants_.

1304. _Why are insects in the "pupa" stage also called "chrysalides?"_

Because, as the Latin term implies, it is adorned with gems. Many
chrysalides are _studded with golden and pearl-like spots_.

[Verse: "Thou hast set all the borders of the earth: thou hast made
summer and winter."--PSALM LXXIV.]

1305. _Why are the perfect insects said to be in the "nymph" state?_

Because their joyful existence, and their beautiful forms, give them
a fancied resemblance to the _nymphs of the heathen mythology_. The
nymphs were supposed goddesses of the mountains, forests, meadows, and
waters.

     This term has generally, but very improperly, been also applied to
     the pupa state, so that _pupa_, _chrysalis_, and _nymph_ have all
     been employed to represent one state. This is obviously an error,
     as there is nothing in the condition of the _pupa_ or _chrysalis_
     that can at all accord with the mythological idea of a _nymph_,
     and which, in reference to the beautiful and joyous fly, finds a
     much truer application.




CHAPTER LXVII.


1306. _Whence does the snail obtain its shell?_

Young snails come from the egg _with a shell upon their backs_.

1307. _How does the shell grow with the increase of size of the animal?_

The soft slime which is yielded by the body of the animal, _hardens
upon the orifice of the shell_, and thus increases its size.

[Illustration: Fig. 80.--COMMON GARDEN SNAIL.]

1308. _Why is the shell spiral?_

Partly because of its original formation; but also because, _as the
shell grows_, the opening is elongated; and thrown up, causing the
spiral body of the shell to turn, and so to wind its growth around the
centre.

[Verse: "Notwithstanding they hearkened not unto Moses; but some of
them left it until the morning, and it bred worms, and stank: and Moses
was wrath with them."--EXODUS XVI.]

1309. _Why has the snail four tentacula attached to its head?_

Because the insect, having no other limbs, is provided with those
projecting members, the lower two serving as _feelers_ and the upper
two also as _feelers_ and _eyes_. These, projecting in the front of
the animal, impart to it a consciousness of surrounding objects, and
especially of those which lie in its path.

1310. _Why is the snail able to move, without feet?_

Because it has attached to its body a fringe of muscular skin, which is
capable of considerable contraction and expansion, and by alternately
stretching and shortening this, the snail is able to draw himself along.

1311. _Why do we see no snails in the winter time?_

Because they bury themselves in the ground, or in holes, where they
remain _in a torpid state_ for several months. Before they enter into
the torpid state, they form with their slimy secretion, and with some
earthy matters which they collect, a strong cement with which they seal
up the opening to their shells.

1312. _Why can snails live in shells thus sealed?_

Because they leave, in the thin wall by which they close themselves in,
_a small hole_, too small to admit water, but large enough to let in
sufficient air to carry on their feeble respiration during their winter
sleep.

1313. _Why do insects abound in putrid waters, and in decaying
substances?_

Because they have been endowed with appetites and with constitutions
that enable them to live upon and to enjoy corrupt matter. In this
point of view the maggots of flies are exceedingly useful; a dead
carcass is speedily threaded by them in every direction; thus that
corrupt matter which, in a large mass, would poison the air, is
taken up in small portions by millions of living bodies, and by them
_dispersed_, and becomes innoxious.

[Verse: "For he maketh small the drops of water: they pour down rain
according to the vapour thereof."--JOB XXXV.]

1314. _Why do we see, in tanks of rain water, insects rising to the
surface?_

Because numerous insects pass through their first stages of existence
in _water_, and among them the common gnat. The gnats of the previous
season having deposited their eggs on the sides of the water-butt, the
warm water developes them, and the larvæ of the gnats appear (Fig. 81;
_c_ natural size of larva; _b_ larva magnified).

[Illustration: Fig. 81.--LARVA AND PUPA OF GNAT.

(_Greatly magnified._)]

1315. _Why do they continually rise to the surface of the water?_

Because they require to breathe air, and therefore they come up to
the surface, where, elevating the tube (_b_) above the surface of the
water, they are enabled to breathe.

1316. _Why do some appear to have larger heads than others?_

Those that have apparently larger heads, and that breathe through tubes
attached to their heads (_d_) are in the _pupa_, or second stage of
development, and underneath the large shield by which their heads are
marked, their wings, feet, &c., are being formed.

[Verse: "Because thy loving kindness is better than life, my lips
shall praise thee."--PSALM LXIII.]

1317. _Why, when the water is disturbed, do the larvæ descend more
rapidly than the pupæ?_

Because the pupæ are in a torpid condition, awaiting the formation of
their perfect organs.

1318. _Why are the flies able to escape from the water?_

Because, as their formation becomes perfected, and the fluids of the
body of the pupa become absorbed in the production of the light texture
of the wings, &c., _the body and its case become lighter than the
water_, and rise and float upon the surface. The pupa-case then forms
a natural boat, from which the fly emerges, and spreading its wings,
enters upon the final state of its existence.

[Illustration: Fig. 82.--THE PERFECT GNAT. ESCAPING FROM THE PUPA-CASE.

_(Greatly magnified.)_]

     This interesting metamorphosis may be seen going on in the summer
     time, in every pond, brook, and reservoir. A fine sunny morning
     calls up millions of these little boats from beneath the surface,
     and the diver within that wonderful little bell breaks its sealed
     doors, and flies away to enjoy the bright sunshine.

1319. _Why are beetles denominated "coleoptera?"_

Because they have wings protected by horny sheaths; the term
_coleoptera_ signifies _wings in a sheath_.

[Verse: "They shall lie down in the dust; and the worms shall cover
them."--JOB XXI.]

1320. _Why have beetles hard horny wing-cases?_

Because they live underground, or in holes excavated in wood, &c. If,
therefore, their wings were not protected by a hard and firm covering,
they would be constantly _liable to destruction_ from the movement of
the insect within hard and rough bodies.

[Illustration: Fig. 83.--STAG-BEETLE, SHOWING ITS WINGS UNFOLDED, AND
THE WING-CASES OPEN.]

     The _elytra_, or scaly wings of the genus of scarabæus, or beetle,
     furnish an example of this kind. The true wing of the animal is
     a light, transparent membrane, finer than the finest gauze, and
     not unlike it. It is also, when expanded, in proportion to the
     size of the animal, very large. In order to protect this delicate
     structure, and, perhaps, also to preserve it in a due state of
     suppleness and humidity, a strong, hard case is given to it,
     in the shape of the horny wing which we call the elytron. When
     the animal is at rest, the gauze wings lie folded up under this
     impenetrable shield. When the beetle prepares for flying, he
     raises the integument, and spreads out his thin membrane to the
     air. And it cannot be observed without admiration, what a tissue
     of cordage, _i. e._ of muscular tendons, must run in various and
     complicated, but determinate directions, along this fine surface,
     in order to enable the animal, either to gather it up into a
     certain precise form, whenever it desires to place its wings under
     the shelter which nature hath given to them, or to expand again
     their folds when wanted for action.

[Verse: "The Lord is good; his mercy is everlasting; and his truth
endureth to all generations."--PSALM C.]

     In some insects, the elytra cover the whole body; in others, half;
     in others only a small part of it; but in all, they completely
     hide and cover the true wings. Also,

     Many, or most of the beetle species lodge in holes in the earth,
     environed by hard, rough substances, and have frequently to
     squeeze their way through narrow passages; in which situation,
     wings so tender, and so large, could scarcely have escaped injury,
     without both a firm covering to defend them, and the capacity of
     folding themselves up under its protection.

1321. _Why have many of the beetle tribe large strong horns?_

Because, as they live in holes in the earth, or in excavations in wood,
they use their horns to _dig out their places of retreat_.

1322. _Why has the giraffe a small head?_

Because, being set upon the end of a very long neck, the animal would
be _unable to raise it_ if it were heavy.

1323. _Why has the giraffe a long neck?_

Because it _feeds upon the branches of tall trees_.

1324. _Why has the giraffe a long and flexible tongue?_

Because it is thereby enabled to lay hold of the tender twigs and
branches, _and draw them into its mouth_, avoiding the coarser parts of
the branches.

1325. _Why are the nostrils of the giraffe small and narrow, and
studded with hairs?_

Because the hairs and the peculiar shape of the nasal passages are
designed as a protection against the insects which inhabit the boughs
of the trees upon which the giraffe feeds; and also against the sands
of the desert, which storms raise into almost suffocating clouds.

       *       *       *       *       *

[Illustration: Fig. 84.--GIRAFFE FEEDING.]

[Verse: "Bless the Lord, all his works, in all places of his
dominion: bless the Lord, O my soul."--PSALM CIII.]

1326. The distribution of animals, or _Zoological Geography_, is of
great interest, and should be carefully studied in connection with
_Botanical Geography_ (_see_ 1208). The highest department of the
animal kingdom (writes the Rev. W. Milner) commences with the class of
_Birds_, which may be naturally divided into the three great orders
of ærial, terrestrial, and aquatic. Aggregation into immense flocks
is a distinguishing feature of several species, especially of the
aquatic order, which form separate colonies, building their nests in
the same state, though other spots equally adapted are at no great
distance. Hence the Vogel-bergs, or bird rocks of the northern seas,
one of which at Westmannsharn in the Faroe group of islands, seldom
intruded upon by man, presents a most extraordinary spectacle to the
visitor. The Vogel-berg lies in a frightful chasm in the precipitous
shores of the island, which rise to the height of a thousand feet,
only accessible from the sea by a narrow passage. Here congregate a
host of birds. Thousands of guillemots and auks swim in groups around
the boat which conveys man to their domain, look curiously at him, and
vanish beneath the water to rise in his immediate neighbourhood. The
black guillemot comes close to the very oars. The seal stretches his
head above the waves, not comprehending what has disturbed the repose
of his asylum, while the rapacious skua pursues the puffin and gull.
High in the air the birds seem like bees clustering about the rocks,
whilst lower they fly past so close that they might be knocked down
with a stick. But not less strange is the domicile of this colony.
On some low rocks scarcely projecting above the water sit the glossy
cormorants, turning their long necks on every side. Next are the skua
gulls, regarded with an anxious eye by the kittiwakes above. Nest
follows nest in crowded rows along the whole breadth of the rock, and
nothing is visible but the heads of the mothers and the white rocks
between. A little higher on the narrow shelves sit the guillemots and
auks, arranged as on parade, with their white breasts to the sea, and
so close that a hailstone could not pass between them. The puffins take
the highest station, and, though scarcely visible, betray themselves
by their flying backwards and forwards. The noise of such a multitude
of birds is confounding, and in vain a person asks a question of his
nearest neighbour. The harsh tones of the kittiwakes are heard above
the whole, the intervals being filled with the monotonous note of the
auk, and the softer voice of the guillemot. When Graba, from whose
travels this description is principally drawn, visited the Vogel-berg,
he was tempted by the sight of a crested cormorant to fire a gun, but
what became of it, he remarks, it was impossible to ascertain. The air
was darkened by the birds roused from their repose. Thousands hastened
out of the chasm with a frightful noise, and spread themselves over
the ocean. The puffins came wandering from their holes, and regarded
the universal confusion with comic gestures. The kittiwakes remained
composedly in their nests, whilst the cormorants tumbled headlong into
the sea. Similar great congregations of the feathered race appear where
the shores are rocky high, and precipitous, but this is strikingly the
case, where

    ----"The northern ocean, in vast whirls,
    Boils round the naked melancholy isles
    Of farthest Thule; and the Atlantic surge
    Pours in among the stormy Hebrides.
    Who can recount what transmigrations there
    Are annual made? what nations come and go?
    And how the living clouds on clouds arise?
    Infinite wings! till all the plume-dark air
    And rude resounding shore are one wild cry."

[Verse: "He rained flesh upon them as dust, and feathered fowls like
as the sand of the sea."--PSALM LXXVIII.]

1327. Most terrestrial birds, unacquainted with man, exhibit a
remarkable tameness, and are slow in acquiring a dread of him, even
after repeated lessons that danger is to be apprehended from his
neighbourhood. Mr. Darwin speaks of a gun as almost superfluous in
the unfrequented districts of South America, for with its muzzle he
pushed a hawk off the branch of a tree. Once, while lying down, a
mocking thrush alighted on the edge of a pitcher, made of the shell of
a tortoise, which he was holding in his hand, and began very leisurely
to sip the water, even allowing him to handle it while seated on the
vessel. In Charles Island, which had been colonised about six years, he
saw a boy sitting by a well with a switch in his hand, with which he
killed the doves and finches as they came to drink; and for some time
had been constantly in the habit of waiting by the well for the same
purpose, to provide himself with his dinners. In the Falkland Islands,
at Bourbon, and at Tristan d'Acunha, the same tameness was noticed by
the early visitors. On the other hand, the small birds in the arctic
regions of America, which have never been persecuted, exhibit the
anomalous fact of great wildness. From a review of various facts, Mr.
Darwin concludes, "first, that the wildness of birds with regard to
man is a particular instinct directed against him, and not dependent
on any general degree of caution arising from other sources of danger;
secondly, that it is not acquired by individual birds in a short
time, even when much persecuted; but that in the course of successive
generations it becomes hereditary. Comparatively few young birds in
any one year have been injured by man in England, yet almost all, even
nestlings, are afraid of him; many individuals, however, both at the
Galapagos and at the Falklands, have been pursued and injured by man,
but yet have not learned a salutary dread of him."

[Verse: "As a bird that wandereth from her nest; so is a man that
wandereth from his place."--PSALM XXVII.]

1328. Numerous species of birds may be regarded as the favourites of
nature on account of the gracefulness given to their shape, and the
richly-coloured plumage with which they are adorned, as evidenced in
the gaudy liveries of many of the parrot tribe, and the forms and
hues of the birds of paradise. But they are especially interesting
to man for the faculty of song with which they are endowed; in some,
"most musical, most melancholy," in others, sprightly and animating,
inspiriting the sons of toil under the burdens peculiar to their
station. It deserves to be remarked, as an instance of compensation
and adjustment, that whilst the birds of the temperate zone are far
inferior to those of tropical climes in point of beauty, they have
far more melodious notes in connection with their less attractive
appearance.

1329. From the powerful means of locomotion possessed by several of the
bird tribe, and their great specific levity, air being admitted to the
whole organisation as water to a sponge, it might be inferred, that the
entire atmosphere was intended to be their domain, so that no species
would be limited to a particular region. The common crow flies at the
rate of twenty-five miles an hour; the rapidity of the eider-duck,
_Anas mollissima_, is equal to ninety miles an hour; while the swifts
and hawks travel at the astonishing speed of a hundred and fifty miles
in the same time. It is true that some species have a very extensive
range, as the nightingale, the common wild goose, and several of the
vulture tribe. The same kind of osprey or fishing-eagle that wanders
along the Scottish shores appears upon those of the south of Europe,
and of New Holland. The lammergeyer haunts the heights of the Pyrenees,
the mountains of Abyssinia, and the Mongolian steppes; and the penguin
falcon occurs in Greenland, Europe, America, and Australia. In general,
however, like plants and terrestrial quadrupeds, the birds are subject
to geographical laws, definite limits circumscribing particular groups.
The common grouse of our own country affords a striking exemplification
of this arrangement, as it is nowhere met with out of Great Britain;
and other examples occur of a very scanty area containing a species
not to be found in any other region. The celebrated birds of paradise
we exclusively confined to a small part of the torrid zone, embracing
New Guinea and the contiguous islands; and the beautiful Lories are
inhabitants of the same districts, being quite unknown to the New
World. Parroquets are chiefly occupants of a zone extending a few
degrees beyond each tropic, but the American group is quite distinct
from the African, and neither of these have one in common with the
parrots of India. The great eagle is limited to the highest summits of
the Alps; and the condor, which soars above the peak of the loftiest of
the Andes, never quits that chain. Humming-birds are entirely limited
to the western hemisphere, where a particular species is sometimes
bounded by the range of an island, while others are more extensively
spread, the _Trochilus flammifrons_, common to Lima, being observed by
Captain King upon the coast of the Straits of Magellan, in the depth of
winter, sucking the flowers of a large fuchsia, then in bloom in the
midst of a shower of snow. Among the birds incapable of flight, which
rival the quadrupeds in their size, the intertropical countries of the
globe have their distinct species, presenting similar general features
of organisation, as the ostrich of Africa and Arabia, the cassowary of
Java and Australia, and the touyou of Brazil. In the arctic regions, we
meet with species peculiar to them, the _Strix laeponicus_ or Lapland
owl, and the eider-duck, an inhabitant of the shores, from whose nests
the eider-down is obtained. Several families of maritime birds are
likewise limited to particular oceanic localities. Approaching the
fortieth parallel of latitude, the albatross is seen flitting along
the surface of the waves, and soon afterwards the frigate and other
tropical birds appear, which never wander far beyond the torrid zone.
It thus appears, that, notwithstanding the great locomotive powers of
birds, particular groups have had certain regions assigned to them
as their sphere of existence, which they are adapted to occupy, and
to which they adhere in the main, though it is easy to conceive of
natural causes occasionally constraining to a migration into new and
even distant territories. Captain Smyth informed Mr. Lyell, that when
engaged in his survey of the Mediterranean, he encountered a gale in
the Gulf of Lyons, at the distance of between twenty and thirty leagues
from the coast of France, which bore along many land-birds of various
species, some of which alighted on the ship, while others were thrown
with violence against the sails. In this manner, many an islet in the
deep, after ages of solitude and silence, uninterrupted except by the
wave's wild dash, and the wind's fierce howl, may have received the
song of birds, forced by the tempest from their home, and compelled to
seek a new one under its direction.

[Verse: "There is a path which no fowl knoweth, and which the
vulture's eye hath not seen."--JOB XVIII.]

1330. There is no feature more remarkable in the economy of birds
than the periodical migrations, so systematically conducted, in which
five-sixths of the whole feathered population engage. In the case
of North America, according to an estimate by Dr. Richardson, the
passenger-pigeons form themselves into vast flocks for the journey,
one of which has been calculated to include 2,230,000,000 individuals.
We are familiar with the cuckoo as our visitor in spring, and with
the house-swallow as our guest through the summer, the latter usually
departing in October to the warmer regions of the south, wintering in
Africa, returning again when a more genial season revives its insect
food. By cutting off two claws from the feet of a certain number of
swallows, Dr. Jenner ascertained the fact of the same individuals
re-appearing in their old haunts in the following year, and one was
met with even after the lapse of seven years. The arctic birds migrate
farther south, when the seas, lakes, and rivers become covered with
unbroken sheets of ice; the swans, geese, ducks, divers, and coots
flying off in regular phalanxes to regions where a less rigorous winter
allows of access to the means of life. Hence, soon after, we lose the
swallows, we gain the snipes and other waders, which have fled from
the hard frozen north to our partially frozen morasses, where their
ordinary nutriment may still be obtained. The equinoctial zone, where
the seasonal change is that of humidity and drought furnishes an
example of the same phenomenon. As soon as the Orinoco is swollen by
the rains, overflows its banks, and inundates the country on either
side, an innumerable quantity of aquatics leave its course for the West
India islands on the north, and the valley of the Amazon on the south,
the increased depth of the river, and the flooded state of the shores,
depriving them of the usual supply of fish and insects. Upon the stream
decreasing, and retiring within its bed, the birds return.

[Verse: "The Lord is my light and my salvation; whom shall I fear?
the Lord is the strength of my life; of whom shall I be afraid?"--PSALM
XXVII.]

1331. A comparison between the quadrupeds of the Old and New Worlds
is in every point strikingly in favour of the former. Not only has
the western continent no animals of such giant bulk as those of the
eastern, but no examples of such high organisation, such power and
courage, as the African lion and the Asiatic tiger display. Buffon's
remark must indeed be considerably modified, respecting the cowardice
of the American feline race; for the jaguar of the woods about
the Amazon, when attacked by man, will not hesitate to accept his
challenge, will even become the assailant, nor shrink from an encounter
against the greatest odds. The following passages from the writings of
Humboldt show that this transatlantic animal is not to be despised:--

"The night was gloomy; the Devil's Wall and its denticulated rocks
appeared from time to time at a distance, illuminated by the burning
of the savannahs, or wrapped in ruddy smoke. At the spot where the
bushes were the thickest, our horses were frightened by the yell of an
animal that seemed to follow us closely. It was a large jaguar, that
had roamed for three years among these mountains. He had constantly
escaped the pursuit of the boldest hunters, and had carried off horses
and mules from the midst of enclosures; but, having no want of food,
had _not yet_ attacked men. The negro who conducted us uttered wild
cries. He thought he should frighten the jaguar; but these means were
of course without effect. The jaguar, like the wolf of Europe, follows
travellers even when he will not attack them; the wolf in the open
fields and in unsheltered places, the jaguar skirting the road, and
appearing only at intervals between the bushes."

The same illustrious observer also remarks,--

"Near the Joval, nature assumes an awful and savage aspect. We there
saw the largest jaguar we had ever met with. The natives themselves
were astonished at its prodigious length, which surpassed that of all
the tigers of India I had seen in the collections of Europe."

Still these were extraordinary specimens of the race, and leave the
fact undoubted, that the most formidable of the western _Feræ_ has no
pretensions to an equality with his congener, the tyrant of the jungles
of Bengal.

1332. In vain also we look among the tribes of America for a rival
in outward appearance to the giraffe, so remarkable for its height,
its swan-like neck, gentle habits, and soft expressive eye; while
of the animals most serviceable to mankind--the horse, the ox, the
ass, the goat, and the hog--not a living example of either was known
there before its occupancy by the Europeans. But, however inferior
the animal race of the New may be as compared to those of the Old
world, the balance between the two appears to have been pretty equal
in remote ages; geological discovery has disproved the assertion of
Buffon, that the creative force in America in relation to quadrupeds
never possessed great vigour, and has established the fact, that it is
only the more recent specimens of its energy that are upon an inferior
scale. The relics of the unwieldly magatherium, of the gigantic sloth,
and armadillo-like animals, discovered in great abundance imbedded in
its soil, prove that at a former period it swarmed with monsters of
equal bulk with those that now roam in the midst of Africa and Asia.
The estuary deposit that forms the plains westward of Buenos Ayres,
and covers the gigantic rocks of the Bando Oriental, appears to be the
grave of extinct gigantic quadrupeds.

[Verse: "But wild beasts of the desert shall lie there; and their
houses shall be full of doleful creatures; and owls shall dwell there,
and satyrs shall dance there."--ISAIAH XIV.]

1333. There are various animals which are very widely dispersed,
enduring the extremes of tropical heat and of polar cold, which are
either in a wild condition or in a state of domestication. Wild races,
considered to be varieties of the domestic dog, occur in India,
Sumatra, Australia, Beloochistan, Natolia, Nubia, various parts of
Africa, and both the Americas; while in subjection to man, the dog
is his faithful companion, and has followed his steps into every
diversity of climate and of situation to which he has wandered. The
north temperate zone of the Old Continent appears to be the native
region of the ox, which passes in Lapland within the arctic circle, and
has been spread over South America since its first introduction by the
Spaniards. The horse, originally an inhabitant of the temperate parts
of the Old World, has shared in a similar dispersion, and now exists
in the high latitude of Iceland, in the desolate regions of Patagonia,
and roams wild in immense herds over the Llanos of the Orinoco, leading
a painful and restless life in the burning climate of the tropics.
Humboldt draws a striking picture of the sufferings of these gifts of
the Old World to the New, returned to a savage state in their western
location.

"In the rainy season, the horses that wander in the savannah, and have
not time to reach the rising grounds of the Llanos, perish by hundreds
amidst the overflowings of the rivers. The mares are seen, followed
by their colts, swimming, during a part of the day, to feed upon
grass, the tops of which alone wave above the waters. In this state
they are pursued by the crocodiles; and it is by no means uncommon to
find the prints of the teeth of these carnivorous reptiles on their
thighs. Pressed alternately by excess of drought and of humidity, they
sometimes seek a pool, in the midst of a bare and dusty soil, to quench
their thirst; and at other times flee from water and the overflowing
rivers, as menaced by an enemy that encounters them in every direction.
Harassed during the day by gad-flies and mosquitoes, the horses,
mules, and cows find themselves attacked at night by enormous bats,
that fasten on their backs, and cause wounds which become dangerous,
because they are filled with acaridæ and other hurtful insects. In
the time of great drought, the mules gnaw even the thorny melocactus
(melon-thistle), in order to drink its cooling juice, and draw it
forth as from a vegetable fountain. During the great inundations,
these same animals lead an amphibious life, surrounded by crocodiles
water-serpents, and manatees. Yet, such are the immutable laws of
nature, their races are preserved in the struggle with the elements,
and amid so many sufferings and dangers. When the waters retire, and
the rivers return into their beds, the Savannah is spread over with a
fine odoriferous grass; and the animals of old Europe and Upper Asia
seem to enjoy, as in their native climates the renewed vegetation of
spring."

1334. The first colonists of La Plata landed with seventy-two horses,
in the year 1535, when, owing to a temporary desertion of the colony,
the animals ran wild; and in 1580, only forty-five years afterwards,
it had reached the Straits of Magellan. The ass has a more restricted
range than the horse, not being capable of enduring so great a degree
of cold, though usually far from being considered a delicate animal.
To the warmer parts of the temperate zone, between the 20th and the
40th parallels of latitude, the ass seems best adapted, not propagating
much beyond the 60th, and only occurring in a state of degeneration
beyond the 52nd. The sheep and goat tribe are widely spread, equally
supporting the extremes of temperature. According to Zimmerman, the
_Argali_ or _Mouflon_, the original race of sheep, still exists on all
the great mountains of the two continents; and the _Capricorn_ and
_Ibex_, the ancestors of the common goat inhabit the high European
elevations. From the 64th degree of north latitude the hog is met with
all over the old continent, and also in the islands of the Indian
Ocean, peopled by the Malay race; and since its introduction into the
New World, it has diffused itself over it, from the 50th parallel north
as far as Patagonia. Originally the cat was not known in America,
nor in any part of Oceanica; but it has now spread into almost every
country of the globe. Among animals entirely wild, the most extensively
diffused, are the fox, hare, squirrel, and ermine; but the species
are different in every region of the world; nor is there perhaps one
example to be found of a species perfectly identical naturally existing
in distant localities of the earth.

[Verse: "His going forth is from the end of the heaven, and his
circuit unto the ends of it; and there is nothing hid from the heat
thereof."--PSALM XIX.]

Respecting the _internal constitution and heat of the earth_,
differences of opinion, and some very wild speculation have existed. We
find in Humboldt's "Cosmos" the following remarks:--

1335. "It has been computed at what depths liquid and even gaseous
substances, from the pressure of their own superimposed strata, would
attain a density exceeding that of platinum, or of iridium; and in
order to bring the actual degree of ellipticity, which was known
within very narrow limits, into harmony with the hypothesis of the
infinite compressibility of matter, Leslie conceived the interior of
the Earth to be a hollow sphere, filled with "an imponderable fluid of
enormous expansive force." Such rash and arbitrary conjectures have
given rise, in wholly unscientific circles, to still more fantastic
notions. The hollow sphere has been peopled with plants and animals, on
which two small subterranean revolving planets, Pluto and Proserpine,
were supposed to shed a mild light. A constantly uniform temperature
is supposed to prevail in these inner regions, and the air being
rendered self-luminous by compression, might well render the planets
of this lower world unnecessary. Near the north pole, in 82 deg. of
latitude, an enormous opening is imagined, from which the polar light
visible in Aurora streams forth, and by which a descent into the hollow
sphere may be made. Sir Humphry Davy and myself were repeatedly and
publicly invited by Captain Symmes to undertake this subterranean
expedition; so powerful is the morbid inclination of men to fill unseen
spaces with shapes of wonder, regardless of the counter-evidence of
well-established facts, or universally recognised natural laws. Even
the celebrated Halley, at the end of the 17th century, hollowed out
the earth in his magnetic speculations; a freely rotating subterranean
nucleus was supposed to occasion, by its varying positions, the diurnal
and annual changes of the magnetic declination. It has been attempted
in our own day, in tedious earnest, to invest with a scientific garb
that which, in the pages of the ingenious Holberg, was an amusing
fiction."

The following are among the speculations which Humboldt thus severely
but justly condemns:--

"The increase of temperature observed is about 1 deg. Fahr. for every
fifteen yards of descent. In all probability, however, the increase
will be found to be in a geometrical progression as investigation is
extended; in which case the present crust will be found to be much
thinner than we have calculated it to be. And should this be found
to be correct, the igneous theory will become a subject of much more
importance, in a geological point of view, than we are at present
disposed to consider it. Taking, then, as correct, the present observed
rate of increase, the temperature would be as follows:

    Water will boil at the depth of 2,430 yards.
    Lead melts at the depth of 8,400 yards.
    There is red heat at the depth of 7 miles.
    Gold melts at 21 miles.
    Cast iron at 74 miles.
    Soft iron at 97 miles.

And at the depth of 100 miles there is a temperature equal to the
greatest artificial heat yet observed; a temperature capable of
fusing platina, porcelain, and indeed every refractory substance we
are acquainted with. These temperatures are calculated from Guyton
Morveau's corrected scale of Wedgwood's pyrometer; and if we adopt
them, we find that the earth is fluid at the depth of 100 miles from
the surface, and that even in its present state very little more than
the soil on which we tread is fit for the habitation of organised
beings."

The above is to be found in Mr. Timbs's "Things not Generally Known,"
a little book which professes to set people right upon points on which
they are in error!

[Verse: "He hath filled the hungry with good things; and the rich he
hath sent empty away."--LUKE I.]

Upon this subject Mr. Hunt, in his "Poetry of Science," says:--

1336. "A question of great interest, in a scientific point of view, is
the temperature of the centre of the earth. We are, of course, without
the means of solving this problem; but we advance a little way onwards
in the inquiry by a careful examination of subterranean temperature
at such depths as the enterprise of man enables us to reach. These
researches show us, that where the mean temperature of the climate is
50 deg., the temperature of the rock at 59 fathoms from the surface is
60 deg.; at 132 fathoms it is 70 deg; at 239 fathoms it is 80 deg.;
being an increase of 10 deg. at 59 fathoms deep, or 1 deg. in 35.4
feet; of 10 deg. more at 73 fathoms deeper, or 1 deg. in 43.8 feet; and
of 10 deg. more at 114 fathoms still deeper, or 1 deg. in 64.2 feet.

Although this would indicate an increase to a certain depth of about
one degree in every fifty feet, yet it would appear that the rate of
increase diminishes with the depth. It appears therefore probable, that
the heat of the earth, so far as man can examine it, is due to the
absorption of the solar rays by the surface. The evidences of intense
igneous action at a great depth cannot be denied, but the doctrine of
a cooling mass, and of the existence of an incandescent mass, at the
earth's centre, remains but one of those guesses which active minds
delight in."

Upon the subject of _hunger_ and _thirst_, by which living creatures
are prompted to feast upon the bounties of nature, Sir Charles Bell
says, in "Appendix to Paley's Natural Theology:"--

1337. "Hunger is defined to be a peculiar sensation experienced in the
stomach from a deficiency of food. Such a definition does not greatly
differ from the notions of those who referred the sense of hunger
to the mechanical action of the surfaces of the stomach upon each
other, or to a threatening of chemical action of the gastric juice on
the stomach itself. But an empty stomach does not cause hunger. On
the contrary, the time when the meal has passed the stomach is the
best suited for exercise, and when there is the greatest alacrity of
spirits. The beast of prey feeds at long intervals; the snake and
other cold-blooded animals take food after intervals of days or weeks.
A horse, on the contrary, is always feeding. His stomach, at most,
contains about four gallons, yet throw before him a truss of tares
or lucerne, and he will eat continually. The emptying of the stomach
cannot, therefore, be the cause of hunger.

"The natural appetite is a sensation related to the general condition
of the system, and not simply referable to the state of the stomach;
neither to its action, nor its emptiness, nor the acidity of its
contents; nor in a starved creature will a full stomach satisfy the
desire of food. Under the same impulse which makes us swallow, the
ruminating animal draws the morsel from its own stomach.

1338. "Hunger is well illustrated by thirst. Suppose we take the
definition of thirst--that it is a sense of dryness and constriction in
the back part of the mouth and fauces; the moistening of these parts
will not allay thirst after much fatigue or during fever. In making a
long speech, if a man's mouth is parched, and the dryness is merely
from speaking, it will be relieved by moistening, but if it comes from
the feverish anxiety and excitement attending a public exhibition, his
thirst will not be so removed. The question, as it regards thirst,
was brought to a demonstration by the following circumstance. A man
having a wound low down in his throat, was tortured with thirst; but no
quantity of fluid passing through his mouth and gullet, and escaping by
the wound, was found in any degree to quench his thirst.

"Thirst, then, like hunger, has relation to the general condition of
the animal system--to the necessity for fluid in the circulation. For
this reason, a man dying from loss of blood suffers under intolerable
thirst. In both thirst and hunger, the supply is obtained through the
gratification of an appetite; and as to these appetites, it will be
acknowledged that the pleasures resulting from them far exceed the
pains. They gently solicit for the wants of the body; they are the
perpetual motive and spring to action."

[Verse: "Let us hear the conclusion of the whole matter; Fear
God, and keep his commandments: for this is the whole duty of
man."--ECCLESIASTES XII.]

       *       *       *       *       *

Our task draws near to a conclusion; and we hope that those who have
followed our teachings will thirst after further knowledge; that they
will henceforward regard the great Book of Nature as the work of an
Almighty Hand, and endeavour to find, for everything that Nature does,
the _Reason Why_.

A high perception of the wisdom of the Divine Being, must necessarily
be the result of an intelligent contemplation of the Divine works. To
the ignorant, the name of God is an unmeaning word; it may inspire
fear, but it does not develope love. To the dark mind of the untaught
man, God is no more than one of those mysterious existences that awe
the superstitious, and deter the wicked. There is no grafting of the
soul of the man upon the eternal love. But knowledge brings man into
communion with that Almighty wisdom which is the fountain of all truth
and happiness. To the enlightened man, God is the sun of all goodness,
around whom the attributes of Power, Wisdom, and Love, radiate and fill
the universe. As man's physical eye cannot withstand the light of the
sun, neither can man's spiritual eye see the whole glory of God. But
as we can rejoice in the sunshine, and interpret the mission of the
sunbeam, so can we find happiness in the Divine presence, and gather
wisdom by the contemplation of the Creator's works.

Nature is a great teacher. What a lesson may be gathered from the
germination of a seed; how uniformly the germs obey their destiny.
However carelessly a seed may be set in the ground, the germ which
forms the root, and that which is the architect of the stem, will
seek their way--the one to light, the other to darkness--to fulfil
their duty. The obstruction of granite rocks, cannot force the
rootlet upward, nor drive the leaflet down. They may kill the germs
by exhausting their vital powers in an endeavour to find the proper
elements; but no obstruction can make a single blade of grass do aught
but strive to fulfil the end for which it was created. Would that man
were equally true to the purpose of his existence, and suffered neither
the rocks of selfishness, nor the false light of temptation, to force
or allure him from duty to his God.

THE END.




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but the whole are _fresh and new_, and _suited to the present times_.
As a book to keep in the family for reference, it is unequaled,
_comprising as it does all kinds of Books of Information in a single
volume_.

Send cash orders to

DICK & FITZGERALD. No. 18 Ann Street, New York.

       *       *       *       *       *

LIVE AND LEARN;

A GUIDE FOR ALL WHO WISH TO SPEAK AND WRITE CORRECTLY:

particularly intended as a Book of Reference for the Solution of
Difficulties connected with Grammar, Composition, Punctuation, &c.,
with Explanations of Latin and French words and Phrases of frequent
occurrence in Newspapers, Reviews, Periodicals, and Books in general
containing Examples of

ONE THOUSAND MISTAKES

of Daily Occurrence, in Speaking, Writing and Pronunciation. Together
with Detailed Instructions for Writing for the Press, and forms of
Articles in the various departments of Newspaper Literature. 216 pages,
bound in Cloth, 12mo, price 50 cents, and sent to any address _free of
postage_.

"Live and Learn" is a most useful book, designed as a Guide to Grammar,
Composition, and Punctuation. So few people speak or write really good
grammar, and fewer still punctuate decently, that a book that informs
them how to do so--and not only that indicates their faults, but shows
them how they are to be corrected--cannot fail to be popular; _there is
not a person indeed, who might not learn something from it_.

No work heretofore written on this subject contains one half the really
useful information that the present does. It should be in the hand of
every man, woman and child in the country, and is alike invaluable to
the Scholar, the Merchant, the Farmer, and the Artizan.

There are hundreds of persons engaged in professional and commercial
pursuits, who are sensible of their deficiencies on many points
connected with the grammar of their own tongue, and who, by
self-tuition, are anxious to correct such deficiencies, and to acquire
the means of speaking and writing, if not with elegance at least with
a due regard to grammatical accuracy, to whom this little work is
"indispensible." As a book of reference, "Live and Learn" will settle
many disputes. It ought to be on every table, and be particularly
recommended to the young, before habit makes common blunders uncommon
hard to cure.


OPINIONS OF THE PRESS.

"Live and Learn" is an excellent book. To show our appreciation of
its merits we have had it cased in leather, and have made a pocket
companion of it. We look upon it as really _indispensible_. We advise
our readers to imitate our example--procure the book and sell it not
for any price--_Educational Gazette_.

Such a book as this has long been wanted by those who entertain the
wish alluded to in the title. It is suitable for all classes. We have
attentively conned its pages, and can _recommend it as one of the best
works of reference for the young student, or even the ripe scholar, and
as deserving to be generally consulted. The work is altogether useful
and indispensible.--New York Tribune_.

This book, particularly intended as _a_ work of reference for the
solution of difficulties connected with grammar, composition and
punctuation, etc., etc., will be found useful by those who have not
received a sound elementary education and who nevertheless move in
position.--_Daily Times_.

This capital work not only gives examples of over 1000 mistakes, but
it gives rules for their correction so clear, so terse, and at once
so simple that the most ordinary mind cannot fail to comprehend their
meaning. This is one of the chief beauties of "Live and Learn," for
what is the use of pointing out a grammatical error without giving a
key to its correction? There has been several catchpenny works on this
subject lately issued. They tell the reader that mistakes exist, but
give no rule for their avoidance. If you want a really good work, buy
"Live and Learn."

Send cash orders to

DICK & FITZGERALD, No. 18 Ann St. N. Y.

       *       *       *       *       *

EVERY MAN A MAGICIAN.

THE MAGICIAN'S OWN BOOK; OR, The Whole Art of Conjuring.

Being a Complete Hand-Book of Parlor Magic, containing over One
Thousand Optical, Chemical, Mechanical, Magnetical, and Magical
Experiments, Amusing Transmutations, Astonishing Sleights and
Subtleties, Celebrated Card Deceptions, Ingenious Tricks with Numbers,
Curious and Entertaining Puzzles--Together with all the most Noted
Tricks of Modern Performers. The whole Illustrated with

OVER 500 WOOD CUTS,

And intended as a source of amusement for ONE THOUSAND AND ONE
EVENINGS.

12mo., cloth, 400 pages; gilt side and back stamp. Price, ONE DOLLAR,
sent free of postage.

Here is a book for the long winter evenings, and one that will make
all merry and happy. It contains over a THOUSAND TRICKS, of every
description, and they are all explained so clear and explicitly that
any person can comprehend and perform them with ease. It also contains
numerous CURIOUS PUZZLES, with patterns showing how they are done,
any one of which will afford amusement enough for a whole evening.
There is, also, the best collection of wonderful CARD DECEPTIONS ever
yet published, any one of which is worth more than double the price
of the book. This work also contains a splendid collection of CURIOUS
TRICKS WITH NUMBERS, and embraces several hundred tricks never before
in print. It is no catchpenny affair, but a standard work, containing
every variety of Experiment in Conjuring, Cards, Legerdemain,
Transmutations, the Magic of Chemistry, the Magic of Mechanics, the
Magic of Pneumatics, the Magic of Numbers, the Magic of Art, the Magic
of Strength, the Magic of Magnetism, the Magic of Secret Writing,
Miscellaneous Curious Tricks and Fancies, &c. This book is beautifully
bound in fine cloth, with gilt side and back stamp, and is illustrated
with

OVER 500 WOOD ENGRAVINGS,

Besides a Tinted Title Page and Frontispiece. Price, ONE DOLLAR, and
sent to any address, free of postage.

Send cash orders to

DICK & FITZGERALD, No. 18 Ann Street, New York.

       *       *       *       *       *

THE FOUNTAIN OF ALL KNOWLEDGE.

THE REASON WHY:

A CAREFUL COLLECTION OF Some Thousands of Reasons for Things which,
though Generally Known, are Imperfectly Understood.

A BOOK OF CONDENSED SCIENTIFIC KNOWLEDGE FOR THE MILLION.

BY THE AUTHOR OF "INQUIRE WITHIN."

This is a goodly sized volume of 356 pages, comprising a sort of
Encyclopedia of Scientific Information of all kinds. It is arranged
with an Alphabetical Index, in referring to which you can solve almost
any problem in Natural Philosophy or Learned Science that may come up.
It is a book that will give you the cream of the information that a
long course of practical experiments and profound study has imparted to
the _savants_ and philosophers of this progressive age. It contains a
collection and solution of

Thirteen Hundred & Thirty-Two Facts in Science & Philosophy,

some of which, on their first discovery, puzzled the most learned and
apt scholars.

It is useless to go into details of this excellent work. Suffice it to
say, that it treats on every imaginable subject pertaining to Causes
and Effects, and must necessarily be invaluable to all persons who
desire KNOWLEDGE, and whose means and position in life have prevented
them from acquiring it by a regular and tedious course of Study.

We hesitate not to say, that any one who closely reads this volume
will obtain as much real learning in a few days as years of study and
patient research would afford them in a regular course. In a word it
makes you a learned and refined person with spending but very little
money, time or trouble.

No pains have been spared by the Author to make this a popular book, in
fact a book for the million, and some idea may be formed of its vast
usefulness when we inform the reader that THE REASON WHY has an


Index of Contents requiring Forty Columns of Fine Type.

No person who desires to figure in refined and intelligent circles
should delay purchasing a copy of this capital work, for it will
furnish thousands of ideas and important topics of conversation, so
that the most ignorant person by reading it will be posted up on all
scientific subjects.

What Haydn's Dictionary of Dates is in regard to historical events,
this wonderful book is in respect to scientific facts. The plan of the
book and its execution, leave nothing to be desired. We can cordially
recommend this work to all those inquirers, young and old, of both
sexes, who are never satisfied until they know the "reason why."

The man who goes out into the world, or attempts to attend properly to
his domestic duties, will find himself, however abundantly supplied
with books or bullion, perpetually embarrassed for the want of small
facts and small change. This volume supplies the


Ready Coin of Conversation.

In the shape of SCIENCE FOR THE MILLION, and makes even the neglected
in early studies feel quite at home upon every topic likely to be
discussed within the ordinary range of the social circle. It imparts

Practical Information on the Subject of Practical Facts.

It may be denominated, _Science made easy, or a world of useful
every-day learning condensed into a volume for your pocket!_

THE REASON WHY

Is a handsome 12mo. volume of 356 pages, printed on fine paper, bound
in cloth, gilt, and embellished with a large number of Wood Cuts,
illustrating the various subjects treated of.

PRICE ONE DOLLAR.

[Pointing hand symbol] Copies mailed to any address in the United
States or Canada, free of postage.

Send your Cash orders to DICK & FITZGERALD, Publishers, NO. 18 ANN
STREET, NEW YORK.

       *       *       *       *       *

SAM SLICK'S NEW WORK.

"Buy it, and if you don't laugh, then there is no laugh in you."--OHIO
STATESMAN.


_JUST PUBLISHED,_

NATURE AND HUMAN NATURE

A Sequel to "Wise Saws; or, Sam Slick in Search of a Wife."

BY JUDGE HALIBURTON,

Author of "Sam Slick, the Clockmaker," "Old Judge," &c., &c.

NEATLY BOUND IN MUSLIN, 75 CENTS; IN PAPER, 50 CENTS.


CONTENTS.

    A Surprise.
    Clippers and Steamers.
    Unlocking a Woman's Heart.
    A Critter with a Thousand Virtues and but One Vice.
    A New Way to Learn Gaelic.
    The Wounds of the Heart.
    Fiddling and Dancing, and Serving the Devil.
    Stitching a Button-Hole.
    The Plural of Moore.
    A Day on the Lakes.
    The Betrothal.
    A Foggy Night.
    Female Colleges.
    Gipseying.
    The World before the Flood.
    Lost at Sea.
    Holding up the Mirror.
    The Bundle of Sticks.
    Town and Country.
    The Honeymoon.
    A Dish of Clams.
    The Devil's Hole; or, Fish and Flesh.
    The Cucumber Lake.
    The Recall.


NOTICES OF THE PRESS.

"The writings of Judge Haliburton have long been regarded as the
production of the finest humorist that has ever attempted the
delineation of Yankee character, and the entertaining work before us
shows that he has lost none of his original wit and humor. It will be
difficult to find a volume so full of fun and good sense as this, which
chronicles the last experiences of Sam Slick."--_Commercial Advertiser._

"Since Sam Slick's first work he has written nothing so fresh, racy,
and genuinely humorous as this. Every line of it tells, some way or
other--instructively, satirically, jocosely or wittily."--_London
Observer._

"We sincerely pity the man who cannot find in it the materials for the
loosening of several of his coffin nails. It is full of oddity and fun,
and must sell like new tomatoes."--_Buffalo Express._

Published by DICK & FITZGERALD, 18 Ann St., N. Y.

And for sale by all the principal Booksellers.

[Pointing hand symbol] _Persons forwarding the price by mail will
receive the Work_ FREE OF POSTAGE.[Pointing hand symbol]

       *       *       *       *       *

DICK & CO.'S LIST OF PUBLICATIONS.

A Book for Housekeepers.

       *       *       *       *       *

THE AMERICAN HOME COOK-BOOK.

Containing several hundred

EXCELLENT RECIPES.

The whole based on many years' experience of an American Housewife.
Illustrated with engravings. Price 25 cents.

All the Recipes in this book are written from actual experiments in
Cooking. There are no copying from theoretical cooking recipes. They
are intended for American families, and may be depended upon as good
and practicable. The authoress is a lady who understands how cooking
ought to be done, and has here given her experience. It is a book of
128 pages, and is CHEAP at 25 cents. We expect to sell a very large
number at this low price.

       *       *       *       *       *

Works for the Ladies.


THE LADIES' GUIDE TO BEAUTY.

A COMPANION FOR THE TOILET.

Paper ... 25 cts.
Cloth ... 37-1/2 "

Containing Practical Advice on Improving the Complexion, the Hair, the
Hands, the Form, the Teeth, the Eyes, the Feet, the Features, so as to
insure the highest degree of perfection of which they are susceptible.
And also upwards of One Hundred Recipes for various Cosmetics, Oils,
Pomades, etc., etc., being the result of a combination of Practical
and Scientific Skill. By Sir James Clark, Private Physician to Queen
Victoria. Revised and edited by an American Physician and Chemist.

Price 25 cents, and we send it free of postage.

       *       *       *       *       *

LADIES' GUIDE TO CROCHET.

BY MRS. ANN S. STEVENS.

Copiously illustrated with original and very choice Designs in Crochet,
etc., printed in colors, separate from the letter-press, on tinted
paper. Also with numerous wood-cuts printed with the letter-press,
explanatory of terms, etc. Oblong, pp. 117, beautifully bound in extra
cloth, gilt. Price 75 cents.

This in by far the best work on the subject of Crochet yet published.
There are plenty of other books containing Crochet patterns, but the
difficulty is, they do not have the necessary instructions how to work
them, and are, therefore, useless. This work, however, supplies this
much felt and glaring deficiency, and has the terms in Crochet so
clearly explained that any Crochet pattern, however difficult, may be
worked with ease.

Copies of the above mailed to any address in the United States free of
postage.

       *       *       *       *       *

Books by Celebrated Authors.


WHICH--THE RIGHT OR THE LEFT?

A Religions Novel. Royal 12mo., cloth. 534 pages. Price $1 25.

This work has received favorable notice from the entire secular as
well as the religious press. The main design of the author in the
illustration of the fact that success in business may easily consort
with fervid piety and the strictest honesty on the part of those
engaged in it. The story is that of a young man, the son of a country
pastor, who goes as an assistant into a dry goods store, at New York;
and not only maintains his religious principles amidst the allurements
of the capital, but succeeds in drawing within their happy influence
a number of the clerks and other assistants, who at first scoffed at
his "rural piety," as they termed it, but were at length led by him
to abandon the frivolities which had formed their former delight, and
devote themselves to religious exercises and the visitation of the sick
and poor. His influence reached even a higher circle; and the author
gives us some lively sketches of the insipidity and heartlessness of
fashionable life, whose unhappy devotees choose to live for society and
self, rather than for Religion and their fellow-creatures.

[Inverted asterism symbol] The Publishers have in their possession,
testimonials from over _three hundred_ of the principal Clergymen in
the United States and Canada, pronouncing this to be the best work
that has been published for years, and in every instance they are the
honest convictions formed after an actual perusal of the volume itself.
This work has also received high laudation from almost every paper of
character and standing in this country. Added to which it has been read
by thousands, and has received universal commendation.

       *       *       *       *       *

ESTELLE GRANT; OR, THE LOST WIFE.

Large 12mo., cloth. Price $1 00.

This is a book so thoroughly excellent, so exalted in its character, so
full of exquisite pictures of society, and manifesting so much genius,
skill, and knowledge of human nature, that no one can possibly read
it without admitting it to be, in every way, a noble book. The story,
too, is one of stirring interest; and it either sweeps you along with
its powerful spell, or beguiles you with its tenderness, pathos, and
geniality.

       *       *       *       *       *

THE PILGRIMS OF WALSINGHAM.

A Romance of the Middle Ages, from the accomplished pen of Agnes
Strickland.

Large 12mo., pp. 460. Price $1 00.

Truly a charming book! Full of the profoundest interest, yet not one
improbable incident--not one prurient idea. You will sooner find spots
upon the leaves of the silvery lily than an impure sentence in a book
by this author.--_Buffalo Courier._

       *       *       *       *       *

NA MOTU; OR, REEF ROVINGS IN THE SOUTH SEAS.

A Narrative of Adventures in the Hawaiian, Georgian, and Society
Islands, with original illustrations.

BY EDWARD T. PERKINS

12mo. Cloth. $1 00

Na Motu is the quaint title of a handsome volume of voyage and
adventure in the South Seas. Mr. Perkins, the author, a schoolmate
of Ike Marvel, has spent several years before the mast, and on the
salt water in other capacities, and his style is characterized by a
straightforward, honest nonchalance and idiomatic flavor, redolent of
Old Ocean from stem to stern. His daguerreotype of nautical dialogues
is only a little too perfect, occasionally, for good taste; a large
portion of his experience being gained on a whaling ship.--_New York
Church Jour._

       *       *       *       *       *

_SAM SLICK'S YANKEE COURTSHIP._


RECENTLY PUBLISHED,

WISE SAWS;

OR,

SAM SLICK IN SEARCH OF A WIFE.

By the Author of "Sam Slick In England," "Nature and Human Nature,"
"Sam Slick's Sayings and Doings," &c.

In One Elegant Volume, neatly bound in Muslin;

_Price 75 Cts.--in Paper 50 Cts._


Extract from the Preface:

* * * * "Fun has no limits. It is like the human race and face; there
is a family likeness among all the species, but they all differ. New
combinations produce new varieties. A man who has an eye for fun sees
it in everything. * * * There is a work called 'The Horse,' and another
'The Cow,' and 'The Dog,' and so on; why should'nt there be one on 'The
Galls?' They are about the most difficult to choose and to manage of
any created critter, and yet there aint any dependable directions about
pickin' and choosin' of them. Is it any wonder then so many fellows get
taken in when they go for to swap hearts with them? Besides; any one
can find a gentleman that keeps a livery stable to get him a horse to
order, but who can say, 'This is the Gall for your money!'"


CONTENTS.

    Introductory Letter,
    Chat with the President,
    Stealing a Speech,
    Everything in General, and Nothing in Particular,
    The black Hawk: or Life in a Fore-and-After,
    Old Blowhard,
    The Widow's Son,
    The Language of Mackerel,
    The Best-natured Man in the World,
    The Bait-Box,
    The Water-Glass; or a Day-Dream of Life,
    Old Sarsaparilla Pills,
    Our Colonies and Sailors,
    The House that Hope Built,
    The House without Hope,
    An Old Friend with a New Face,
    Chat in a Calm,
    The Sable Island Ghost,
    The Witch of Eskisoony,
    Jericho beyond Jordan,
    Three Truths for One Lie,
    Aunt Thankful & her Room,
    A Single Idea,
    An Excellent Plan of Reform,
    Goose Van Dam,
    A Hot Day,
    A Pic-Nic at La Haire,
    A Narrow Escape.

Published by DICK & FITZGERALD, 18 Ann St., N. Y.

_And for sale by all the principal Booksellers._

       *       *       *       *       *

THE ARTIST'S BRIDE;

OR, THE PAWNBROKER'S HEIR.

A Novel, by EMERSON BENNET.

12mo. Cloth,--420 pages,--Price 1 00.

"We have perused this work with some attention, and do not hesitate to
pronounce it one of the very best productions of the talented author.
There is not a page that does not glow with thrilling and interesting
incident, and will well repay the reader for the time occupied in
perusing it. The characters are most admirably drawn, and are perfectly
natural throughout. We have derived so much gratification from the
perusal of this charming novel, that we are anxious to make our readers
share it with us: and, at the same time, to recommend it to be read
by all persons who are fond of romantic adventures. Mr. Bennett is a
spirited and vigorous writer, and his works deserve to be generally
read; not only because they are well written, but that they are, in
most part, taken from events connected with the history of our own
country, from which much valuable information is derived, and should,
therefore, have a double claim upon our preference, over those works
where the incidents are gleaned from the romantic legends of old
castles and foreign climes."--_Louisville Journal._

       *       *       *       *       *

DICK TARLETON;

OR,

THE LAST OF HIS RACE.

Containing 112 very large octavo pages. Price 25 cts. and the book
sent free of postage. This well written work has been pronounced by
good judges to be the best of Mr. Smith's production. This is saying a
great deal, considering that gentleman is the author of "Minnie Grey,"
and "Woman and her Master,"--works which have become famous with novel
readers.

       *       *       *       *       *

CYRILLA;

A ROMANCE.

BY THE AUTHOR OF THE INITIALS.

Large Octavo.--Price 50c.

Every person who has read that charming novel, "The Initials," should
purchase a copy of "Cyrilla." It is one of the best novels that has
been published in the past ten years. There is, probably no work of
fiction now before the public that surpasses it for power, pathos,
depth of plot, delineation of character and brilliancy of sentiment. It
forcibly shows that "Many who have perished have erred and sinned for
woman."

Copies of the above books sent by mail free of postage. Send cash
orders to

DICK & FITZGERALD, No. 18 Ann St., New York.

       *       *       *       *       *

New Works by Miss E. Marryatt.

(DAUGHTER OF CAPTAIN MARRYATT.)


HENRY LYLE; OR LIFE AND EXISTENCE.

12mo. Cloth, Price $1 00.

       *       *       *       *       *

TEMPER; A TALE.

12mo. Cloth, Price $1 00.

The above novels, by the talented daughter of the late Captain
Marryatt, were written in compliance with the wishes of her father,
expressed a short time previous to his death; and the fair authoress
alludes to this circumstance by way of apology, in the preface
to "Temper." We predict for them a wide spread popularity. They
are original in style, truly moral and religious in tone, and are
calculated to accomplish much good, as the author aims some telling
blows at the tendency of the present generation towards _Infidelity_,
and other modern evils.

       *       *       *       *       *

Works by the Author of "Zaidee."

ADAM GRAEME OF MOSSGRAY.

12mo. Cloth. Price $1 00.

The characters are painted in bold relief, and seem to live, move
and speak before you. Not one is overdrawn, and yet each comes up to
the popular standard, in point of interest, individualization, and
spirit. The tale is, indeed, "sad, high and working; full of state and
woe;" but it is pleasant enough for all that, and the sober, truthful
earnestness with which it is related, will at once communicate itself
to the mind of the most fastidious and hypercritical peruser of modern
volumes.

       *       *       *       *       *

MAGDALEN HEPBURN;

A Story of the Scottish Reformation.

12mo. Cloth, Price $1 00.

This charming novel, by the author of "Zaidee," will be welcomed by
all who have had the pleasure of reading the former production. The
quaint originality, the healthy and cheerful religious tone, and
charming simplicity and good sense of this volume, will render it a
general and permanent favorite. A work which will be read as long as
any volume of our time. We know of no fiction, in fact, that we would
sooner recommend; for, while it will fascinate all who merely read
for amusement, it will delight as well as improve those who seek for
something even in a novel. It is fascinating from beginning to ending,
and no reader will lay it down, after perusal, without wishing the
author had extended its pages.

       *       *       *       *       *

A REPLY TO "DRED," AND "UNCLE TOM."

TIT FOR TAT;

A NOVEL,

BY A LADY OF NEW ORLEANS.

12mo. Cloth, Price $1. Sent free of postage.

This the title of a most wonderful book, written by a lady of New
Orleans, and issued from the press for the perusal of all persons whose
minds have been poisoned by the pernicious exaggerations of American
life and Negro Slavery to be found in "Uncle Tom's Cabin" and "Dred."
The lady of New Orleans has done her work manfully. The book shows
clearly that those who cry out against Negro Slavery, and utter the
rankest falsehoods about that institution, are the supporters and
proprietors of a system of _white_ slavery more cruel and debasing in
its character and operations than the most skilful romancist could
imagine. All this is shown in a Tale abounding with spirited and
dramatic scenes and incidents. "TIT FOR TAT" embraces forty chapters
of astonishing interest. MILLIONS of copies of this work should be
circulated.


OPINIONS OF THE PRESS.

"It recounts, in a forcible manner, the evils of the English social
system.... We only wish it furnished any sufficient apology for our
shortcomings."--_Commercial, Buffalo._

"One of the must powerfully written novels of the day."--_Springfield
Republican._

"It is a poem in all its parts; fervid, womanly and
eloquent."--_Galveston News._

"She shows clearly that those who cry out against Negro Slavery
are the supporters of a system of white Slavery, most cruel and
depraved."--_Savannah News._

This is "carrying the war into Africa" with a vengeance. It is more
than "a Roland for an Oliver." It is more caustic than even "Change
for Dickens' American Notes. By a lady." "Dred, a Tale of the Dismal
Swamp," the offspring of foreign influence; British influence;
subsidising and Anglicising the Yankee pen of Harriet Beecher Stowe, is
answered most effectually in a tale of white slavery, far more dismal
than all the caricatures that have ever been painted of Negro servitude
in the South. Our bane and antidote are both before us. "Tit for Tat"
is confined to England and the English, and is, therefore, a more
direct and appropriate reply to the Duchess of Sutherland's minion. The
bold, startling pictures are drawn from real life, and their darkest
shadows do not exaggerate the depths of degradation and misery into
which the fairest specimens of God's handiwork are plunged; white men
capable of appreciating misery in its highest forms, and of enjoying
all its benefits and refinements. And all the suffering and woe
depicted by the author with masculine vigor are the direct results of
the cruel oppression of the aristocracy, to whom Mrs. Stowe plays the
flunkey, flattering in their vices, the tyrants who wallow in luxury
upon the toil and blood of the people.--_New York Citizen._

Copies of the above books sent per mail free of postage. Send cash
orders to

DICK & FITZGERALD. No. 18 Ann Street, New York.



  +--------------------------------------------------------------------+
  | TRANSCRIBER'S NOTE:                                                |
  |                                                                    |
  | Minor typographical errors have been corrected without note.       |
  |                                                                    |
  | Punctuation and spelling were made consistent when a predominant   |
  | form was found in this book; otherwise they were not changed.      |
  |                                                                    |
  | Ambiguous hyphens at the ends of lines were retained.              |
  |                                                                    |
  | Mid-paragraph illustrations have been moved between paragraphs and |
  | some illustrations have been moved closer to the text that         |
  | references them. The List of Illustrations paginations were        |
  | changed accordingly.                                               |
  |                                                                    |
  | Italicized words are surrounded by underline characters,           |
  | _like this_.                                                       |
  |                                                                    |
  | Each page starts with a biblical quotation. These were enclosed in |
  | square brackets, labeled verses and moved between paragraphs when  |
  | needed.                                                            |
  |                                                                    |
  | Other Notes:                                                       |
  |                                                                    |
  | p. ix: LESSON XI follows LESSON XII. This was not changed.         |
  |                                                                    |
  | p. 151: Two consecutive questions are labeled 666. This was not    |
  | changed.                                                           |
  |                                                                    |
  | p. 177: Question 892 was mislabeled.  Changed to 802.              |
  |                                                                    |
  | p. 232: "F. The muscle situated underneath, ..." This muscle is    |
  | shown above in Fig. 61.                                            |
  |                                                                    |
  | pp. 199 and 201 each have a question 869.  This was not changed.   |
  |                                                                    |
  | p. 251: "... that required to be removed..." changed to "... that  |
  | are required to be removed"...                                     |
  |                                                                    |
  | p. 253: "... destruction of the optic,..." changed to              |
  | "... destruction of the optic nerve,..."                           |
  |                                                                    |
  | p. 286: "... that minerals, and animals..." changed to             |
  | "... animals..."                                                   |
  |                                                                    |
  | p. 293: Two consecutive questions are labeled 666. This was not    |
  | changed.                                                           |
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