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[Illustration: MARCONI WIRELESS TELEGRAPH STATION, CLIFDEN, IRELAND]

Photographed at night while sending a message across the Atlantic.

The terrific snapping of the electric discharge is heard by one standing
near the station, but no light is seen. The strange light given out from
the network of wires is invisible to the eye, but is caught by the
photographic plate.

[Illustration: THE SAME STATION PHOTOGRAPHED BY DAYLIGHT]




    THE STORY OF GREAT INVENTIONS

    BY ELMER ELLSWORTH BURNS


    INSTRUCTOR IN PHYSICS IN THE
    JOSEPH MEDILL HIGH SCHOOL, CHICAGO

    WITH MANY ILLUSTRATIONS

    HARPER & BROTHERS PUBLISHERS
    NEW YORK AND LONDON
    MCMX


    Copyright, 1910, by HARPER & BROTHERS

    Published November, 1910.
    _Printed in the United States of America_




CONTENTS


    CHAPTER I

    THE AGE OF ARCHIMEDES

    Archimedes the first great inventor.--The battle of
    Syracuse.--Archimedes' principle.--Inventions of the ancient
    Greeks


    CHAPTER II

    THE AGE OF GALILEO

    Galileo and the battle for truth.--The pendulum
    clock.--Galileo's experiment with falling shot.--The
    telescope.--Galileo's struggle.--Torricelli and the
    barometer.--Otto von Guericke and the air-pump.--Robert Boyle
    and the pressure of air and steam.--Pascal and the hydraulic
    press.--Newton.--Gravitation.--Colors in sunlight


    CHAPTER III

    THE EIGHTEENTH CENTURY

    James Watt and the steam-engine.--The first steam-engine with a
    piston.--Newcomen's engine.--Watt's engine.--Horse-power of an
    engine.--The Leyden jar.--Conductors and insulators.--Two kinds
    of electric charge.--Franklin's kite experiment.--The
    lightning-rod.--Galvani and the electric current.--Volta and the
    electric battery


    CHAPTER IV

    FARADAY AND THE FIRST DYNAMO

    Count Rumford.--Count Rumford's experiment with the
    cannon.--Davy.--Faraday's electrical discoveries.--Oersted and
    electromagnetism.--Ampère.--Arago.--Faraday's first electric
    motor.--An electric current produced by a magnet.--Detecting and
    measuring an electric current.--An electric current produced by
    the magnetic field of another current.--Faraday's dynamo.--A
    wonderful law of nature


    CHAPTER V

    GREAT INVENTIONS OF THE NINETEENTH CENTURY

    Electric batteries.--The dry battery.--The storage battery.--The
    dynamo.--Siemens' dynamo.--The drum armature.--Edison's
    compound-wound dynamo.--Electric power.--The first electric
    railway.--Electric lighting.--The telegraph.--Duplex
    telegraphy.--The telephone.--The phonograph.--Gas-engines.--The
    steam locomotive.--How a locomotive works.--The turbine


    CHAPTER VI

    THE TWENTIETH-CENTURY OUTLOOK

    Air-ships.--The aeroplane.--How the Wright aeroplane is kept
    afloat.--Submarines.--Some spinning tops that are useful.--The
    monorail-car.--Liquid air and the greatest cold.--The electric
    furnace and the greatest heat.--The wireless telegraph.--The
    wireless telephone.--Wonders of the alternating current.--X-rays
    and radium


    APPENDIX

    Brief notes on important inventions


    INDEX




    ILLUSTRATIONS


    FIG.

    MARCONI WIRELESS-TELEGRAPH STATION, CLIFDEN, IRELAND
    THE SAME STATION PHOTOGRAPHED BY DAYLIGHT

    1--THE BATTLE OF SYRACUSE

    2--GALILEO'S PENDULUM CLOCK

    3--AN AIR THERMOMETER

    4--TORRICELLI'S EXPERIMENT

    5--GUERICKE'S AIR-PUMP

    6--GUERICKE'S WATER BAROMETER

    7--A LIFT-PUMP

    8--A SIMPLE HYDRAULIC PRESS

    9--HOW AN HYDRAULIC PRESS WORKS

    10--AN HYDRAULIC PRESS WITH BELT-DRIVEN PUMP

    11--NEWTON'S EXPERIMENT WITH THE PRISM

    12--PAPIN'S ENGINE

    13--THE NEWCOMEN ENGINE, IN REPAIRING WHICH WATT WAS LED TO HIS
        GREAT DISCOVERIES

    14--CYLINDER OF WATT'S STEAM-ENGINE

    15--A FLY-BALL GOVERNOR

    16--A LEYDEN JAR

    17--FRANKLIN'S KITE EXPERIMENT

    18--VOLTA EXPLAINING HIS ELECTRIC BATTERY TO NAPOLEON BONAPARTE

    19--THE FIRST ELECTRIC BATTERY

    20--COUNT RUMFORD'S EXPERIMENT WITH THE CANNON, MAKING WATER
        BOIL WITHOUT FIRE

    21--OERSTED'S EXPERIMENT

    22--A COIL WITH A CURRENT FLOWING THROUGH IT ACTS LIKE A MAGNET

    23--A BAR OF SOFT IRON WITH A CURRENT FLOWING AROUND IT BECOMES
    A MAGNET

    24--TWO COILS WITH CURRENTS FLOWING IN THE SAME DIRECTION
        ATTRACT EACH OTHER

    25--TWO COILS WITH CURRENTS FLOWING IN OPPOSITE DIRECTIONS REPEL
        EACH OTHER

    26--ARAGO'S EXPERIMENT

    27--ONE POLE OF A MAGNET SPINS ROUND A WIRE THROUGH WHICH AN
        ELECTRIC CURRENT FLOWS

    28--WHEN A MAGNET IS THRUST INTO A COIL OF WIRE IT CAUSES A
        CURRENT TO FLOW IN THE COIL, BUT THE CURRENT FLOWS ONLY
        WHILE THE MAGNET IS MOVING

    29--A COIL OF WIRE AROUND A COMPASS-NEEDLE

    30--FARADAY'S INDUCTION-COIL

    31--HISTORICAL APPARATUS OF FARADAY IN THE ROYAL INSTITUTION

    32--FARADAY'S FIRST DYNAMO

    33--FARADAY'S LABORATORY, WHERE THE FIRST DYNAMO WAS MADE

    34--THE FIRST TRANSFORMER

    35--THE "MAGNETIC FIELD" IS THE SPACE AROUND A MAGNET IN WHICH
        IT WILL ATTRACT IRON

    36--MAGNETIC FIELD OF A HORSESHOE MAGNET

    37--A DANIELL CELL

    38--A GRAVITY CELL

    39--SHOWING WHAT IS IN A DRY BATTERY

    40--A STORAGE BATTERY, SHOWING THE "GRIDS"

    41--A STORAGE-BATTERY PLATE MADE FROM A SHEET OF LEAD

    42--STURGEON'S ELECTROMAGNET

    43--AN ELECTROMAGNET WITH MANY TURNS OF INSULATED WIRE

    44--AN ELECTROMAGNET LIFTING TWELVE TONS OF IRON

    45--A DYNAMO WITH SIEMENS' ARMATURE

    46--RING ARMATURE

    47--FIRST DYNAMO PATENTED IN THE UNITED STATES

    48--A DRUM ARMATURE, SHOWING HOW AN ARMATURE OF FOUR COILS IS
        WOUND

    49--A SERIES-WOUND DYNAMO

    50--A SHUNT-WOUND DYNAMO

    51--A COMPOUND-WOUND DYNAMO

    52--ONE OF EDISON'S FIRST DYNAMOS

    53--A DYNAMO MOUNTED ON THE TRUCK OF A RAILWAY CAR

    54--FIRST ELECTRIC LOCOMOTIVE

    55--FIRST EDISON ELECTRIC LOCOMOTIVE

    56--EDISON'S FIRST PASSENGER LOCOMOTIVE

    57--FIRST COMMERCIAL ELECTRIC RAILWAY

    58--EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS
        LABORATORY

    59--EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF

    60--FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT; INSTALLED
        ON THE STEAMSHIP "COLUMBIA" IN MAY,

    61--A TELEGRAPH SOUNDER

    62--MORSE'S FIRST TELEGRAPH INSTRUMENT

    63--A TELEGRAPHIC CIRCUIT WITH RELAY AND SOUNDER

    64--A SIMPLE TELEGRAPHIC CIRCUIT

    65--FIRST TELEGRAPH INSTRUMENT USED FOR COMMERCIAL WORK

    66--HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIME

    67--HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE SAME TIME.
        BRIDGE METHOD

    68--FIRST BELL TELEPHONE RECEIVER AND TRANSMITTER

    69--A TELEPHONE RECEIVER

    70--TWO RECEIVERS USED AS A COMPLETE TELEPHONE

    71--CARBON-DUST TRANSMITTER

    72--THE PHONAUTOGRAPH, A FORERUNNER OF THE PHONOGRAPH

    73--EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENT

    74 to--THE FOUR-CYCLE GAS-ENGINE

    78--TWO-CYCLE GAS-ENGINE. CRANK AND CONNECTING-ROD ARE ENCLOSED
        WITH THE PISTON

    79--SELDEN "EXPLOSION BUGGY," FORERUNNER OF THE MODERN
        AUTOMOBILE

    80--SOME EARLY LOCOMOTIVES

    81--HOW A LOCOMOTIVE WORKS

    82--HERO'S ENGINE

    83--AN UNDERSHOT WATER-WHEEL WITH CURVED BLADES

    84--AN OVERSHOT WATER-WHEEL

    85--DE LAVAL STEAM-TURBINE

    86--A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADES

    87--DIAGRAM OF TURBINE SHOWN IN FIG.

    88--A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000
        ELECTRICAL HORSE-POWER

    89--BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR FLIGHT

    90--BASKET, MOTOR, AND PROPELLER OF THE BRITISH ARMY AIR-SHIP
        "NULLI SECUNDUS"

    91--A ZEPPELIN AIR-SHIP

    92--COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST AIR-SHIP IN
        REGULAR PASSENGER SERVICE

    93--THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMY

    94--IN FULL FLIGHT

    95--WRIGHT AIR-SHIP IN FLIGHT

    96--HOW THE WRIGHT AIR-SHIP IS KEPT AFLOAT

    97--THE SEAT AND MOTOR OF THE WRIGHT AEROPLANE

    98--THE BLÉRIOT MONOPLANE

    99--THE "PLUNGER"

    100--U. S. SUBMARINE "SHARK" READY FOR A DIVE

    101--FIRST SUBMARINE CONSTRUCTED IN THE UNITED STATES. IT WENT
         TO THE BOTTOM WITH SEVEN MEN, WHO WERE DROWNED

    102--HOW MEN IN A SUBMARINE SEE WHEN UNDER THE WATER

    103--A TOP THAT SPINS ON A STRING

    104--A CAR THAT RUNS ON ONE RAIL

    105--MANUFACTURING DIAMONDS--FIRST OPERATION

    106--MANUFACTURING DIAMONDS--SECOND OPERATION

    107--MANUFACTURING DIAMONDS--THIRD OPERATION

    108--MARCONI AND HIS WIRELESS-TELEGRAPH SENDING AND RECEIVING
         INSTRUMENTS

    109--DIAGRAM OF WIRELESS-TELEGRAPH SENDING APPARATUS

    110--DIAGRAM OF MARCONI WIRELESS-TELEGRAPH RECEIVING APPARATUS

    111--RECEIVER OF BELL'S PHOTOPHONE

    112--A GAS FLAME IS SENSITIVE TO ELECTRIC WAVES

    113--CAPTAIN INGERSOLL ON BOARD THE U. S. BATTLE-SHIP
         "CONNECTICUT" USING THE WIRELESS TELEPHONE

    114--INCANDESCENT ELECTRIC LAMP LIGHTED THOUGH NOT CONNECTED TO
         ANY BATTERY OR DYNAMO

    115--AN ELECTRIC DISCHARGE AT A PRESSURE OF 12,000,000 VOLTS, A
         CURRENT OF 800 AMPERES IN THE SECONDARY COIL

    116--AN ELECTRIC DISCHARGE SIXTY-FIVE FEET IN LENGTH

    117--A PHYSICIAN EXAMINING THE BONES OF THE ARM BY MEANS OF
         X-RAYS

    118--X-RAY PHOTOGRAPH OF THE EYE

    119--PHOTOGRAPH MADE WITH RADIUM




INTRODUCTORY NOTE


Great inventions are a never-failing source of interest to all of us,
and particularly to the boy in his teens. The dynamo, the electric
motor, the telegraph, with and without wires, the telephone, air-ships,
and many other inventions excite in him an interest which is deeper than
mere curiosity. He wants to know how these things work, and how they
were invented. The man is so absorbed in the present that he cares
little for the past. Not so with the boy. He cares for the history of
inventions, and in this he is wiser than the man, for it is only by a
study of its origin and growth that we can understand the larger
significance of a great invention.

Great inventions have their origin in great discoveries. The story of
great inventions, therefore, includes the story of the discoveries out
of which they have arisen. The stories of the discoveries and the
inventions are inseparable from the lives of the men who made them, and
so we must deal with biography, which in itself is of interest to the
boy. Such a story is the story of physical science in the service of
humanity.

The interest of the youth in great inventions is unquestioned. Shall we
stifle this interest by overemphasis of technical detail, or shall we
minister to it as a thing vital in the life of the youth of to-day?

A few sentences quoted from G. Stanley Hall will indicate the author's
point of view. "The youth is in the humanist stage. Nature is sentiment
before it becomes idea or formula or utility." "The heroes and history
epochs of each branch [of science] add another needed quality to the
still so largely humanistic stage." "A new discovery, besides its
technical record, involves the added duty of concise and lucid popular
statement as a tribute to youth." The need of a "concise and lucid
popular statement" of the rise of the great inventions which form the
material basis of our modern civilization and all of which are new to
the young mind, has no doubt been keenly felt by others as it has been
by the author. The story of our great inventions has been told in sundry
volumes for adult readers, but nowhere has this story, alive with human
interest, been told in a form suited to the young. It was the
realization of this need growing out of years of experience in teaching
these branches that led the author to attempt the task of writing the
story.

The purpose of this book is to tell in simple language how our great
inventions came into being, to depict the life-struggles of the men who
made them, and, in the telling of the story, to explain the working of
the inventions in a way the boy can understand. The stories which are
here woven together present the great epochs in the history of physics,
and are intended to give to the young reader a connected view of the way
in which our great inventions have arisen out of scientific discovery on
the one hand, and conditions which we may call social and economic on
the other hand. If the book shall appeal to young readers, and lead them
to an appreciation of the meaning of a great invention, the author will
feel that his purpose has been achieved.

The author is deeply indebted to Dr. Charles A. McMurry and Prof. Newell
D. Gilbert, of the Northern Illinois State Normal School; Profs. C. R.
Mann and R. A. Millikan, of the University of Chicago; and Prof. John F.
Woodhull, of Columbia University, for reading the manuscript and
offering valuable suggestions. Acknowledgment is further made here of
valuable aid in collecting material for illustrations and letter-press.
Such acknowledgment is due to Prof. A. Gray, University of Glasgow;
Prof. Antonio Favaro, Royal University of Padua; Prof. A. Zammarchi,
Brescia, Italy; Mr. Nikola Tesla; the Royal Institution, London;
_McClure's Magazine_; _The Technical World Magazine_; _The Scientific
American_; the Ellsworth Company; Commonwealth-Edison Company;
Association of Edison Illuminating Companies; Electric Controller and
Supply Company; Kelley-Koett Manufacturing Company; Watson-Stillman
Company; Gould Storage Battery Company; Thordarson Electric Company; the
Westinghouse Machine Company; Marconi Wireless Telegraph Company of
America, and the Siemens-Schuckert Werke, Berlin.

The drawings illustrating Faraday's experiments are from exact
reproductions of Faraday's apparatus, made by Mr. Joseph G. Branch,
author of _Conversations on Electricity_, and are reproduced by his kind
permission.

    E. E. B.

    CHICAGO, _June, 1910_.




THE STORY OF GREAT INVENTIONS




Chapter I

THE AGE OF ARCHIMEDES

    Archimedes, the First Great Inventor


Archimedes, the first great inventor, lived in Syracuse more than two
thousand years ago. Syracuse was a Greek city on the island of Sicily.
The King of Syracuse, Hiero, took great interest in the discoveries of
Archimedes.

One day Archimedes said to King Hiero that with his own strength he
could move any weight whatever. He even said that, if there were another
earth to which he could go, he could move this earth wherever he
pleased. The King, full of wonder, begged of him to prove the truth of
his statement by moving some very heavy weight. Whereupon Archimedes
caused one of the King's galleys to be drawn ashore. This required many
hands and much labor. Having manned the ship and put on board her usual
loading, he placed himself at a distance and easily moved with his hand
the end of a machine which consisted of a variety of ropes and pulleys,
drawing the ship over the sand in as smooth and gentle a manner as if
she had been under sail. The King, quite astonished, prevailed with
Archimedes to make for him all manner of machines which could be used
either for attack or defence in a siege.

    The Battle of Syracuse

During the life of King Hiero Syracuse had no occasion to use the war
machines of Archimedes. The grandson of King Hiero, who succeeded to the
throne, was a tyrant. He attempted to throw off the sovereignty of Rome
and entered into an alliance with Carthage. His cruelty toward his own
people was so great that, after a short reign, he was assassinated.
There was anarchy in Syracuse for a time, the Roman and anti-Roman
parties striving for supremacy. The anti-Roman party gaining possession
of the city, the Romans, in order to bring Syracuse again into
subjection, prepared for an attack by sea and land. Then it was that
Syracuse had need of the war machines made by Archimedes (Fig. 1).

[Illustration: FIG. 1--THE BATTLE OF SYRACUSE
  The city defended by the inventions of Archimedes.]

The Romans came with a large land force and a fleet. They were sure that
within five days they could conquer the city. But there are times when
one man with brains is worth more than an army. In the battle which
followed, Archimedes with his inventions was more than a match for the
Romans.

The city was strong from the fact that the wall on one side lay along a
chain of hills with overhanging brows; on the other side the wall had
its foundation close down by the sea.

A fleet of sixty ships commanded by Marcellus bore down upon the city.
The ships were full of men armed with bows and slings and javelins with
which to dislodge the men who fought on the battlements. Eight ships had
been fastened together in pairs. These double vessels were rowed by the
outer oars of each of the pair. On each pair of ships was a ladder four
feet wide and of a height to reach to the top of the wall. Each side of
the ladder was protected by a railing, and a small roof-like covering,
called a penthouse, was fastened to the upper end of the ladder. This
covering served to protect the soldiers until they could reach the top
of the wall. They thought to bring these double ships close to shore,
raise the ladders by ropes and pulleys until they rested against the
wall, then scale the wall and capture the city.

But Archimedes had crossbows ready, and, when the ships were still at
some distance, he shot stones and darts at the enemy, wounding and
greatly annoying them. When these began to carry over their heads, he
used smaller crossbows of shorter range, so that stones and darts fell
constantly in their midst. By this means he checked their advance, and
finally Marcellus, in despair, was obliged to bring up his ships under
cover of night. But when they had come close to land, and so too near to
be hit by the crossbows, they found that Archimedes had another
contrivance ready. He had pierced the wall as high as a man's head with
many loopholes which on the outside were about as big as the palm of the
hand. Inside the wall he had stationed archers and men with crossbows to
shoot down the marines. By these means he not only baffled the enemy,
but killed the greater number of them. When they tried to use their
ladders, they discovered that he had cranes ready all along the walls,
not visible at other times but which suddenly reared themselves above
the wall from the inside and stretched their beams far over the
battlements, some of them carrying stones weighing about five hundred
pounds, and others great masses of lead. So, whenever the ships came
near, these beams swung round on their pivots and by means of a rope
running through a pulley dropped the stones upon the ships. The result
was that they not only smashed the ships to pieces, but killed many of
the soldiers on board.

Another machine made by Archimedes was an "iron hand" or grappling-hook
swung on a chain and carried by a crane. The hook was dropped on the
prow of a ship, and when it had taken hold the ship was lifted until it
stood on its stern, then quickly dropped, causing it either to sink or
ship a great quantity of water.

With such machines, unknown before, Archimedes drove back the enemy. On
the landward side similar machines were used. The Romans were reduced to
such a state of terror that "if they saw but a rope or a stick put over
the walls they cried out that Archimedes was levelling some machine at
them and turned their backs and fled."

After a long siege, however, hunger forced the Syracusans to surrender.
Marcellus so admired the genius of Archimedes that he gave orders that
he should not be injured. Yet, in the sack of the city which followed,
Archimedes was slain by a Roman soldier.

The Roman historian Livy records that "Archimedes, while intent on some
figures which he had made in the dust, although the confusion was as
great as could possibly be, was put to death by a soldier who did not
know who he was; that Marcellus was greatly grieved at this, and that
pains were taken about his funeral, while his relations also were
carefully sought and received honor and protection on account of his
name and memory."

    Archimedes' Principle

Hiero, when he became King of Syracuse, decreed that a crown of gold, of
great value, should be placed in a certain temple as an offering to the
gods, and sent to a manufacturer the correct weight of gold. In due time
the crown was brought to the King, and a beautiful piece of work it was.
The weight of the crown was the same as that of the gold, but a report
was circulated that some of the gold had been taken out and silver
supplied in its place. Hiero was angry, but knew no method by which the
theft might be detected. He therefore requested Archimedes to give the
matter his attention.

While trying to solve this problem Archimedes went one day to a bath. As
he got into the bath-tub he saw that as his body became immersed the
water ran out of the tub. He quickly saw how he could solve the problem,
leaped out of the bath in joy, and, running home naked, cried out with a
loud voice "Eureka! eureka!" (I have found it! I have found it!)

Using a piece of gold and a piece of silver, each equal in weight to the
crown, and a large vase full of water, he proved that the crown was not
pure gold, and found how much silver had been mixed with the gold.

The incident of the golden crown may have been the starting-point of
Archimedes' study of solid bodies when immersed in fluids. Every one
knows that a boy can lift a heavy stone under water that he could not
lift out of water. The stone seems lighter when in the water. A diver
with his lead-soled shoes could scarcely walk on land, but walks easily
under water. When the diver comes up, the place where he was immediately
becomes filled with water. Now, whatever that water weighs which fills
the diver's place, just that much weight will the diver lose when he
goes down. What is true of the diver is true of the stone or of any
object under water. The stone when in the water loses just as much
weight as the weight of the water that would fill its place. This is the
fact which was discovered by Archimedes and which is called "Archimedes'
Principle."

It is said by an ancient author that Archimedes invented more than forty
machines. Of these the best known are the block and tackle, the endless
screw (worm gear), and the water snail, or Archimedean screw. Yet his
delight was not in his machines, but in his mathematics. Though he had
invented machines to please his king, he regarded such work as trifling,
and took little interest in the common needs of life.

    Inventions of the Ancient Greeks

The common needs of life are to-day the chief concern of the greatest
men, and so we find it hard to sympathize with this view of Archimedes.
His view, however, was that of other learned men of his time, that the
common needs of life are beneath the dignity of the scholar, and so we
can see why the Greeks made so few great inventions.

Hero, who lived a century later than Archimedes, invented a
steam-engine, which, however, was only a toy. A water-clock, in which
the first cog-wheels were used, was invented by another Greek named
Ktesibus, who also invented the force-pump. The suction-pump was known
in the time of Aristotle, who lived about a century before the time of
Archimedes, but the inventor is unknown.

Concerning electricity, the Greeks knew very little. They knew that
amber when rubbed will attract light objects, such as dust or chaff.
Amber was called by the Greeks "electron," because it reflected the
brightness of the sunlight, and their name for the sun was "Elector."
From the Greek name for amber we get our word "electricity."

The Greeks possessed scarcely more knowledge of magnets than of
electricity. In fact, their ideas of magnets cannot be called knowledge,
for they consisted chiefly of legends.

They told of the shepherd Magnes, who, while watching his flock on Mount
Ida, suddenly found the iron ferrule of his staff and the nails of his
shoes adhering to a stone; that, later, this stone was called, after
him, the "Magnes stone," or "Magnet."

They told impossible stories of iron statues being suspended in the air
by means of magnets, and of ships sailing near the magnetic mountains
when every nail and piece of iron in the ship would fly to the mountain,
leaving the ship a wreck upon the waves.




Chapter II

THE AGE OF GALILEO

    Galileo and the Battle for Truth


For eighteen centuries after the time of Archimedes no inventions of
importance were made. Men sought for truth where truth could not be
found. They looked within their mouldy manuscripts and asked, "What do
the great philosophers say ought to happen?" instead of looking at
nature and asking, "What does happen?" And when a man arose who dared to
doubt the authority of the old masters and turn to nature to find out
the truth, all the weapons at the command of the old school were hurled
against him.

Let us, at this distance, blame neither the one side nor the other. The
conflict was inevitable. It was an accident of history that the brunt of
the attack fell upon a man born in Italy in 1564, and that the battle
was fought chiefly in the "Eternal City," from which centuries before
had marched the legions that conquered the world.

The boy, Galileo, who was to become the central figure of the great
conflict, was talented in many ways. In lute-playing his skill excelled
that of his father, who was one of the noted musicians of his day. His
skill in drawing was such that noted artists submitted their work to
him for criticism. He wrote essays on the works of Dante and other
classical writers. He amused his boy companions by constructing toy
machines which, though ingenious, did not always work.

His preference was for mechanics, but, as this subject offered little
prospect of profitable work, he took up the study of medicine in
accordance with his father's wishes.

In his eighteenth year he entered the University of Pisa. Here he found
men who refused to think for themselves, but decided every question by
referring to what the ancient philosophers said. Galileo could not
endure such slavish submission to authority. So strongly did he assert
himself that he was nicknamed "The Wrangler," and, by his wrangling, he
lost a scholarship in the university.

He neglected his medical studies and secretly studied mathematics. His
father, learning of this, consented to his becoming a mathematician.
Thus he followed his bent, though it seemed to lead directly to poverty.

    The Pendulum Clock

It was while a student at the University of Pisa that he discovered a
law of pendulums which makes possible our pendulum clocks. While at his
devotions in the cathedral, he observed the swinging of the bronze lamp
which had been drawn back for lighting. Timing its swinging by means of
his pulse, the only timepiece in his possession, he found that the time
of one swing remained the same, though the length of the swing grew
smaller and smaller. This discovery led to his invention of an
instrument for physicians' use in timing the pulse. About fifty years
later he invented the pendulum clock (Fig. 2).

[Illustration: FIG. 2--GALILEO'S PENDULUM CLOCK
  It had only one hand, which is not shown in the picture.]

Lack of funds compelled him to leave the university without completing
his course. He returned to the parental roof and continued his
scientific studies. The writings of Archimedes were his favorite study.
With Archimedes' famous experiment on King Hiero's crown as a
starting-point, he discovered the laws of floating bodies, which explain
why a ship or other object floats on water, and invented a balance for
weighing objects in water.

But such employment won nothing more substantial than honor and fame.
Food and clothing were needed. For two years he strove without success
to secure employment. At the end of that time he was appointed professor
of mathematics in the University of Pisa at the magnificent salary of
sixty scudi (about sixty-three dollars) per year. "But any port in a
storm; and in Galileo's needy circumstances even this wretched salary
was not to be rejected." Moreover, he could add somewhat to his income
by private tutoring.

    Galileo's Experiment with Falling Shot

While teaching at the University of Pisa, he performed his famous
experiment of dropping from the top of the leaning tower two shot, one
weighing ten pounds, the other one pound. Now, according to Aristotle,
the ten-pound shot should fall in one-tenth the time required by the
one-pound shot. But the assembled company of professors and students saw
the two shot start together, fall together, and strike the ground at
the same instant, and still refused to believe their own eyes. They
continued to affirm that a weight of ten pounds would reach the ground
in a tenth of the time taken by a one-pound weight, because they were
able to quote chapter and verse in which Aristotle assured them that
such is the fact. Thus Galileo made enemies of the other professors, but
for a time they could do nothing more than annoy him.

About this time Galileo incurred the wrath of the Grand Duke of Tuscany,
from whom he had received his appointment. He was commissioned to
examine a machine invented by a nephew of the Grand Duke for the purpose
of cleaning harbors. Galileo plainly said that the machine was
worthless. It was tried, and his opinion proved true. But like the kings
of olden time who killed the bearer of evil tidings even though the
tidings were true, his enemies made his position so unpleasant that he
resigned.

He had neither employment nor money. His father's death occurring about
this time, threw upon him the care of a mother, a worthless brother, and
two sisters. In his distress he sought help from a friend, and secured
an appointment as professor of mathematics in the University of Padua.
His salary was one hundred and eighty florins (about ninety-five
dollars), while other professors received more than ten times as much.

While at Padua, Galileo was busy inventing. He invented the sector,
which is to be found in most cases of mathematical instruments and is
used in certain kinds of drawing. He also invented an air thermometer
(Fig. 3), the first instrument for measuring temperature.

[Illustration: FIG. 3--AN AIR THERMOMETER
  When the air in the bulb grows cooler it contracts, and the air
outside forces the Water up the tube. When the air in the bulb grows
warmer it expands and forces the water down in the tube.]

In 1604 there appeared a new star of great brilliancy. It continued to
shine with varying brightness for eighteen months, and then vanished.
This was a strange event, and Galileo made use of it. He proved that the
new star must lie among the most distant of the heavenly bodies, and
this fact did not agree with Aristotle's view that the heavens are
perfect, and therefore never change. A heated controversy followed, and
Galileo came out boldly in favor of the theory that the earth revolves
about the sun, the prevailing notion then being that the earth does not
move, but that the sun and other heavenly bodies revolve around it.

    The Telescope

In 1609 Galileo learned of a discovery that was to be of great value to
the world, but a source of untold trouble to himself. An apprentice of a
Dutch optician, while playing with spectacle lenses, chanced to observe
that if two of the lenses were placed in a certain position objects seen
through them appeared much nearer. Galileo, learning of this, set to
work to construct a spy-glass, applying his knowledge of light. In one
day he had constructed such an instrument, in which he used two lenses
like the lenses of the modern opera-glass. Thus, while the Dutchman's
discovery was by accident, Galileo's was by reasoning, and was the more
fruitful, as we shall see.

Galileo continued improving his telescope until he had made one which
would magnify thirty times. He was the first to apply the telescope to
the study of the heavenly bodies. The most startling of his discoveries
was that of the moons of the planet Jupiter, which he called new
planets.

This aroused the fury of his enemies, who ridiculed the idea of there
being new planets; "for," they said, "to see these planets they must
first be put inside the telescope." The excitement was intense. Poets
chanted the praise of Galileo. A public fête was held in his honor. One
of his pupils was imprisoned in the tower of San Marco, where he had
gone to make observations with his telescope, and could not escape until
the crowd had satisfied their curiosity. Some of the philosophers
refused to look lest they should see and be convinced.

    Galileo's Struggle

His enemies sought to steal from him the honor of his discoveries. Some
claimed to have made the discoveries before Galileo did. Others claimed
that his discoveries were false, that their only use was to gratify
Galileo's vanity and thirst for gold. In these trying times the
friendship of the great astronomer Kepler warded off some of the most
exasperating attacks.

Galileo's fame spread throughout Europe. Students came in great numbers,
so that he had little leisure left for his own studies. He therefore
decided to leave Padua, and secured an appointment as mathematician and
philosopher to the Grand Duke of Tuscany. This appointment took him to
Florence. It was here that an incident occurred that marked the
beginning of a persecution which continued to the end of his life.

As we read the story of this conflict let us remember that it was not
primarily a conflict between the Roman Catholic Church and Galileo. It
was a conflict of principles. On the one side were arrayed those who
said that men should always believe as the ancient writers did; on the
other, those who said men should think for themselves. In the first
party were most of the university professors and others who dreaded the
introduction of new beliefs, whether in religion or science. In the
second party were Galileo and a small band of devoted followers.

At a dinner at the table of the Grand Duke in Pisa the conversation
turned on the moons of Jupiter. Some praised Galileo. Others condemned
him, saying that the Holy Scriptures were opposed to his theory of the
motion of the earth. A friend reported the incident to Galileo, and he
replied to the arguments of his opponents in a letter which was made
public. No doubt the sting of his sarcasm made his enemies more bitter.
He admitted that the Scriptures cannot lie or err, but this, he said,
does not hold good of those who attempt to explain the Scriptures. In
another letter, he quoted with approval a saying of Cardinal Baronius,
"The Holy Spirit intended to teach us in the Bible how to go to Heaven,
not how the heavens go."

The first shot had been fired. The battle was on, and the Church,
because it possessed the most powerful weapons of attack, was used by
the combined forces to break the power of Galileo's reasoning. He went
to Rome to make his defence, but was commanded by the Holy Office not to
hold or teach that the sun is immovable, and that the earth moves about
the sun.

During another visit to Rome there was shown to Galileo an instrument
which, it was said, would show a flea as large as a cricket. Galileo
recalled that some years before he had so arranged a telescope that he
had seen flies which he said looked as big as a lamb, and were covered
all over with hair. This was the first microscope. Galileo quickly
improved the instrument, and soon his microscopes were in great demand.

In violation of the decree of the Church, to which he had submitted, he
published his most famous work in which he defended the theory that the
earth moves about the sun. The book was the outcome of his life-work,
but the Church believed it dangerous. He was summoned to Rome. Confined
to a sick-bed, he pleaded for delay, which was granted. Before he
recovered, however, the summons was made imperative. He must go to Rome,
or be carried in irons. He went in a litter, carried by servants of the
Grand Duke. In Rome he was to appear before the Inquisition. There he
was treated with a consideration never before accorded to a prisoner of
the Inquisition. Nor was he subjected to torture, as has been stated by
some. He was found guilty of teaching the doctrine that the sun does not
move, and that the earth moves about the sun. He was compelled to
recant, and sentenced to the prison of the Holy Office and, by way of
penance, to repeat once a week for three years the seven penitential
Psalms.

He yielded without reserve to the decree of the Inquisition, renounced
his "errors and heresies," and, with his hand on the Bible, took oath
never again to teach the forbidden doctrine.

And now, though a shattered old man of seventy-four, enjoined to
silence on the chief results of his life-work, nothing could quench his
devotion to science. In these last years, he published a new book which,
with his earlier work, entitles him to be regarded as the founder of the
science of mechanics.

In his study of machines Galileo found that no machine will do work of
itself. Whenever a machine is at work, a man or a horse, or some other
power, is at work upon the machine. In no case will a machine do work
without receiving an equal amount of work.

    Torricelli and the Barometer

Galileo had a pump which he found would not work when the water was
thirty-five feet below the valve. He thought the pump was injured, and
sent for the maker. The maker assured him that no pump would do better.
This led Torricelli, one of Galileo's pupils, to the discovery of the
barometer. Men had said that water rises in a pump because nature abhors
a vacuum. Torricelli believed that air-pressure and not nature's "horror
of a vacuum" is the cause of water rising in a pump. He invented the
barometer to measure air-pressure.

The first barometer was a glass tube filled with quick-silver or mercury
(Fig. 4). The tube was closed at the upper end, and the lower end,
which was open, dipped in a dish of mercury. He allowed the tube to
stand, and saw that the height of the mercury changed. This he believed
was because the air-pressure changed. Wind, Torricelli said, is caused
by a difference of air-pressure, which is due to unequal heating of the
air. For this reason a cool breeze blows from the mountain top to the
heated valley, or from sea to land on a summer day.

[Illustration: FIG. 4--TORRICELLI'S EXPERIMENT]

    Otto Von Guericke and the Air-Pump

About this time a German burgomaster, Otto von Guericke, of Magdeburg,
was performing experiments on air-pressure. The Thirty Years' War had
been raging for thirteen years. The Swedish King, Gustavus Adolphus, had
landed in Germany, and was winning victory after victory over the
imperial troops. Magdeburg had entered into an alliance with the Swedish
King, by which he was granted free passage through the city, while, on
the other hand, he promised protection to the city.

The imperial army under Tilly and Pappenheim laid siege to the city. On
the one side there was hope that Gustavus would arrive in time to effect
a rescue; on the other, a determination to conquer before such aid could
arrive. While Gustavus was on his way to the rescue, Magdeburg was taken
by storm, and the most horrible scene of the Thirty Years' War was
enacted. Tilly gave up the city to plunder, and his soldiers without
mercy killed men, women, and children. In the midst of the scene of
carnage the city was set on fire, and soon the horrors of fire were
added to the horrors of the sword. In less than twelve hours twenty
thousand people perished.

Guericke's house and family were saved, but the sufferings of the city
were not yet ended. In five years the enemy was again before the walls,
and Magdeburg, then in the possession of the Swedes, was compelled to
yield to the combined Saxon and imperial troops. Guericke entered the
service of Saxony, and was again made mayor of the city.

In the midst of these scenes of war, he found time to continue his
studies. He made the first air-pump, and with it performed experiments
which led to some very important results.

The experiments which Guericke made with his air-pump aroused the
attention of the princes, and especially Emperor Ferdinand. Guericke was
called to perform his experiments before the Emperor. The most striking
of these experiments he performed with two hollow copper hemispheres
about a foot in diameter, fitted closely together. When the air was
pumped out, sixteen horses were barely able to pull the hemispheres
apart, though, when air was admitted, they fell apart of their own
weight.

Another experiment which astonished his audience was performed with the
cylinder of a large pump (Fig. 5). A rope was tied to the piston. This
rope was passed over a pulley, and a large number of men applied their
strength to the rope to hold the piston in place. When the air was taken
out of the cylinder, the piston was forced down by air-pressure, and the
men were lifted violently from the ground. This experiment, as we shall
see, was of great importance in the invention of the steam-engine.

[Illustration: FIG. 5--GUERICKE'S AIR-PUMP
  Men lifted from the ground by air-pressure.]

Guericke's study of air-pressure led him to make a water barometer (Fig.
6). This consisted of a glass tube about thirty feet long dipping into a
dish of water. The tube was filled with water, and the top projected
above the roof of the house. On the water in the tube he placed a wooden
image of a man. In fair weather the image would be seen above the
housetop. On the approach of a storm the image would drop out of sight.
This led his superstitious neighbors to accuse him of being in league
with Satan.

[Illustration: FIG. 6--GUERICKE'S WATER BAROMETER
  In fair weather the image appeared above the housetop. When a storm
was approaching the image dropped below the roof into the house.]

The first electrical machine was made by Guericke. This was simply a
globe of sulphur turning on a wooden axle. He observed that when the dry
hand was held against the revolving globe, the globe would attract bits
of paper and other light objects.

    Robert Boyle and the Pressure of Air and Steam

Robert Boyle, in England, improved the air-pump and performed many new
and interesting experiments with it. One of his experiments was to make
water boil by means of an air-pump without applying heat. It is now well
known that water when boiling on a high mountain is not so hot as when
boiling down in the valley. This is because the air-pressure is less on
the mountain top than in the valley. By using an air-pump to remove the
air-pressure, water may be made to boil when it is still quite cold to
the hand.

Boyle compared the action of air under pressure to a steel spring. The
"spring" of the air is evident to us in the pneumatic tire of the
bicycle or automobile. Boyle found that the more air is compressed the
greater is its pressure or "spring," and that steam as it expands
exerts less and less pressure. This is important in the steam-engine.

    Pascal and the Hydraulic Press

It was Blaise Pascal, a Frenchman, who proved beyond the possibility of
a doubt that air-pressure supports the mercury in a barometer, and lifts
the water in a pump (Fig. 7). He had two mercury barometers exactly
alike set up at the foot of a mountain. The mercury stood at the same
height in each. Then one barometer was left at the foot of the mountain,
and the other was carried to the summit, about three thousand feet high.
The mercury in the second barometer then stood more than three inches
lower than at first. As the barometer was carried down the mountain the
mercury slowly rose until, at the foot, it stood at the same height as
at first. The party stopped about half-way down the mountain, allowing
the barometer to rest there for some time, and observing it carefully.
They found that the mercury stood about an inch and a half higher than
at the foot of the mountain. During all this time the height of the
mercury in the barometer which had been left at the foot of the mountain
did not change.

[Illustration: FIG. 7--A LIFT-PUMP
  Air pressing down on the water in the well causes the water to rise in
the pump. The air can do this only when the plunger is at work removing
air or water and reducing the pressure inside the pump.]

It is now known that when a barometer is carried up to a height of nine
hundred feet, the mercury stands an inch lower than at the earth's
surface. For every nine hundred feet of elevation the mercury is lowered
about one inch. In this way the height of a mountain can be measured,
and a man in a balloon or an air-ship can tell at what height he is
sailing. For this purpose, however, a barometer is used that is more
easily carried than a mercury barometer.

Pascal invented the hydraulic press, a machine with which he said he
could multiply pressure to any extent, which reminds us of Archimedes'
saying that, with his own hand, he could move the earth if only he had a
place to stand. Pascal could so arrange his machine that a man pressing
with a force of a hundred pounds on the handle could produce a pressure
of many tons. In fact, a man can so arrange this machine that he can
lift any weight whatever (Fig. 8).

[Illustration: FIG. 8--A SIMPLE HYDRAULIC PRESS
  A one-pound weight holds up a hundred pounds.]

The hydraulic press has two cylinders. One cylinder must be larger than
the other. The two cylinders are filled with a liquid, as water or oil,
and are connected by a tube so that the liquid can flow from one
cylinder into the other. There is a tightly fitting piston in each
cylinder. If one piston has an area of one square inch, and the other
has an area of one hundred square inches, then every pound of pressure
on the small piston causes a hundred pounds of pressure on the large
piston. A hundred pounds on the small piston would lift a weight of ten
thousand pounds on the large piston. But we can see that the large
piston cannot move as fast as the small one does. Though we can lift a
very heavy weight with this machine, we must expect this heavy weight to
move slowly. There must be a loss in speed to make up for the gain in
the weight lifted (Fig. 9). An hydraulic press with belt-driven pump is
illustrated in Fig. 10.

[Illustration: FIG. 9--HOW AN HYDRAULIC PRESS WORKS
  One man with the machine can exert as much pressure as a hundred men
could without the machine. The arrows show the direction in which the
liquid is forced by the action of the plunger _p_. The large piston _P_
is forced up, thus compressing the paper.]

[Illustration: FIG. 10--AN HYDRAULIC PRESS WITH BELT-DRIVEN PUMP]

    Newton

Sir Isaac Newton as a boy did not show any unusual talent. In school he
was backward and inattentive for a number of years, until one day the
boy above him in class gave him a kick in the stomach. This roused him
and, to avenge the insult, he applied himself to study and quickly
passed above his offending classmate. His strong spirit was aroused, and
he soon took up his position at the head of his class.

It was his delight to invent amusements for his classmates. He made
paper kites, and carefully thought out the best shape for a kite and the
number of points to which to attach the string. He would attach paper
lanterns to these kites and fly them on dark nights, to the delight of
his companions and the dismay of the superstitious country people, who
mistook them for comets portending some great calamity. He made a toy
mill to be run by a mouse, which he called the miller; a mechanical
carriage, run by a handle worked by the person inside, a water-clock,
the hand of which was turned by a piece of wood which fell or rose by
the action of dropping water.

At the age of fifteen, his mother, then a widow, removed him from school
to take charge of the family estate. But the farm was not to his liking.
The sheep went astray, and the cattle trod down the corn while he was
perusing a book or working with some machine of his own construction.
His mother wisely permitted him to return to school. After completing
the course in the village school he entered Trinity College, Cambridge.

    Gravitation

It was in the year following his graduation from Cambridge that he made
his greatest discovery--that of the law of gravitation. A plague had
broken out in Cambridge, to escape which Newton had retired to his
estate at Woolsthorpe. Here he was sitting one day alone in the garden
thinking of the wonderful power which causes all bodies to fall toward
the earth. The same power, he thought, which causes an apple to fall to
the ground causes bodies to fall on the tops of the highest mountains
and in the deepest mines. May it not extend farther than the tops of the
mountains? May it not extend even as far as the moon? And, if it does,
is not this power alone able to hold the moon in its orbit, as it bends
into a curve a stone thrown from the hand?

There followed a long calculation requiring years to complete. Seeing
that the results were likely to prove his theory of gravitation, he was
so overcome that he could not finish the work. When this was done by one
of his friends, it was found that Newton's thought was correct--that the
force of gravitation which causes bodies to fall at the earth's surface
is the same as the force which holds the moon in its orbit. As the earth
and moon attract each other, so every star and planet attracts every
other star and planet, and this attraction is gravitation.

    Colors in Sunlight

About the same time that he made his first discoveries regarding
gravitation, he took up the study of light with a view to improving the
construction of telescopes. His first experiment was to admit sunlight
into a darkened room through a circular hole in the shutter, and allow
this beam of light to pass through a glass prism to a white screen
beyond. He expected to see a round spot of light, but to his surprise
the light was drawn out into a band of brilliant colors.

He found that the light which comes from the sun is not a simple thing,
but is composed of colors, and these colors were separated by the glass
prism. In the same way the colors of sunlight are separated by raindrops
to form a rainbow. The colors may be again mingled together by passing
them through a second prism. They will then form a white light.

Suppose that the light of the sun were not composed of different colors,
that all parts of white light were alike, then there would be no colors
in nature. All the trees and flowers would have a dull, leaden hue, and
the human countenance would have the appearance of a pencil-sketch or a
photographic picture. The rainbow itself would dwindle into a narrow
arch of white light; the sun would shine through a gray sky, and the
beauty of the setting sun would be replaced by the gray of twilight
(Fig. 11).

[Illustration: FIG. 11--NEWTON'S EXPERIMENT WITH THE PRISM
  Sunlight separated into the colors of the rainbow. The seven colors
are: violet, indigo, blue, green, yellow, orange, red.]

One of Newton's inventions was a reflecting telescope--that is, a
telescope in which a curved mirror was used in place of a lens. He made
such a telescope only six inches long, which would magnify forty times.

Newton was a member of the Convention Parliament, which declared James
II. to be no longer King of England and tendered the crown to William
and Mary. He was made a knight by Queen Anne in 1705.

His knowledge of chemistry was used in the service of his country when
he was Master of the Mint. It was his duty to superintend the recoining
of the money of England, which had been debased by dishonest officials
at the mint. He did his work without fear or favor.

Once a bribe of £6000 ($30,000) was offered him. He refused it,
whereupon the agent who made the offer said to him that it came from a
great duchess. Newton replied: "Tell the lady that if she were here
herself, and had made me this offer, I would have desired her to go out
of my house; and so I desire you, or you shall be turned out."

Although Newton's discoveries in the world of thought were among the
greatest ever made by man, he regarded them as insignificant compared
with the truth yet undiscovered. He said of himself: "I do not know what
I may appear to the world, but to myself I seem to have been only like a
boy playing on the sea-shore and diverting myself in now and then
finding a smoother pebble or a prettier shell than the ordinary, whilst
the great ocean of truth lay all undiscovered before me."




Chapter III

THE EIGHTEENTH CENTURY

    James Watt and the Steam-Engine


If you had visited the coal-mines of England and Scotland three hundred
years ago, you might have seen women bending under baskets of coal
toiling up spiral stairways leading from the depths of the mines. At
some of the mines horses were used. A combination of windlass and
pulleys made it possible for a horse to lift a heavy bucket of coal.
There came a time, however, when slow and crude methods such as these
could not supply the coal as fast as it was needed. The shallower mines
were being exhausted. The mines must be dug deeper. The demand for coal
was increasing. The supply of coal, it was thought, would not last until
the end of the century. The wood supply was already exhausted. It seemed
that England was facing a fuel famine.

There was only one way out of the difficulty. A machine must be invented
that would do the work of the women and horses, a machine strong enough
to raise coal with speed from the deepest mines. Then it happened that
two great inventors, Newcomen and Watt, arose to produce the machine
that was needed. When the world needs an invention it seldom fails to
appear. It is true of the world, as of an individual, that "Necessity is
the mother of invention."

In the mean time Torricelli had performed his famous barometer
experiment, and Otto von Guericke had astonished princes with proofs of
the pressure of the air. There was no apparent connection between these
experiments and the art of coal-mining, yet these discoveries made
possible the steam-engine which was to revolutionize first the
coal-mining industry and, later, the entire industrial world.

    The First Steam-Engine with a Piston

The first steam-engine with a piston was made by Denys Papin, a
Frenchman. Papin had observed that, in Guericke's experiment,
air-pressure lifted several men off their feet. So he thought the air
could be made to lift heavy weights and do useful work. But how should
he produce the vacuum? His first thought was to explode gunpowder
beneath the piston. The gunpowder engine had been tried by others and
found wanting. He next turned his attention to steam, and discovered
that if the piston were forced up by steam and then the steam condensed,
a vacuum was formed beneath the piston, and air-pressure forced the
piston to descend. If the piston were attached to a weight by a rope
passing over a pulley, then, as the piston descended, it would lift the
weight. Papin's engine consisted simply of a cylinder and piston (Fig.
12). There was no boiler, but the water was placed in the cylinder
beneath the piston. A fire was placed under the cylinder and, as the
water boiled, the steam raised the piston. Then the fire was removed
and, as the cylinder cooled, the steam condensed, and the piston was
forced down by air-pressure. This was a slow and awkward method. The
engine required several minutes to make one stroke.

[Illustration: FIG. 12--PAPIN'S ENGINE
  The first steam-engine with a piston. When the piston _B_ was forced
down by air-pressure, a weight was lifted by means of a rope _TT_
passing over pulleys.]

The principle of Papin's engine was first successfully applied by Thomas
Newcomen. Newcomen was a blacksmith by trade, and his great successor,
Watt, was a mechanic. Thus we see that great discoveries soon become
common property. The blacksmith and the mechanic soon learn to use the
discoveries of the scientist.

    Newcomen's Engine

In the Newcomen engine the piston moved a walking-beam to which was
attached a pump-rod. Steam was used merely to balance the air-pressure
on the piston and allow the pump-rod to descend by its own weight. The
steam was condensed in the cylinder, and the pressure of the air forced
the piston down. Thus the work of raising water in the pump was done by
the air. Newcomen's first engine made twelve strokes a minute, and at
each stroke lifted fifty gallons of water fifty yards. He used this
engine in pumping water from the mines, and also made engines for
lifting coal.

At first the steam was condensed by throwing cold water on the outside
of the cylinder. But one day the engine suddenly increased its speed and
continued to work with unusual rapidity. The upper side of the piston
was covered with water to make the piston air-tight, and it was found
that this water was entering the cylinder through a hole that had worn
in the piston, and this jet of cold water was rapidly condensing the
steam. This was the origin of "jet condensation."

After this steam and water were alternately admitted to the cylinder
through cocks turned by hand. A boy, Humphrey Potter, to whom this work
was intrusted, won fame by tying strings to the cocks in such a way that
the engine would turn the cocks itself and the boy, Humphrey, was free
to play. This device was the origin of valve-gear.[1]

[1] Any device by which a steam-engine operates the valves
which admit steam to the cylinder is called "valve-gear." One form of
valve-gear is the link motion invented by Stephenson. This form will be
described in connection with the locomotive. A simple valve-rod, worked
by an eccentric such as is used on most stationary engines, is also a
form of valve-gear.

Newcomen's engine was extensively used. The tin and copper mines of
Cornwall were deepened. Coal-mines were sunk to twice the depth that had
been possible. But as the mines were deepened the cost of running the
engines increased. The largest engines consumed about $15,000 worth of
coal per year. The Newcomen engine required about twenty-eight pounds of
coal per hour per horse-power, while a modern engine consumes less than
two pounds. Again, because of increased cost, mines were being
abandoned. Such was the situation when James Watt came into the field of
action.

Watt had learned the mechanic's trade in one year in a London shop, and,
because he had not passed through an apprenticeship of seven years, the
Guild of Hammermen, a labor-union of his time, refused him admission,
and this refusal meant no employment. He found shelter, however, in the
University of Glasgow, and was there provided with a small workshop
where he could make instruments for sale.

    Watt's Engine

A small Newcomen engine belonging to the University of Glasgow was out
of repair. London mechanics had failed to make it work. The job was
given to Watt. That he might do a perfect piece of work on this engine,
he made a study of all that was then known relating to steam (Fig. 13).

[Illustration: FIG. 13--THE NEWCOMEN ENGINE, IN REPAIRING WHICH WATT WAS
LED TO HIS GREAT DISCOVERIES
  Preserved in the University of Glasgow.]

He saw that there was a great loss of heat in admitting cold water into
the cylinder to condense the steam, and that, to prevent this loss, the
cylinder must be kept always as hot as the steam that enters it. While
thinking upon this problem the idea came to him that, if connection were
made between the cylinder and a tank from which the air had been
pumped out, the steam would rush into the tank, and might there be
condensed without cooling the cylinder. This was the origin of the
condenser.

We have seen that, in the Newcomen engine, the steam acted only on the
under side of the piston, air acting on the upper side. It occurred to
Watt that the steam should act on both sides of the piston. So he
proposed to put an air-tight cover on the cylinder with a hole and
stuffing-box for the piston to slide through and to admit steam to act
upon it instead of air. Thus he was led to invent the double-acting
engine. The action in the cylinder of Watt's engine was the same as that
of the modern engine.

To save the power of steam, Watt arranged the valve in his engine in
such a way that the steam was cut off from the cylinder when the piston
had made about one-fourth of a stroke. The steam in the cylinder
continues to expand and drive the piston. This device more than doubles
the amount of work that the steam will do (Fig. 14).

[Illustration: FIG. 14--CYLINDER OF WATT'S STEAM-ENGINE
  Arrows show the course of the steam.]

    Horse-Power of an Engine

When horses were about to be replaced by the steam-engine at the mines,
the question was asked: "How many horses will the engine replace?" Tests
were made by Watt and others before him of the rate at which a horse
could work in pumping water or in lifting a weight by means of a pulley.
Watt's experiments showed that "a good London horse could go on lifting
150 pounds over a pulley at the rate of 2-1/2 miles an hour or 220 feet
per minute, and continue the work eight hours a day." This would be
equal to lifting 33,000 pounds one foot high every minute. This rate of
doing work he called a horse-power. It is more than the average horse
can do, but this number was used by Watt that he might give good measure
in his engines. The horse-power of an engine at that time meant the rate
of work in lifting water or coal. Now it means the rate of work done by
the steam upon the piston, so that to find the useful horse-power of an
engine we must deduct the work wasted in friction.

The indicator for measuring the pressure of steam in the cylinder and
the fly-ball governor are also inventions made by Watt (Fig. 15). The
fly-ball governor replaced the throttle-valve which was at first used by
Watt to regulate the speed of his engines. The throttle-valve is still
used on locomotives.

[Illustration: FIG. 15--A FLY-BALL GOVERNOR
  The balls as they rotate regulate the admission of steam to the
cylinder by means of the lever _L_ and the rod _R_.]

At the end of the eighteenth century the steam-engine was full grown. It
remained for the nineteenth century to apply the engine to locomotion on
sea and land, to develop the steam-turbine, and so to increase the power
of the steam-engine that, early in the twentieth century, a
68,000-horse-power engine should speed an ocean liner across the
Atlantic in five days.

    The Leyden Jar

The first electrical invention of practical use was made by Benjamin
Franklin. In Franklin's time great interest in electricity had been
aroused by the strange discovery of a German professor, Pieter van
Musschenbroek, of the University of Leyden. This professor had tried
what he called a new but terrible experiment. He had suspended by two
silk threads a gun-barrel which received electricity from an electrical
machine. From one end of the gun-barrel hung a brass wire. The lower end
of this wire dipped in a jar of water. He held the jar in one hand,
while with the other he tried to draw sparks from the gun-barrel.
Suddenly he received a shock which seemed to him like a lightning
stroke. So violent was the shock that he thought for a moment it would
end his life.

Out of this experiment came the Leyden jar, which for a century and a
half was of no practical use, but which now forms an important part of
every wireless telegraph equipment. The Leyden jar is simply a glass
bottle or jar coated with tin-foil both inside and outside (Fig. 16).
When charged with electricity the jar will hold its charge until the two
coatings are connected by a metal wire or other good conductor of
electricity. A person may receive a strong shock by holding the jar in
one hand and touching a knob connected to the inner coating with the
other hand.

[Illustration: FIG. 16--A LEYDEN JAR]

Popular interest in electricity was aroused by this discovery. The
friction electrical machine and the Leyden jar were simple and easy to
make. People of fashion found them interesting and amusing, the more so
because of the shock felt on taking through the body the discharge from
the "wonderful bottle," and the fact that several persons could receive
the shock at the same instant. On one occasion the Abbé Nollet
discharged a Leyden jar through a line composed of all the monks of the
Carthusian Monastery in Paris. As the line of serious-faced monks a mile
in length jumped into the air, the effect was ridiculous in the extreme.

    Conductors and Insulators

About this time other great electrical discoveries were made. Early in
the century, Stephen Gray discovered that some objects conduct
electricity and others do not. He discovered that, when a glass tube is
electrified by rubbing, it will attract and repel light objects. In the
same way a comb or penholder of rubber may be electrified by rubbing it
on the sleeve. A bit of paper which touches the comb becomes
electrified. Electricity can be transferred from one object to another.
Gray discovered further that contact is not necessary, that a hempen
thread or a wire will carry an electric charge from one object to
another. A silk thread will not carry the electric charge. "Some things
convey electricity," he said, "and some do not, and those which do not
can be used to prevent the electricity escaping from those which do."
Could this obscure inventor have seen a modern telegraph line with the
glass insulators on the poles, which prevent the electric current
escaping from the telegraph wire, he might have realized the importance
of his discovery. He set up a line of hempen thread six hundred and
fifty feet long, and with an electrical machine at one end of the line
electrified a boy suspended from the other end.

    Two Kinds of Electric Charge

A Frenchman, DuFay, while carrying further the experiments of Gray, was
watching a bit of gold-leaf floating in the air. The gold-leaf had been
repelled after contact with his electrified glass tube. Thinking to try
the action of two electrified objects on the gold leaf, he rubbed a
piece of gum-copal and brought it near the leaf. To his astonishment the
leaf, which was repelled by the glass tube, was attracted by the
gum-copal. He repeated the experiment again and again, and each time the
leaf was repelled by the glass and attracted by the gum. He concluded
from this that there are two kinds of electricity, which he named
"vitreous" and "resinous." The two kinds of electric charge were called
by Franklin "positive" and "negative."

Franklin made a battery of Leyden jars, connecting the inner coating of
one to the outer coating of the next throughout the series. In this way
he could get a much stronger spark than with a single jar. On one
occasion he nearly lost his life by taking a shock from his battery of
Leyden jars. He magnetized and demagnetized steel needles by passing
the discharge from his Leyden jars through the needles.

    Franklin's Kite Experiment

The conjecture that lightning is of the same nature as the spark from
the Leyden jar or the electrical machine had gained a hold on the minds
of others before Franklin. In France sparks had been drawn from a rod
ninety-nine feet high, but this did not reach into the clouds. Franklin
determined to send a kite into a thunder-cloud, thinking electricity
from the cloud would follow the string of the kite and could be stored
in a Leyden jar, and used like the charge from an electrical machine. He
had felt the power of a Leyden-jar discharge, and through it had nearly
lost his life. He knew that lightning is far more powerful than any
battery of Leyden jars, and yet to test the truth of his theory, that
lightning is an electrical discharge, he was about to draw the lightning
to his hand. He knew little of conductors of electricity. Whether the
cord would draw little or much of the "electric fire" he knew not. So
far as he knew he was toying with death.

The kite was made of two light strips of cedar placed crosswise, and a
large silk handkerchief fastened to the strips. A sharp wire about a
foot long was fastened to one of the strips. To the lower end of the
cord he attached a key and a silk ribbon. By means of the ribbon he held
the cord to insulate it from his hand. The kite soared into the clouds,
and Franklin and his son stood under a shed awaiting the coming of the
"electric fire" (Fig. 17). Soon the fibres of the cord began to
bristle up. He approached his knuckles to the key. A spark passed. He
brought up a Leyden jar and charged it with electricity from the cloud,
and found that with this charge he could do everything that could be
done with electricity from his machine. He had proved the identity of
lightning and electricity.

[Illustration: FIG. 17--FRANKLIN'S KITE EXPERIMENT
  Taking electricity from the clouds.]

    The Lightning-Rod

Some time before, he had discovered the action of a point in discharging
electricity. He said: "If you fix a needle to the end of a gun-barrel
like a little bayonet, while it remains there the gun-barrel cannot be
electrified so as to give a spark, for the electric fire continually
runs out silently at the point." In the dark you may see a light gather
upon the point like that of a firefly or glow-worm. If the needle is
held in the hand and brought near to an object charged with electricity,
the object is quietly discharged, and a light may be seen at the point
of the needle. This action of points explains the light sometimes seen
on the tops of ships' masts, called by sailors "Saint Elmo's fire," and
perhaps, also, the observation of Cæsar that, in a certain African War,
the spears of the Fifth Roman Legion appeared tipped with fire.

The lightning-rod was the outcome of Franklin's observations, and this
was the first practical invention relating to electricity. A building
may be electrified by an electrified cloud passing over it. If the
building is protected by pointed rods, the electric charge will quietly
escape from the points. The lower ends of the rods must be in the moist
earth below the surface. The lightning-rod has not proved so great a
protection as Franklin supposed it would. He supposed that a
lightning-stroke is a discharge in one direction only; but we now know
that it is a rapid surging back and forth, and this fact accounts for
the failure of the lightning-rods to furnish perfect protection. In
surging back and forth, the lightning may skip from the lightning-rod to
some metal object within the building, as a stove or radiator. The
lightning-rod robbed the thunder-storm of its terrors to the timid, and
in time dispelled the superstition of people who believed that thunder
and lightning are evidence of the wrath of the Deity.

Franklin was the first to propose an answer to the question: What is
electricity? He believed electricity to be a subtle fluid existing in
all objects. If an object has more than a certain amount of this fluid,
it is positively electrified; if less than this amount, it is negatively
electrified.

The "one-fluid" theory of Franklin was soon met by the "two-fluid"
theory proposed by Robert Symmer, for Franklin's theory had failed to
explain why two bodies negatively electrified should repel each other.
According to Symmer, an uncharged body contains an equal quantity of two
different electrical fluids. An excess of one of these produces a
positive charge, an excess of the other a negative charge.

Symmer's experiments are almost ludicrous. He wore two pairs of silk
stockings, and found that white and black silk worn together became
strongly electrified. When the two stockings worn on one foot were
pulled off together, and then separated, they were found to be
electrified, and attracted each other so strongly that a force of about
one pound was required to separate them. The two charges, negative and
positive, could, however, be separated. He thought, therefore, that
there are "two electrical powers," not one, as Franklin believed. His
belief was strengthened by examining a quire of paper through which an
electric spark had passed, and finding that "the edges of the holes were
bent two different ways, as if the hole had been made in the quire by
drawing two threads in contrary directions through it."

There was a long controversy regarding the two theories, and neither
quite gained possession of the field. Each contained some truth, and
each had its weak points. The two had more in common than men at that
time thought.

    Galvani and the Electric Current

Franklin had proven that there is electricity in the atmosphere, and
that lightning is an electric discharge. A widespread interest in the
electricity of the atmosphere followed this discovery. Aloisio Galvani,
a physician in Bologna, Italy, in attempting to learn the effect of
atmospheric electricity on the nerves and muscles of the human body,
made a discovery which led to the electric battery and a knowledge of
electric currents.

Having dissected a frog, he laid it on a table on which stood an
electrical machine. When one of his assistants touched lightly the nerve
of the thigh with the point of a knife while a spark was drawn from the
electrical machine, the muscles contracted violently, as if they were
attacked by a cramp. When he held the knife by the bone handle, there
was no convulsion as there was when he held it by the steel blade.

He next thought it important to find out if lightning would excite
contraction of the muscles. He stretched and insulated a long iron wire
in the open air on the housetop and, as a storm drew near, hung on it a
dissected frog. To the feet he fastened another long iron wire, which
was allowed to dip in the water in the well. "The result," he said,
"came about as we wished. As often as the lightning broke forth, the
muscles were thrown into repeated violent convulsions, so that always,
as the lightning lightened the sky, the muscle contractions and
movements preceded the thunder and, as it were, announced its coming. It
was best, however, when the lightning was strong, or the clouds from
which it broke forth were near the place of the experiment."

He describes his greatest experiment as follows: "After we had
investigated the power of atmospheric electricity in storms, our hearts
burned with the desire to investigate the daily quiet electricity of the
atmosphere. Therefore, as the prepared frogs, hung on an iron railing
which surrounded a hanging garden on our house, with brass hooks
inserted in the spinal cord, fell into convulsions not only when it
lightened, but when the sky was calm and clear, I thought that the cause
of these contractions was the changes in the electricity of the
atmosphere. Then for hours, yes, even days, I observed the animals, but
almost never a movement of the muscles could be seen. At last, tired
with such fruitless waiting, I began to press the brass hooks, which
were fastened in the spinal cord, against the iron railing to see if
such a trick would cause the muscles to contract, and if instead of
changes in the atmospheric electricity any other changes would have any
influence. I observed, indeed, vigorous contractions, but none which
could be caused by the condition of the atmosphere."

It was pressing the brass hook against the iron railing, thus forming an
electric battery, that caused electricity to pass through the muscles of
the frog. Galvani did not know that he had discovered a new source of
electricity. He never arrived at a correct explanation of his results,
and never knew the value of his discovery.

    Volta and the Electric Battery

It was left for Alexander Volta to show that, in Galvani's experiment,
the muscles of the frog, together with the brass hook and the iron
railing, formed an electric battery. Volta showed that an electric
charge can be produced merely by bringing two different metals into
contact. He found that, if he placed copper and zinc in sulphuric acid,
or a solution of common salt, he could, produce a continuous flow of
electricity (Fig. 18).

[Illustration: FIG. 18--VOLTA EXPLAINING HIS ELECTRIC BATTERY TO
NAPOLEON BONAPARTE
  From a painting. Photo by Dubray.]

In the beginning of the year 1800 Volta made the first electric battery
(Fig. 19). It was made of copper and zinc disks placed alternately, with
a piece of wet cloth above each pair of disks. With his column of disks
he could obtain a strong shock; indeed, many shocks, one after the
other. This first battery of Volta's was a form of "dry battery." Later
Volta devised his "crown of cups," a form of wet battery similar to
some batteries in use to-day. Each cup contained a strip of copper and a
strip of zinc in dilute sulphuric acid.

[Illustration: FIG. 19--THE FIRST ELECTRIC BATTERY
    No. 1--A battery of one hundred pairs of copper and zinc disks.
    No. 2--Two such batteries connected.
  By permission of the Italian Institute of Graphic Arts, Bergamo.]

Volta did not know the real use of the liquid in his battery, nor that
the strength of the current depends on the rate at which the metal is
dissolved by the acid; but he had discovered the electric current, and
with this discovery began a new era in electrical invention.




Chapter IV

FARADAY AND THE FIRST DYNAMO


Michael Faraday, a London newsboy, the son of a blacksmith, became the
inventor of the dynamo, and prepared the way for the wonderful
electrical inventions of the nineteenth century. He began his career as
a book-binder's apprentice, employing his spare moments in reading the
books he was binding. One of these books led him to make some simple
experiments in chemistry. He also made an electrical machine, first with
a glass bottle, and afterward with a glass cylinder.

While an apprentice he wrote to his young friend, Benjamin Abbott: "I
have lately made a few simple galvanic experiments, merely to illustrate
to myself the first principles of the science. I was going to Knight's
to obtain some nickel, and bethought me that they had malleable zinc. I
inquired, and bought some--have you seen any yet? The first portion I
obtained was in the thinnest pieces possible. It was, they informed me,
thin enough for the electric stick. I obtained it for the purpose of
forming disks with which and copper to make a little battery. The first
I completed contained the immense number of seven pairs of plates!!! and
of the immense size of halfpence each!!!!!! I, sir, I my own self, cut
out seven disks of the size of half pennies each! I, sir, covered them
with seven halfpence, and I interposed between them seven, or rather
six, pieces of paper soaked in a solution of muriate of soda (common
salt). But laugh no longer, dear A., rather wonder at the effects this
trivial power produced."

This tiny battery made of half pennies with zinc disks and salt solution
would decompose a certain solution which Faraday tested. A larger
battery made of copper and zinc disks with salt solution would decompose
water from the cistern. When the wires from the larger battery were put
in the cistern-water he saw a dense white cloud descending from the
positive wire, and bubbles rising from the negative wire. This action
continued until all the white substance was taken out of the water.

Because of his interest in science, young Faraday attracted the
attention of a Mr. Dance, a member of the Royal Institution and a
customer of his master, Mr. Riebau. Through the kindness of Mr. Dance he
heard four lectures by Sir Humphry Davy. He took notes on the lectures,
wrote them out carefully, and added drawings of the apparatus. These
notes he sent to Davy with a letter expressing the wish that he might
secure employment at the Royal Institution. In a short time, after a
warning from Sir Humphry that he had better stick to his business of
book-binding, that "Science is a harsh mistress," his wish was granted,
and we find him cleaning and caring for apparatus in the Royal
Institution and assisting Davy in preparing for his lectures.

    Count Rumford

Our story now takes us back to the time of the American Revolution. In
America, we find a young man of nineteen, Benjamin Thompson by name,
serving as major in the Second Regiment of New Hampshire. The
appointment of so young a man as major, and his evident hold on the
governor's favor, aroused the jealousy of the older officers. He was
accused of being unfriendly to the cause of liberty. He denied the
charge, and was acquitted by the committee of the people of Concord. A
mob gathered round his house, but he escaped. Driven from his refuge in
his mother's home, he fled to England, leaving his wife and child.
Appointed lieutenant-colonel in the British Army, he returned to America
and fought against his former friends.

The war having ended, he returned to England, thence to the Continent,
intending to take part in an expected war between Austria and Turkey. A
chance meeting with a Bavarian prince, Maximilian, changed the course of
his life. This prince, while commanding on parade, saw Thompson among
the spectators mounted on a fine English horse, and addressed him.
Thompson informed him that he came from serving in the American war. The
prince, pointing to a number of his officers, said: "These gentlemen
were in the same war, but against you. They belonged to the Royal
Regiment of Deux Ponts, that acted in America under the orders of Count
Rochambeau." Thompson dined with the prince and French officers. They
conversed of war and the battles in which they met. The prince,
attracted to the colonel, induced him to pass through Munich, and gave
him a letter to his uncle, the Elector of Bavaria.

It was in Bavaria, the country to which such unexpected turns of fortune
led him, that his greatest work was done. He entered the service of the
Duke of Bavaria as aide-de-camp. It was his aim while in the service of
the Bavarian Government to better the condition of the people. He
introduced reforms in the army, used the soldiers to rid the country of
beggars and robbers, and took steps to provide for the infirm and find
employment for the strong, his motto being that people can best be made
virtuous when first made happy.

A Military Workhouse was opened for the beggars, and a House of Industry
for the poor. A Military Academy was formed with a view to the free
education of young people of talent for the public service. He became
absorbed in the one aim of helping the poor. So thorough was his
devotion to the people, and so deeply did he win their affection, that
when he was dangerously ill a multitude of hundreds went in procession
to the church to make public prayers for his recovery.

He saw that the poor may be helped by teaching them to save, and in
nothing is there greater need of saving than in fuel and heat. In the
kitchens of the Military Academy and the House of Industry he carried
out a series of experiments on the economy of fuel, and succeeded in
greatly reducing the amount of fuel needed for cooking the food. He did
this by using a "closed fireplace," the forerunner of the stove. The
closed fireplace was in reality a brick stove, and was a great
improvement over the open chimney fireplaces then in common use. He
made the covers of the cooking utensils double, to save the heat, for he
had found that heat cannot escape through confined air.

Benjamin Thompson was knighted by George III., and in 1791 he was made a
Count of the Holy Roman Empire, and is known to the world of science as
Count Rumford.

    Count Rumford's Experiment with the Cannon

While in the service of the Duke of Bavaria, it became his duty to
organize the field artillery. To provide cannon for this purpose, he
erected a foundry and machine-shops. Being alert for any unusual fact
relating to heat, he observed the very high temperature produced by the
boring of the cannon. He was eager to learn how so much heat could be
produced. For this purpose he took a cannon in the rough, as it came
from the foundry, fixed it in the machine used for boring, and caused
the cannon to be turned by horses while a blunt borer was forced against
the end of the cannon. He first tested the temperature of the metal
itself as it turned. Then he surrounded the end of the cannon with water
in an oblong box fitted water-tight (Fig. 20).

[Illustration: FIG. 20--COUNT RUMFORD'S EXPERIMENT WITH THE CANNON,
MAKING WATER BOIL WITHOUT FIRE
  The horses make the water boil by walking around the track; the work
the horses do is changed into heat by the friction of the drill.]

The cannon had been turning but a short time when he found by putting
his hand in the water that heat had been produced. In two hours and
thirty minutes the water actually boiled. Astonishment was expressed in
the faces of the bystanders on seeing so large a quantity of water
heated and actually made to boil without any fire.

"Heat," Count Rumford said; "may thus be produced merely by the strength
of a horse, and, in case of necessity, this heat might be used in
cooking victuals. But no circumstance can be imagined in which there is
any advantage in this method of procuring heat, for more heat might be
obtained by burning the fodder which the horse would eat." The meaning
of this last remark was not understood until the time of Robert Mayer,
about fifty years later. Rumford had found that the work of a horse can
produce heat, and heat, in a steam-engine, can do the work of a horse.
Thus surely, though slowly, men were learning of the forces that move
the world and do man's bidding.

Count Rumford, true to his adopted land, returned to London and became
the founder of the Royal Institution in which Faraday and his successors
have achieved such marvellous results. He believed that the poor can be
helped in no better way than by giving them knowledge, so that they can
better their own condition. For this purpose he founded the Royal
Institution. Here he intended that men skilled in discovery should gain
new knowledge that would add to the comfort and happiness of the people.

    Davy

In the English coal-fields many accidents due to the burning of
fire-damp had occurred. Fire-damp is caused by gas issuing from the
coal. On the approach of a flame this gas catches fire, and as it burns
it produces a violent wind, driving the flame before it through the
mine. Miners were scorched to death, suffocated, or buried under ruins
from the roof. Hundreds of miners had been killed. No means of lighting
the mines in safety had been devised. Sir Humphry Davy, Professor of
Chemistry in the Royal Institution, was appealed to. After many
experiments he devised a "safe lamp," which was a common miner's lamp
enclosed in a wire gauze. This proved a perfect protection from
fire-damp, and the Davy safety lamp has been used by miners the world
over for more than a century.

But Davy's best work was with the electric battery. Some of the facts
most familiar to us were discovered by him. Volta had contended that the
contact of the metals in a battery produces a current, that the liquid
merely carries the electricity from one metal plate to the other. But
Davy proved that there can be no current without chemical action.
Whenever we put two metals in an acid or other solution that will
dissolve one metal faster than the other, and connect the metals with a
wire, an electric current is produced. If we use water with silver and
gold, there is no current, because water will not dissolve either the
silver or the gold.

Davy discovered the metal, potassium, by means of his electric battery.
Potassium is found in common potash and saltpetre, and, when separated,
is a very soft metal. The newly discovered metal aroused great interest
in other countries. When Napoleon heard of it, he inquired impetuously
how it happened the discovery had not been made in France. On being told
that in France there had not been made an electric battery of sufficient
power, he exclaimed: "Then let one be instantly made without regard to
cost or labor." His command was obeyed, and he was called to witness the
action of the new battery. Before any one could interfere he placed the
ends of the wires under his tongue and received a shock that nearly
deprived him of sensation. On recovering he left the laboratory without
a word, and was never afterward heard to refer to the subject.

Davy made many great discoveries, but the greatest was his discovery of
Faraday.

       *       *       *       *       *

A journey on the Continent with Davy was an event in the life of
Faraday, who up to that time had never to his own recollection travelled
twelve miles from London. On this journey he met Volta, whom he
describes as "an hale elderly man, very free in conversation." He
visited the Academy del Cimento, in Florence, and wrote: "Here was much
to excite interest; in one place was Galileo's first telescope, that
with which he discovered Jupiter's satellites. It was a simple tube of
wood and paper, about three and a half feet long, with a lens at each
end. There was also the first lens which Galileo made. It was set in a
very pretty frame of brass, with an inscription in Latin on it."

Faraday crossed the Alps and the Apennines, climbed Vesuvius, visited
Rome, and _saw a glow-worm_. The last he thought as wonderful as the
first.

Shortly after his return to London he fell in love. Now, Faraday had
determined that he would not be conquered by the master passion. In
fact, he had written various aspersions on love, of which the following
is a sample:

    "What is the pest and plague of human life?
    And what the curse that often brings a wife?
                    'Tis Love.

    What is't directs the madman's hot intent,
    For which a dunce is fully competent?
    What's that the wise man always strives to shun,
    Though still it ever o'er the world has run.
                    'Tis Love."

But he reckoned not with his own heart. It is not long until we find him
writing to Miss Sarah Barnard, a bright girl of twenty-one: "You have
converted me from one erroneous way, let me hope you will attempt to
correct what others are wrong.... Again and again I attempt to say what
I feel, but I cannot. Let me, however, claim not to be the selfish being
that wishes to bend your affections for his own sake only. In whatever
way I can minister to your happiness, either by close attention or by
absence, it shall be done. Do not injure me by withdrawing your
friendship or punish me for aiming to be more than a friend by making me
less."

They were married and lived in rooms at the Royal Institution. No poet
ever loved more tenderly than Faraday. Truly, science does not dry up
the heart's blood. At the age of seventy-one he wrote to his wife while
absent from home for a few days: "Remember me; I think as much of you as
is good for either you or me. We cannot well do without each other. But
we love with a strong hope of love continuing ever."

    Faraday's Electrical Discoveries

Now we shall turn to Faraday's electrical discoveries and inventions.
Men had long known that, in houses that have been struck by lightning,
steel objects such as knives and needles are sometimes found to be
magnetized. Ships struck by lightning had found their compass-needles
pointing south instead of north, or wandering in direction and
worthless. Men had wondered how an electrical discharge could magnetize
steel. They had tried the spark of the electrical machine with no
definite result. Franklin, in his experiment of magnetizing a steel
needle by passing an electric spark through it, could not tell before
the spark was passed through the needle which end would be the north
pole. There was no seeming connection between the direction of the
electric discharge and the polarity of the needle. After the discovery
of the electric battery, men tried to discover a relation between the
electric current and magnetism.

    Oersted and Electromagnetism

The first success in this direction was achieved by Hans Christian
Oersted, a native of Denmark. Poverty impelled his father to take him
from school at the age of twelve and place him in an apothecary's shop.
The boy, Hans, found delight in the chemical work of the apothecary. His
eagerness to learn and the pressure of poverty led him to neglect the
usual sports of boyhood and devote his leisure time to reading and
study. Again he entered school, and, though paying his way by his own
work, he graduated with honor from the University of Copenhagen. He was
appointed Professor of Physics in this university, and here he made his
first great discovery in electromagnetism.

After working for seven years to discover a relation between current
electricity and magnetism, he made a discovery which proved to be the
first step in the invention of the dynamo. He was using a magnetic
compass, which is a small magnetic needle balanced on a steel point. The
needle points nearly north and south unless disturbed by a magnet
brought near it. He had tried to find if a wire through which a current
is flowing would disturb the compass as a magnet does. He had tried
placing the wire east and west, thinking the compass-needle would follow
the wire as it does a magnet. One day, while lecturing to his students,
it occurred to him for the first time to place the wire north and south
over the compass-needle. He was surprised and perplexed as he did so to
see the needle swing round and point nearly east and west (Fig. 21). On
reversing the current the needle swung in the opposite direction. He had
discovered the magnetic action of an electric current. It was learned
soon afterward that a coil of wire with an electric current flowing
through it acts like a magnet, and that a current flowing around a bar
of soft iron makes the iron a magnet (Figs. 22 and 23).

[Illustration: FIG. 21--OERSTED'S EXPERIMENT
  An electric current flowing over the compass-needle toward the north
causes the needle to turn until it points nearly west.
  By permission of Joseph G. Branch.]

[Illustration: FIG. 22.--A COIL WITH A CURRENT FLOWING THROUGH IT ACTS
LIKE A MAGNET
  The coil is picking up iron filings.]

[Illustration: FIG. 23--A BAR OF SOFT IRON WITH A CURRENT FLOWING AROUND
IT BECOMES A MAGNET]

    Ampère

The news of Oersted's discovery aroused great interest throughout
Europe. Soon after its announcement in France, André Marie Ampère made a
discovery of equal importance. Oersted had discovered electromagnetism.
Ampère discovered electrical power or motion produced by an electrical
current.

The youth of Ampère was passed amid the stormy scenes of the French
Revolution. His father had moved from his country home to Lyons and
become a justice of the peace. In the destruction of the city of Lyons
during the Reign of Terror he lost his head under the guillotine.

The blow was too great for Ampère, then a youth of eighteen. He had been
a precocious child, advanced beyond his years in all the studies of the
schools. But now his strong mind failed. For a year he wandered about
mechanically piling up heaps of sand or gazing upon the sky. Then his
mental power returned, and he took up with eagerness the study of botany
and poetry.

He became a professor in the Polytechnic School in Paris, and it was
while teaching in this school that he made his great discoveries. He
found that two coils of wire can be made to attract or repel each other
by an electric current. If the current flows through the two coils in
the same direction, they attract each other (Fig. 24). If the current
flows in opposite directions through the coils, they repel each other
(Fig. 25). This is not very strange to us, for we know that a coil with
a current flowing through it acts just like a magnet. Each coil then has
a north pole and a south pole. If the coils are placed so that the two
north poles or the two south poles are together, they will repel each
other. If the north pole of one coil is near the south pole of the
other, they will attract each other.

[Illustration: FIG. 24--TWO COILS WITH CURRENTS FLOWING IN SAME
DIRECTION ATTRACT EACH OTHER]

[Illustration: FIG. 25--TWO COILS WITH CURRENTS FLOWING IN OPPOSITE
DIRECTIONS REPEL EACH OTHER]

Ampère believed that electric currents are flowing around within the
earth, and that the earth has a north and a south magnetic pole for the
same reason that a coil of wire has magnetic poles; that these poles are
caused by the currents flowing around in the earth just as the poles of
the coil are caused by the current flowing around in the coil.

We do honor to the name of Ampère whenever we measure an electric
current, for electric currents are measured in "amperes."

    Arago

Another important discovery was made by a young Frenchman, François
Arago, within a year of the time when Oersted and Ampère made their
discoveries. The three great discoveries of these men were made in the
years 1819 and 1820. The youth of Arago was full of adventure. He had
assisted in making a survey in the Pyrenees, the haunt of daring
robber-bands. Twice in his cabin he was visited by a chief of a
robber-band who claimed to be a custom-house guard. On the second visit
he said to the robber: "Your position is perfectly known to me. I know
that you are not a custom-house guard. I have learned that you are the
chief of the robbers of the country. Tell me whether I have anything to
fear from your confederates." The robber replied: "The idea of robbing
you did occur to us; but, on the day that we molested an envoy from the
French, they would direct against us several regiments of soldiers, and
we are not so strong as they. Allow me to add that the gratitude which I
owe you for the night's shelter is your surest guarantee."

At a later time, when war between Spain and France was threatened, he
was accused of being a spy, and a mob was formed to put him out of the
way. He escaped in disguise through the midst of the mob and boarded a
Spanish ship. He was carried to Morocco, ran the gantlet of bloodthirsty
Mussulmans in Algiers, escaped death by a hair's-breadth, and through it
all clung to the papers which recorded the results of the survey in the
mountains, and delivered them in safety to the office of the Bureau of
Longitude in Paris.

Arago made a discovery which, with those of Oersted and Ampère, prepared
the way for Faraday's great electrical discoveries and the invention of
the dynamo. He found that a plate of copper whirling above or below a
magnetic needle will draw the needle after it (Fig. 26). He could make
the speed of the whirling copper plate so great that the needle would
whirl rapidly, following the copper plate. Faraday was the first to
explain Arago's experiment.

[Illustration: FIG. 26--ARAGO'S EXPERIMENT
  When the copper plate whirls the magnet whirls also, though it does
not touch the copper plate.]

    Faraday's First Electric Motor

Faraday's first electrical discovery was made soon after that of Arago.
Oersted had proven that an electric current acts on a magnet. The magnet
turns at right angles to the wire. Faraday saw that this is because the
north pole of the magnet tries to go round the wire in one direction,
and the south pole tries to go round in the opposite direction. He
placed a magnet on end in a dish of mercury, with one pole of the magnet
above the mercury, and found that the magnet would spin round a wire
carrying a current. When the current acts on one pole of the magnet
only, the magnet spins round the wire (Fig. 27). So Faraday's first
electrical discovery prepared the way for the electric motor.

[Illustration: FIG. 27--ONE POLE OF A MAGNET SPINS ROUND A WIRE THROUGH
WHICH AN ELECTRIC CURRENT FLOWS]

    An Electric Current Produced by a Magnet

He had written in his note-book: "Convert magnetism into electricity."
An electric current would magnetize iron. Would not a magnet produce an
electric current? This was his problem.

He connected a coil of wire to an instrument that would tell when a
current was flowing, and placed a magnet in the coil. Others had
claimed, and Faraday at first believed, that a current would flow while
the magnet lay quiet within the coil. But Faraday was alert for the
unexpected, and the unexpected happened. For an instant, as he thrust
the magnet into the coil, his instrument showed that a current was
flowing. Again, as he drew the magnet quickly from the coil, a current
flowed, but in the opposite direction (Fig. 28). From this simple
experiment has grown the alternating-current machinery by which the
power of Niagara is made to light cities and drive electric cars at a
distance of many miles.

[Illustration: FIG. 28--WHEN A MAGNET IS THRUST INTO A COIL OF WIRE IT
CAUSES A CURRENT TO FLOW IN THE COIL, BUT THE CURRENT FLOWS ONLY WHILE
THE MAGNET IS MOVING
  Drawing reproduced by permission of Joseph G. Branch.]

A friend of Faraday, on learning of this discovery, wrote the following
impromptu lines:

    "Around the magnet Faraday
    Was sure that Volta's lightnings play.
      But how to draw them from the wire?
    He took a lesson from the heart:
    'Tis when we meet, 'tis when we part,
      Breaks forth the electric fire."

A magnet will produce an electric current in a wire, but only when the
magnet or the wire is in motion.

    Detecting and Measuring an Electric Current

The instrument which Faraday used to detect a current was derived from
Oersted's experiment. When a current flows in a north-and-south
direction over a compass-needle, the needle swings round. When the
current stops flowing the needle swings back to the north-and-south
position. The effect on the needle is stronger if the current flows
through a coil of wire and the coil is placed in a north-and-south
position around the needle (Fig. 29). The stronger the current flowing
through the coil the farther the needle will turn from the
north-and-south position.

[Illustration: FIG. 29--A COIL OF WIRE AROUND A COMPASS-NEEDLE
  The needle tells when a current is flowing, and how strong the current
is.]

The coil and the needle together are called a galvanometer, and may be
used to tell when a current is flowing, and also to indicate the
strength of the current.

    An Electric Current Produced by the Magnetic Field of Another Current

Faraday had found that a current flowing around a piece of iron will
make the iron a magnet, and that a magnet in motion will cause a current
to flow in a wire. It seemed to him that a second wire placed near the
first should have a current produced in it without the presence of iron.
He wound two coils of copper wire upon the same wooden spool. The wire
of the two coils he separated with twine and calico. One coil was
connected with a galvanometer, the other with a battery of ten cells,
yet not the slightest turning of the needle could be observed. But he
was not deterred by one failure. He raised his battery from ten cells to
one hundred cells, but without avail. The current flowed calmly through
the battery wire without producing, during its flow, any effect upon the
galvanometer. During its flow was the time when an effect was expected.

Again the unexpected happened. At the instant of making contact with the
battery there was a slight movement of the needle. When the contact was
broken, another slight movement, but in the opposite direction to the
first (Fig. 30). The current in one wire caused a current to flow in the
other, but the current in the second wire continued for an instant only
at the making and breaking of the contact with the battery. This was the
beginning of the induction-coil used to-day in wireless telegraphy.

[Illustration: FIG. 30--FARADAY'S INDUCTION-COIL
  Starting and stopping the battery current in the primary coil causes a
changing magnetic field, and this causes a current to flow in the
secondary coil.
  Drawing reproduced by permission of Joseph G. Branch.]

What was the secret of it? Simply this: that a current in one wire will
cause a current to flow in another wire near it, but only while the
current in the first wire is changing. That is, at the instant when the
first wire is connected to the battery, or its connection broken, a
current is induced in the second wire. There is no battery or other
source of current connected to the second wire; but a current flows in
this wire because it is near a wire in which a current is rapidly
starting and stopping. When these two wires are wound in coils, together
they form an induction-coil. The wire which we have called the first
wire forms the "primary" coil, and the one we have called the second
wire forms the "secondary" coil. By repeatedly making and breaking the
circuit in the primary coil we get an alternating current in the
secondary coil. Fig. 31 is from a photograph of some of the coils
actually used by Faraday.

[Illustration: FIG. 31--HISTORICAL APPARATUS OF FARADAY IN THE ROYAL
INSTITUTION
  Some of Faraday's transformer coils are shown here. The instrument on
the left in a glass case is his galvanometer.]

    Faraday's Dynamo

To invent a new electrical machine was Faraday's next aim. Arago's disk
of copper whirling near a magnet had a current induced in it, so Faraday
thought. It was the action of this induced current which caused the
magnet to follow the whirling disk. Could the current in Arago's disk be
collected and caused to flow through a wire? He placed a copper disk
between the poles of a magnet. One galvanometer wire passed around the
axis of the disk, the other he held in contact with the edge. He whirled
the disk. The galvanometer needle moved. A current was flowing in the
disk as it whirled. The current from the whirling disk flowed through
the galvanometer. Faraday had discovered the dynamo (Fig. 32).

[Illustration: FIG. 32--FARADAY'S FIRST DYNAMO
  A current flows in the copper disk as it whirls between the poles of
the magnet.
  By permission of Joseph G. Branch.]

All this work occupied but ten days in the autumn of 1831, though years
of preparation had gone before. In these ten days the foundation was
laid for the induction-coil, modern dynamo-electric machinery, and
electric lighting. Fig. 33 shows the laboratory in which Faraday did
this work.

[Illustration: FIG. 33--FARADAY'S LABORATORY, WHERE THE FIRST DYNAMO WAS
MADE
  From the water-color drawing by Miss Harriet Moore.]

Faraday continued to explore the field opened up before him. In one
experiment two small pencils of charcoal lightly touching were connected
to the ends of a secondary coil. A spark passed between the charcoal
points when the primary circuit was closed. This was the first
transformer producing a tiny electric light (Fig. 34).

[Illustration: FIG. 34--THE FIRST TRANSFORMER]

Faraday discovered the induction-coil, the dynamo, and the transformer,
and he showed that, in each of these, it is magnetism which produces the
electric current. He had discovered the secret when he obtained a
current by thrusting a magnet into a coil of wire. The space about a
magnet in which the magnet will attract iron he called the "magnetic
field" (Figs. 35 and 36). In every case of magnetism causing an electric
current to flow in a coil of wire, the coil is in a magnetic field, and
the magnetic field is changing--that is, the magnetic field is made
alternately stronger and weaker, or the coil moves across the magnetic
field. The point is that magnetism at rest will not produce an electric
current. There must be a changing magnetic field or motion. In Faraday's
dynamo a copper disk whirled between the poles of a magnet and the
whirling of the disk in the magnetic field caused an electric current.
In the modern dynamo it is the whirling of a coil of wire in a magnetic
field that causes a current to flow. In the induction-coil it is the
change in the magnetic field that causes a current to flow in the
secondary coil. A coil of wire with an electric current flowing through
it will attract iron like a magnet. The primary coil with a current from
a battery flowing through it acts in all respects like a magnet; but as
soon as the current ceases to flow the magnetic field disappears--the
coil is no longer a magnet. When we make and break the connection
between the primary coil and the battery, then, we repeatedly make and
destroy the magnetic field, and this changing magnetic field causes a
current to flow in the secondary coil. The induction-coil is one form of
transformer. We shall see later how the dynamo and the transformer
developed in the nineteenth century.

[Illustration: FIG. 35--THE "MAGNETIC FIELD" IS THE SPACE AROUND A
MAGNET IN WHICH IT WILL ATTRACT IRON
  The iron filings over the magnet arrange themselves along the "lines of
force."]

[Illustration: FIG. 36--MAGNETIC FIELD OF A HORSESHOE MAGNET]

When a boy, Faraday had passed the current from his little battery
through a jar of cistern-water, and saw in the water a "dense white
cloud" descending from the positive wire, and bubbles arising from the
negative wire. Something was being taken out of the water by the
electric current. When he tried the experiment later in his laboratory,
he found that, whenever an electric current is passed through water,
bubbles of two gases, oxygen and hydrogen, rise through the water. He
found that if the current is made stronger the bubbles are formed
faster. The water in time disappears, for it has been changed or
"decomposed" into the two gases.

It was the current from a battery that would decompose water. The
electricity from the electrical machine would do other things that he
had never seen a battery current do. "Do the battery and the electrical
machine produce different kinds of electricity, or is electricity one
and the same in whatever way it is produced?" This was the query that
troubled him. The answer to this question had been so uncertain that the
effect of the voltaic battery had been termed "galvanism," while that of
the friction machine retained the name "electricity."

Faraday tried many experiments in searching for an answer to this
question. He found that the electricity of the machine will produce the
same effect as that of a battery if the machine is compelled to
discharge slowly. An electrical machine or a battery of Leyden jars can
be made to give out an electric current, and this current will affect a
magnetic needle in the same way that a battery current will. It will
magnetize steel. If passed through water, it will decompose the water
into the two gases oxygen and hydrogen. In short, a current from an
electrical machine or a Leyden jar will do everything that a current
from an electric battery will do. Faraday caused the Leyden jar to give
a current instead of a spark by connecting the two metal coatings with a
wet string. On the other hand, the discharge from a powerful electric
battery will produce a spark and affect the human nerves in the same way
as the discharge from the electrical machine. The same effects may be
obtained from one as from the other.

In the discharge from the machine, a small quantity of electricity is
discharged under high pressure, as water may be forced through a small
opening by very high pressure. The voltaic cell, on the other hand,
furnishes a large quantity of electricity at low pressure, as a street
may be flooded by a broken water-main though the pressure is low. In
fact, the quantity of electricity required to decompose a grain of water
is equal to that discharged in a stroke of lightning, while the action
of a dilute acid on the one-hundredth part of an ounce of zinc in a
battery yields electricity sufficient for a powerful thunder-storm.

Many tests were made, and the result was a convincing proof that
electricity is the same whatever its source, the different effects being
due to difference in pressure and quantity. "But in no case," said
Faraday, "not even in those of the electric eel and torpedo, is there a
production of electric power without something being used up to supply
it."

Faraday's professional work would have made him wealthy. In one year he
made £1000 ($5000), and the amount would have increased had he sold his
services at their market value. But then there would have been no
Faraday the discoverer. The world would have had to wait, no one knows
how long, for the laying of the foundations of electrical industries. He
chose to give up wealth for the sake of discovery. He gave up
professional work with the exception of scientific adviser to Trinity
House, the body which has charge of Great Britain's lighthouse service.
Nor did he carry his discoveries to the point of practical application.
As soon as he discovered one principle, he set out in pursuit of others,
leaving the practical application to the future.

Faraday loved the beauty of nature. The sunset he called the scenery of
heaven. He saw the beauty of electricity, which he said lies not in its
mystery, but in the fact that it is under law and within the control of
the human intellect.

    A Wonderful Law of Nature

Not long after Faraday made his first dynamo, Robert Mayer, a physician
from Germany, was making a voyage to the East Indies which proved to be
a voyage of discovery. He had sailed as the ship's physician, and after
some months an epidemic broke out among the ship's company. In his
treatment he drew blood from the veins of the arms. He was startled to
see bright-red blood issue from the veins. He might almost have believed
that he had opened an artery by mistake. It was soon explained to him by
a physician who had lived long in the tropics that the blood in the
veins of the natives, and of foreigners as well, in the tropics is of
nearly the same color as arterial blood. In colder climates the venous
blood is much darker than the arterial.

He reasoned upon this curious fact for some time, and came to the
conclusion that the human body does not make heat out of nothing, but
consumes fuel. The fuel is consumed in the blood, and there the heat is
produced. In the tropics less heat is needed, less fuel is consumed, and
therefore there is less change in the color of the blood.

When a man works he uses up fuel. If a blacksmith heats a piece of iron
by hammering, the heat given to the iron and the heat produced in his
body are together equal to the heat of the fuel consumed in his blood.
The work a man does, as well as the heat of his body, comes from the
burning of the fuel in his blood.

What is true of a man is true of an engine. The work the engine does, as
well as the heat it produces, comes from the heat of the fuel in the
furnace. Mayer found that one hundred pounds of coal in a good working
engine produces the same amount of heat as ninety-five pounds in an
engine that is not working. In the working engine the heat of the five
pounds of coal is used up in the work of running the engine, and
therefore does not heat the engine. Heat that is used in running the
engine is no longer heat, but work. So Mayer said the heat is not
destroyed, but only changed into work. He said, further, that the work
of running the engine may be changed again into heat.

Mayer's theory was opposed by many scientific men of Europe. One great
scientist said to him that if his theory were correct water could be
warmed by shaking. He remembered what the helmsman had remarked to him
on the voyage to Java, that water beaten about by a storm is warmer than
quiet sea-water; but he said nothing. He went to his laboratory, tried
the experiment, and some weeks later returned, exclaiming: "It is so! It
is so!" He had warmed water simply by shaking it.

These results mean that work or energy cannot be destroyed. Though it
changes form in many ways, it is never destroyed. Neither can man create
energy; he can only direct its changes as the engineer, by the motion of
his finger in opening a valve, sets the locomotive in motion. He does
not move the locomotive. He directs the energy already in the steam.

Since the time of Galileo, men had caught now and then a glimpse of this
great law. Galileo had stated his law of machines; that, when a machine
does work, a man or a horse or some other power does an equal amount of
work upon the machine. Count Rumford had performed his experiment with
the cannon, showing that heat is produced by the work of a horse. Davy
had proved that, in the voltaic battery, something must be used up to
produce the current--the mere contact of the metals is not sufficient.
Faraday had said that in no case is there a production of electrical
power without something being used up to supply it. Mayer stated clearly
this law of energy when he said that energy cannot be created or
destroyed, but only changed from one form to another.

And yet inventors have not learned the meaning of this law. They
continue trying to invent perpetual-motion machines--machines that will
produce work from nothing. This is what a perpetual-motion machine would
be if such a machine were possible. For a machine without friction is
impossible, and friction means wasted work--work changed into heat. A
machine to keep itself running and supply the work wasted in friction
must produce work from nothing. The great law of nature is that you
cannot get something for nothing. Whether you get work, heat,
electricity, or light, something must be used up to produce it. For
whatever you get out of a machine you must give an equivalent. This law
cannot be evaded, and from it there is no appeal.




Chapter V

GREAT INVENTIONS OF THE NINETEENTH CENTURY


The discoveries of Faraday prepared the way for the great inventions of
the nineteenth century. By the middle of the century men knew how to
control the wonderful power of electricity. They did not know what
electricity is, nor do we know to-day, though we have made some progress
in that direction; but to control it and make it furnish light, heat,
and power was more important.

Before the inventions of James Watt made it possible to use steam-power,
factories were built near falling water, so that water-power could be
used. But the steam-engine made it possible to build great factories
wherever a supply of water for the boilers could be obtained. Cities
were built around the factories. Cities already great became greater.
With the growth of cities the need of a new means of producing light and
power made itself felt. Electricity promised to become the Hercules that
should perform the tasks of the modern world.

Discovery gave way to invention. During the second half of the
nineteenth century many great inventions were made and industries were
developed, while discoveries were few until near the close of the
century. Within this period the great industries which characterize our
modern civilization, and which arose out of the discoveries that science
had made in the centuries preceding, attained a high degree of
development. In this chapter we shall trace the applications of some of
the discoveries with which we have now become familiar. This will lead
us into the field of electrical invention, for we are dealing now with
the beginning of the world's electrical age.

    Electric Batteries

From the time of Volta to the time of Faraday the only means of
producing an electric current was the "voltaic battery," so called in
honor of Volta. The voltaic cell is the simplest form of electric
battery. In this cell the zinc and copper plates are placed in sulphuric
acid diluted with water. As the acid eats the zinc, hydrogen gas is
formed. This gas collects in bubbles on the copper plate and weakens the
current. The aim of inventors was to produce a steady current, to devise
a battery in which no gas would collect on the copper plate. They saw
the need of a battery that would give out a current of unchanging
strength until the zinc or the acid was used up.

The first real improvement in the battery was made by Professor Daniell,
of King's College, London. In the Daniell cell the zinc plate is in
dilute sulphuric acid, and the copper plate is in a solution of blue
vitriol or copper sulphate. Professor Daniell separated the two liquids
by placing one of them in a tube formed of the gullet of an ox. This
tube dipped into the other liquid. The hydrogen gas, as it was formed
by the acid acting on the zinc, could go through the walls of the tube,
but was stopped by the copper sulphate, and copper was deposited on the
copper plate. This copper deposit in no way interfered with the current,
so that the current was not weakened until the zinc plate or one of the
solutions was nearly consumed. A cup of porous earthenware is now used
in Daniell cells to separate the liquids (Fig. 37). By placing crystals
of blue vitriol in the battery jar, the solution of blue vitriol can be
kept up to its full strength for a very long time. The zinc in time is
consumed, and must be replaced.

[Illustration: FIG. 37--A DANIELL CELL]

In the gravity cell (Fig. 38) the same materials are used as in the
Daniell cell--copper in copper sulphate, and zinc in sulphuric acid; but
there is no porous cup. The solutions are kept separate by gravity, the
heavy copper sulphate being at the bottom. The gravity cell has until
recently been extensively used in telegraphy, and continues in use in
short-distance telegraphy and in automatic block signals. The gravity
and Daniell cells are used for closed-circuit work--that is, for work in
which the current is flowing almost constantly.

[Illustration: FIG. 38--A GRAVITY CELL]

    The Dry Battery

Another important improvement was the invention of the dry battery. You
will remember that the first battery, the one invented by Volta, was a
form of dry battery; but it was a very feeble battery compared with the
dry batteries now in use, so that we may call the dry battery a new
invention. The dry battery is falsely named. There can be no battery
without a liquid. In the dry battery the zinc cup forming the outside of
the cell is one of the plates of the cell (Fig. 39). The battery appears
to be dry because the solution of sal ammoniac is absorbed by
blotting-paper or other porous substance in contact with the zinc. The
inner plate is carbon, and this is surrounded by powdered carbon and
manganese dioxide--the latter to remove the hydrogen gas which collects
on the carbon plate. This gas weakens the current when the circuit has
been closed for a short time, but is slowly removed when the circuit is
broken. Thus the battery is said to "recover."

[Illustration: FIG. 39--SHOWING WHAT IS IN A DRY BATTERY]

The dry cell will give a strong current, but for a short time only. It
recovers, however, if allowed to rest. It can be used, therefore, only
in "open-circuit" work--such as door-bell circuits, and some forms of
fire and burglar alarm. A door-bell circuit is open nearly all the time,
the current flowing only while the button is being pressed. Some forms
of wet battery work in the same way as the dry battery, and are used
like-wise for open-circuit work. In these batteries carbon and zinc
plates in a solution of sal ammoniac are used, the same materials as in
the dry battery. The only difference is that in the dry battery the
solution is absorbed by some porous substance and the battery sealed so
that it appears to be dry.

    The Storage Battery

One of the greatest improvements in electric batteries is the storage
battery. A simple storage battery may be made by placing two strips of
lead in sulphuric acid diluted with water and connecting the lead strips
to a battery of Daniell cells or dry cells. In a short time one of the
lead strips will be found covered with a red coating. The surface of
this lead strip is no longer lead but an oxide of lead, somewhat like
the rust that forms on iron. If the lead strips are now disconnected
from the other battery and connected to an electric bell, the bell will
ring. We have here two plates, one of lead and one of oxide of lead, in
dilute sulphuric acid. This forms a storage battery.

The first storage battery was made of two sheets of lead rolled together
and kept apart by a strip of flannel. The lead strips thus separated
were immersed in dilute sulphuric acid. A current from another battery
was passed through this cell for a long time--first in one direction,
then in the other. This roughened the surface of the lead plates, so
that the battery would hold a greater charge. The battery was then
charged by passing a current through it in one direction only for a
considerable length of time. Feeble cells were used for charging. It
took days, and sometimes weeks, to charge the first storage batteries.
Then the storage battery would give out a strong current lasting for a
few hours. It slowly accumulated energy while being charged, and then
gave out this energy rapidly in the form of a strong electric current.
For this reason the storage battery was called an "accumulator."

While charging the storage cell there was formed on the negative plate a
coating of soft lead, and on the positive plate a coating of dark-brown
oxide of lead. It was found better to apply these coatings to the lead
plates before making up the battery. Later it was found that the battery
would hold a still greater charge if the plates were made in the form of
"grids" (Fig. 40), and the cavities filled with the active material--the
negative with spongy lead, and the positive with dark-brown lead oxide.
Some excellent commercial storage batteries are made from lead plates by
the action of an electric current, very much as Planté made his
batteries. Fig. 41 shows one of these plates.

[Illustration: FIG. 40--A STORAGE BATTERY, SHOWING THE "GRIDS"]

[Illustration: FIG. 41--A STORAGE-BATTERY PLATE MADE FROM A SHEET OF
LEAD]

The storage battery does not store up electricity. It produces a current
in exactly the same way as any other battery--by the action of the acid
on the plates. When this action ceases it is no longer a battery, though
it may be made one again by passing a current through it in the opposite
direction from that which it gives out. In this it differs from the
voltaic battery, for when such a battery is run down it can be restored
only by adding new solution or new plates. The storage battery is
especially useful for "sparking" in gas or gasolene motors.

Edison has invented a storage battery that will do as much work as a
lead battery of twice its weight. Edison's battery is intended
especially for use in electric automobiles. By reducing the weight of
the battery which the machine must carry the weight of the truck may
also be reduced. In the Edison battery the positive plates are made of a
grid of nickel-plated steel containing tubes filled with pure nickel.
The negative plate consists of a nickel-plated steel grid containing an
oxide of iron similar to common iron-rust.

After working a number of years on this battery and making nine thousand
experiments, Edison thought he had it perfected, and indeed it was a
great improvement over the storage batteries that had been used--much
lighter and cheaper, and more successful in operation. Two hundred and
fifty automobiles were equipped with it, and it proved superior to lead
batteries for this purpose. But it was not to Edison's liking. He threw
the machinery, worth thousands of dollars, on the scrap-heap, and worked
on for six years. He had then produced a battery as much better than the
first as the first was better than the lead battery, and he was content
to have the new battery placed on the market.

    The Dynamo

For the purpose of lighting and power the electric battery proved too
costly. Davy produced an arc light with a battery of four thousand
cells. The arc was about four inches in length and yielded a brilliant
light, but as the cost was six dollars a minute it was not thought
practical. Attempts were made early in the century to use a battery
current for power, but they failed because of the cost and the fact that
no good working motor had been invented.

Light and power were needed. Electricity could supply both. But how
overcome the difficulty of cost, and produce an electric current from
burning coal or falling water? For answer man looked to the great
discovery of Faraday and his "new electrical machine." Inventors in
Germany, France, England, Italy, and America made improvements until
from the disk dynamo of Faraday there had evolved the modern dynamo.

Electroplating and the telegraph are the only applications of the
electric current that became factors in the world's industry before the
dynamo, yet in long-distance telegraphy and in electroplating to-day the
dynamo is used. Without the dynamo, electric lighting, electric power,
and electric traction as developed in the nineteenth century would have
been impossible; in fact, the dynamo with the electric motor (which, as
we shall see, is only a dynamo reversed) is master of the field.

The way had been prepared for the application of Faraday's discovery by
William Sturgeon, an Englishman, and Joseph Henry, an American. Sturgeon
discovered that soft iron is more quickly magnetized than steel, and
found that the strength of an electromagnet can be greatly increased by
making the core of a soft-iron rod and bending the rod into the form of
a horseshoe (Fig. 42). The iron rod was coated with sealing-wax and
wound with a single layer of copper wire, the turns of wire not
touching. This was in 1825, before Faraday discovered the principle of
the dynamo.

[Illustration: FIG. 42--STURGEON'S ELECTROMAGNET]

Professor Henry still further increased the strength of the
electromagnet by covering the wire with silk, which made it possible to
wind several layers of wire on the iron core, and many times the length
of wire that had been used by Sturgeon. Fig. 43 shows such a magnet. One
of Henry's magnets weighed fifty-nine and a half pounds, and would hold
up a ton of iron. Sturgeon said: "Professor Henry has produced a
magnetic force which completely eclipses every other in the whole annals
of magnetism." With Professor Henry's invention the electromagnet was
ready for use in the dynamo. Fig. 44 shows a strong electromagnet.

[Illustration: FIG. 43--AN ELECTROMAGNET WITH MANY TURNS OF INSULATED
WIRE]

[Illustration: FIG. 44--AN ELECTROMAGNET LIFTING TWELVE TONS OF IRON]

A moving magnet causes a current to flow in a coil, but a magnet at rest
has no effect. A moving magnet is equal to a battery. In Faraday's
experiments a current was induced in a coil of wire by moving a magnet
in the coil or by making and breaking the circuit in another coil wound
on the same iron core. A current was induced in a metal disk by
revolving it between the poles of a magnet. In every case there was
motion in a magnetic field, or the field itself was changed. A changing
magnetic field is equal to a moving magnet. What is needed to induce a
current in a coil, whether it be in a dynamo, an induction-coil, or a
transformer, is a changing magnetic field about the coil or motion of
the coil in the magnetic field.

If fine iron filings are sprinkled over the poles of a magnet the
filings arrange themselves in definite lines. This is a simple
experiment which any boy can try for himself. Faraday called the lines
marked out by the iron filings "lines of force" (the lines of force of a
horseshoe magnet are shown in Fig. 36), because they indicate the
direction in which the magnet pulls a piece of iron--that is, the
direction of the magnetic force. Now, if a current is to be induced in
a wire, the wire must move across the lines of force. If the wire moves
along the lines marked out by the iron filings, there will be no
current. When a coil rotates between the poles of a magnet, the wire
moves across the lines of force and a current is induced in the coil if
the circuit is closed. This is the way a current is produced in a
dynamo.

Faraday produced a current by rotating a coil between the poles of a
steel magnet. He made a number of such machines, and used them with some
success in producing lights for lighthouses, but the defects of these
machines were so great that the lighting of a city or the development of
power on a large scale was impractical. The electromagnet was needed to
solve the problem.

    Siemens' Dynamo

The war of 1866 between Austria and Prussia and the certainty of a
coming struggle with France turned the attention of German inventors to
the use of electricity in warfare. Werner von Siemens, an artillery
officer, was improving an exploding device for mines. An electric
current was needed to produce a spark or heat a wire to redness in the
powder. Faraday had used a coil of wire turning between the poles of a
steel magnet to produce a current. In England a coil turning between the
poles of an electromagnet had been used, but the electromagnet received
its current from another machine in which a steel magnet was used.
Siemens found that the steel magnet could be dispensed with, and that a
coil turning between the poles of an electromagnet could furnish the
current for the electromagnet. Two things are needed, then, to make a
dynamo: an electromagnet and a coil to turn between the poles of that
magnet. The rotating coil, which usually contains a soft-iron core, is
called the "armature." The coil will furnish current for the magnet and
some to spare; in fact, only a small part of the current induced in the
coil is needed to keep the magnet up to its full strength, and the
greater part of the current may be used for lighting or power. The new
machine was named by its inventor "the dynamo-electric machine." The
name has since been shortened to "dynamo." The first practical problem
which the dynamo solved was the construction of an electric exploding
apparatus without the use of steel magnets or batteries. A dynamo with
Siemens' armature is shown in Fig. 45.

[Illustration: FIG. 45--A DYNAMO WITH SIEMENS' ARMATURE]

In his first enthusiasm the inventor dreamed of great things for the new
machine, among others an electric street railway in Berlin. But the
dynamo was not yet ready. The difficulty was the heating of the iron
core of the armature, caused by the action of induced currents. There
are induced currents in the iron core as well as in the coil, and, for
the same reason, the coil and the iron core within it are both moving in
a magnetic field. These little currents circling round and round in the
iron core produce heat. The rapid changing of the magnetism of the iron
also heats the iron.

It remained for Gramme, in France, to apply the proper remedy. This
remedy was an armature in which the coil was wound on an iron ring,
invented by an Italian, Pacinotti. Gramme applied the principle
discovered by Siemens to Pacinotti's ring, and produced the first
practical dynamo for strong currents. This was in 1868. A ring armature
is shown in Fig. 46. The first dynamo patented in the United States is
shown in Fig. 47. This dynamo is only a curiosity.

[Illustration: FIG. 46--RING ARMATURE]

[Illustration: FIG. 47--FIRST DYNAMO PATENTED IN THE UNITED STATES
  Intended to be used for killing whales.
  Photo by Claudy.]

    The Drum Armature

An improvement in the Siemens armature was made four years later by Von
Hefner-Alteneck, an engineer in the employ of Siemens. This improvement
consisted in winding on the iron core a number of coils similar to the
one coil of the Siemens armature, but wound in different directions.
This is called the "drum armature" (Fig. 48). The heating of the core is
prevented by building it up of a number of thin iron plates insulated
from one another and by air-spaces within the core. The insulation
prevents the small currents from flowing around in the core. The
air-spaces serve for cooling. The drum armature was a great improvement
over both the Siemens and the Gramme armatures. With the Siemens
one-coil armature there is a point in each revolution at which there is
no current. The current, therefore, varies during each revolution of the
armature from zero to full strength. In the Gramme armature only half
the wire, the part on the outside of the ring, receives the full effect
of the magnetic field. The inner half is practically useless, except to
carry the current which is generated in the outer half. Both these
difficulties are avoided in the drum armature. The dynamos of to-day are
modifications of the two kinds invented by Siemens and Gramme. Many
special forms have been designed for special kinds of work.

[Illustration: FIG. 48--A DRUM ARMATURE, SHOWING HOW AN ARMATURE OF FOUR
COILS IS WOUND]

    Edison's Compound-Wound Dynamo

Edison, in his work on the electric light and the electric railway, made
some important improvements in the dynamo. The armature of a dynamo is
usually turned by a steam-engine. Edison found that much power was
wasted in the use of belts to connect the engine and the dynamo. He
therefore connected the engine direct to the dynamo, placing the
armature of the dynamo on the shaft of the engine. He also used more
powerful field-magnets than had been used before. His greatest
improvement, however, was in making the dynamo self-regulating, so that
the dynamo will send out the strength of current that is needed. Such a
dynamo will send out more current when more lights are turned on.
Whether it supplies current for one light or a thousand, it sends out
just the current that is needed--no more, no less. It will do this if no
human being is near. An attendant is needed only to keep the machinery
well oiled and see that each part is in working order. Edison brought
about this improvement by his improved method of winding. This method is
known as "compound winding."

To understand compound winding we must first understand two other
methods of winding. In the series winding (Fig. 49), all the current
generated in the armature flows through the coils of the field-magnet.
There is only one circuit. The same current flows through the coils of
the magnet and through the outer circuit, which may contain lights or
motors. Such a dynamo is commonly used for arc lights. It will not
regulate itself. If left to itself it will give less electrical pressure
when more pressure is needed. It requires a special regulator.

[Illustration: FIG. 49--A SERIES-WOUND DYNAMO]

In the second form of winding the current is divided into two branches.
One branch goes through the coils of the field-magnet. The other branch
goes through the line wire for use in lights or motors. This is called
the "shunt winding" (Fig. 50). The shunt-wound dynamo is used for
incandescent lights. It also requires a special regulator, for if left
to itself it gives less electrical pressure when the pressure should be
kept the same.

[Illustration: FIG. 50--A SHUNT-WOUND DYNAMO]

The compound winding (Fig. 51), which was first used by Edison, is a
combination of the series and shunt windings.

[Illustration: FIG. 51--A COMPOUND-WOUND DYNAMO]

The current is divided into two branches. One branch goes only through
the field-coils. The other branch goes through additional coils which
are wound on the field-magnet, and also through the external circuit.
Such a dynamo can be made self-regulating, so that it will give always
the same electrical pressure whatever the number of lamps or motors
thrown into the circuit. In maintaining always the same pressure it of
course supplies more or less current, according to the amount of current
that is needed. This is clear if we compare the flow of electric current
with the flow of water. Open a water-faucet and notice how fast the
water flows. Then open several other faucets connected with the same
water-pipe. Probably the water will not flow so fast from the first
faucet. That is because the pressure has been lowered by the flow of
water from the other faucets. If we could make the water adjust its own
pressure and keep the pressure always the same, then the water would
always flow at the same rate through a faucet, no matter how many
other faucets were opened. This is what happens in the Edison
compound-wound dynamo. Turn on one 16-candle-power carbon lamp. It takes
about half an ampere of current. Turn on a hundred lamps connected to
the same wires, and the dynamo of its own accord keeps the pressure the
same, and supplies fifty amperes, or half an ampere for each lamp. With
this invention of Edison the dynamo was practically complete, and ready
to furnish current for any purpose for which current might be needed.
Fig. 52 shows one of Edison's first dynamos. Fig. 53 shows a dynamo used
for lighting a railway coach.

[Illustration: FIG. 52--ONE OF EDISON'S FIRST DYNAMOS
  Permission of Association of Edison Illuminating Companies.]

[Illustration: FIG. 53--A DYNAMO MOUNTED ON THE TRUCK OF A RAILWAY CAR
  The dynamo furnishes current for the electric lights in the car. When
the train is not running the current is furnished by a storage
battery.]

    Electric Power

It has been said that the nineteenth century was the age of steam, but
the twentieth will be the age of electricity. Before the end of the
nineteenth century, however, electric power had become a reality, and
there remained only development along practical lines.

We must turn to Oersted, Ampère, and Faraday to find the beginning of
electric power. In Oersted's experiment, motion of a magnet was produced
by an electric current. Ampère found that electric currents attract or
repel each other, and this because of their magnetic action. Faraday
found that one pole of a magnet will spin round a wire through which a
current is flowing. Here was motion produced by an electric current.
These great scientists discovered the principles that were applied later
by inventors in the electric motor.

A number of motors were invented in the early years of the century, but
they were of no practical use. It was not until after the invention of
the Gramme and Siemens dynamos that a practical motor was possible. It
was found that one of these dynamos would run as a motor if a current
were sent through the coils of the armature and the field-magnet; in
fact, the current from one dynamo may be made to run another similar
machine as a motor. Thus the dynamo is said to be reversible. If the
armature is turned by a steam-engine or some other power, a current is
produced. If a current is sent through the coils, the armature turns and
does work. If the machine is used to supply an electric current, it is a
dynamo. If used to do work--as, for example, to propel a street-car and
for that purpose receives a current--it is a motor. The same machine may
be used for either purpose. In practice there are some differences in
the winding of the coils of dynamos and motors, yet any dynamo can be
used as a motor and any motor can be used as a dynamo. This discovery
made it possible to transmit power to a distance with little waste as
well as to divide the power easily. The current from one large dynamo
may light streets and houses, and at the same time run a number of
motors in factories or street-cars at great distances apart. A
central-station dynamo may run the motors that propel hundreds of
street-cars. Dynamos at Niagara furnish current for motors in Buffalo
and other cities. One great scientist, who no doubt fore-saw the wonders
of electricity which we know so well to-day, said that the greatest
discovery of the nineteenth century was that the Gramme machine is
reversible.

    The First Electric Railway

The electric railway was made possible by the invention of the dynamo
and the discovery that the dynamo is reversible. At the Industrial
Exposition in Berlin in 1879 there was exhibited the first practical
electric locomotive, the invention of Doctor Siemens. The locomotive and
its passenger-coach were absurdly small. The track was circular, and
about one thousand feet in length. This diminutive railway was referred
to by an American magazine as "Siemens' electrical merry-go-round." But
the electrical merry-go-round aroused great interest because of the
possibilities it represented (Fig. 54).

[Illustration: FIG. 54--FIRST ELECTRIC LOCOMOTIVE]

The current was generated by a dynamo in Machinery Hall, this dynamo
being run by a steam-engine. An exactly similar dynamo mounted on wheels
formed the locomotive. The current from the dynamo in Machinery Hall was
used to run the other as a motor and so propel the car. The rails served
to conduct the current. A third rail in the middle of the track was
connected to one pole of the dynamo and the two outer rails to the other
pole. A small trolley wheel made contact with the third rail. The rails
were not insulated, but it was found that the leakage current was very
small, even when the ground was wet.

The success of this experiment aroused great interest, not only in
Germany, but in Europe and America. America's greatest inventor, Edison,
took up the problem. Edison employed no trolley line or third rail, but
only the two rails of the track as conductors, sending the current out
through one rail and back through the other. Of course, this meant that
the wheels must be insulated, so that the current could flow from one
rail to the other only through the coils of the motor.

As in Siemens' experiment, the motor was of the same construction as the
dynamo. The rails were not insulated, and it was found that, even when
the track was wet, the loss of electric current was not more than 5 per
cent. Edison found that he could realize in his motor 70 per cent. of
the power applied to the dynamo, whereas the German inventor was able to
realize only 60 per cent. The improvement was largely due to the
improved winding. Edison was the first to use in practical work the
compound-wound dynamo, and this was done in connection with his electric
railway. Fig. 55 shows Edison's first electric locomotive.

[Illustration: FIG. 55--FIRST EDISON ELECTRIC LOCOMOTIVE]

The question of gearing was a troublesome one. The armature shaft of the
motor was at first connected by friction gearing to the axle of two
wheels of the locomotive. Later a belt and pulleys were used. An idler
pulley was used to tighten the belt. When the motor was started and the
belt quickly tightened the armature was burned out. This happened a
number of times. Then Mr. Edison brought out from the laboratory a
number of resistance-boxes, placed them on the locomotive, and connected
them in series with the armature. These resistances would permit only a
small current to flow through the motor as it was starting, and so
prevent the burning-out of the armature coils. The locomotive was
started with the resistance-boxes in circuit, and after gaining some
speed the operator would plug the various boxes out of circuit, and in
that way increase the speed. When the motor is running there is a
back-pressure, or a pressure that would cause a current to flow in the
opposite direction from that which is running the motor. Because of this
back-pressure the current which actually flows through the motor is
small, and the resistance-boxes may be safely taken out of the circuit.
Finding the resistance-boxes scattered about under the seats and on the
platform as they were a nuisance, Mr. Edison threw them aside, and used
some coils of wire wound on the motor field-magnet which could be
plugged out of the circuit in the same way as the resistance-boxes. This
device of Edison's was the origin of the controller, though in the
controller now used on street-cars not only is the resistance cut out as
the speed of the car increases, but the electrical connections of the
motor are changed in such a way as to increase its speed gradually.
Fig. 56 shows Edison's first passenger locomotive.

[Illustration: FIG. 56--EDISON'S FIRST PASSENGER LOCOMOTIVE]

The news of the little electric railway at the Industrial Exposition in
Berlin was soon noised abroad, and the German inventor received
inquiries from all parts of the world, indicating that efforts would be
made in other countries to develop practical electrical railways. The
firm of Siemens & Halske therefore determined to build a line for actual
traffic, not for profit, but that Germany might have the honor of
building the first practical electric railway. The line was built
between Berlin and Lichterfelde, a distance of about one and a half
miles. A horse-car seating twenty-six persons was pressed into service.
A motor was mounted between the axles, and a central-station dynamo
exactly like the motor was installed. As in Edison's experimental
railway, the two rails of the track were used to carry the current. This
electric line replaced an omnibus line, and was immediately used for
regular traffic, and thus the electric railway was launched upon its
remarkable career. The first electric car used for commercial service is
shown in Fig. 57.

[Illustration: FIG. 57--FIRST COMMERCIAL ELECTRIC RAILWAY
  An old horse-car converted into an electric car.]

    Electric Lighting

From the time when the night-watchman carried a lantern to the time of
brilliantly lighted streets was less than a century. It was a time when
the rapid growth of railways and commerce brought about a rapid growth
of cities, and with the growth of cities the need of illumination.
Factories must run at night to meet the world's demands. Commerce cannot
stop when the sun sets. The centres of commerce must have light.

During this time scientists were at work in their laboratories
developing means for producing a high vacuum. They were able to pump the
air out of a glass bulb until less than a millionth part of the air
remained. They little dreamed that there was any connection between the
high vacuum and the problem of lighting. Discoverers were at work
bringing to light the principles now utilized in the dynamo. In the
fulness of time these factors were brought together to produce an
efficient system of lighting.

For a time gas replaced the lantern of the night-watchman, only to yield
the greater portion of the field to its rival, electricity.

The first efforts were in the direction of the arc light. From the
earliest times the light given out by an electric spark had been
observed. It was the aim of inventors to produce a continuous spark that
should give out a brilliant light. It was thought for a time that the
electric battery would solve the problem, but the cost of the battery
current was too great. Again we are indebted to Faraday, for it was the
dynamo that made electric lighting possible.

An arc light is produced by an electric current flowing across a gap
between two sticks of carbon. The air offers very great resistance to
the flow of electric current across this gap. Now whenever an electric
current flows through something which resists its flow, heat is
produced. The high resistance of the air-gap causes such intense heat
that the tips of the carbons become white hot and give out a brilliant
light. If examined through a smoked glass a beautiful blue arc of carbon
vapor may be seen between the carbon tips. If the current flows in one
direction only, one of the carbons, the positive, becomes hotter and
brighter than the other.

In 1878 the streets of Paris were lighted with the "Jablochkoff candle,"
a form of arc light supplied with current by the Gramme machine. In the
same year the Brush system of arc lighting was given to the public. This
was the beginning of our present system of arc lighting.

The electric arc is suitable for lighting streets and for large
buildings, but cannot be used for lighting houses. The light is too
intense. One arc would furnish enough light for a number of houses if
the light could be divided so that there might be just the right amount
of light in each room. But this is impossible with the electric arc.
The Edison system of incandescent lighting was required to solve the
problem of lighting houses by electricity.

In 1880 the Edison system was brought out for commercial use. Edison's
problem was to produce a light that could be divided into a number of
small lights, and one that would require less attention than the arc
light. He tried passing a current through platinum wire enclosed in a
vacuum. This gave a fairly good light, but was not wholly satisfactory.
He sat one night thinking about the problem, unconsciously fingering a
bit of lampblack mixed with tar which he had used in his telephone. Not
thinking what he was doing, he rolled this mixture of tar and lampblack
into a thread. Then he noticed what he had done, and the thought
occurred to him: "Why not pass an electric current through this thread
of carbon?" He tried it. A faint glow was the result. He felt that he
was on the right track. A piece of cotton thread must be heated in a
furnace in an iron mold, which would prevent the thread from burning by
keeping out the air. Then all the other elements that were in the thread
would be driven out and only the carbon remain. For three days he worked
without sleep to prepare this carbon filament. At the end of two days he
succeeded in getting a perfect filament, but when he attempted to seal
it in the glass bulb it broke. He patiently worked another day, and was
rewarded by securing a good carbon filament, sealed in a glass globe. He
pumped the air out of this globe, sealed it, and sent a current through
the carbon thread. He tried a weak current at first. There was a faint
glow. He increased the current. The thread glowed more brightly. He
continued to increase the current until the slender thread of carbon,
which would crumble at a touch, was carrying a current that would melt a
wire of platinum strong enough to support a weight of several pounds.
The carbon gave a bright light. He had found a means of causing the
electric current to furnish a large number of small lights. Fig. 58 is
an excellent photograph of Edison at work in his laboratory. Fig. 59
shows some of Edison's first incandescent lamps. He next set out in
search of the best kind of carbon for the purpose. He carbonized paper
and wood of various kinds--in fact, everything he could find that would
yield a carbon filament. He tried the fibres of a Japanese fan made of
bamboo, and found that this gave a better light than anything he had
tried before. He then began the search for the best kind of bamboo. He
learned that there are about twelve hundred varieties of bamboo. He must
have a sample of every variety. He sent men into every part of the world
where bamboo grows. One man travelled thirty thousand miles and had many
encounters with wild beasts in his search for the samples of bamboo. At
last a Japanese bamboo was found that was better than any other. The
search for the carbon fibre had cost about a hundred thousand dollars.
Later it was found that a "squirted filament" could be made that worked
as well as the bamboo fibre. This was made by dissolving cotton wool in
a certain solution, and then squirting this solution through a small
hole into a small tank containing alcohol. The alcohol causes the
substance to set and harden, and thus forms a carbon thread the size of
the hole. Fig. 60 shows the first commercial electric-lighting plant,
which was installed on the steamship _Columbia_ in 1880.

[Illustration:
  Copyright, 1904, by Byron, N. Y.
FIG. 58--EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORY]

[Illustration:
  Copyright, 1904, by William J. Hammer
FIG. 59--EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870]

[Illustration: FIG. 60--FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT;
INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880]

The carbon thread in the incandescent light is heated to a white heat,
and because it is so heated it gives out light. In air such a tiny
thread of white-hot carbon would burn in a fraction of a second. The
carbon must be in a vacuum, and so the air is pumped out of the light
bulb with a special kind of air-pump invented not long before Edison
began his work on the electric light. This pump is capable of taking out
practically all the air that was in the bulb. Perhaps a millionth part
of the original air remains.

A great invention is never completed by one man. It was to be expected
that the electric light would be improved. A number of kinds of
incandescent light have been devised, using different kinds of filaments
and adapted to a variety of uses. The original Edison carbon lamp,
however, continues in use, being better adapted to certain purposes than
the newer forms.

The mercury vapor light deserves mention as a special form of arc light.
In the ordinary arc light the arc is formed of carbon vapor, and the
light is given out from the tips of the white-hot carbons. In the
mercury vapor light the light is given out from the mercury vapor which
forms the arc. This arc may be of any desired length, and yields a soft,
bluish-white light which is a near approach to daylight.

    The Telegraph

The need of some means of giving signals at a distance was early felt in
the art of war. Flag signals such as are now used by the armies and
navies of the world were introduced in the middle of the seventeenth
century by the Duke of York, admiral of the English fleet, who afterward
became James II. of England. Other methods of communicating at a
distance were devised from time to time, but the distance was only that
at which a signal could be seen or a sound heard. No means of
communicating over very long distances was possible until the magnetic
action of an electric current was discovered. When Oersted's discovery
was made known men began to think of signalling to a distance by means
of the action of an electric current on a magnetic needle. A current may
be sent over a very long wire, and it will deflect a magnetic needle at
the other end. The movements of the needle may be controlled by opening
and closing the circuit, and a system of signals or an alphabet may be
arranged. A number of needle telegraphs were invented, but they were too
slow in action. Two other great inventions were needed to prepare the
way for the telegraph. One was the electromagnet in the form developed
by Professor Henry, a horseshoe magnet with many turns of silk-covered
wire around the soft-iron core, so that a very feeble current will
produce a magnet strong enough to move an armature of soft iron. The
magnet has this strength because the current flows so many times around
the iron core. Another need was that of a battery that could be depended
on to give a constant current for a considerable length of time. This
need was met by the Daniell cell.

The electromagnet made the telegraph possible. The locomotive made it a
necessity. Without the telegraph it would be impossible to control a
railway system from a central office. A train after leaving the central
station would be like a ship at sea before the invention of the wireless
telegraph. Nothing could be known of its movements until it returned.
The need of a telegraph was keenly felt in America when the new republic
was extended to the Pacific Coast. An English statesman said, after the
United States acquired California, that this marked the end of the great
American Republic, for a people spread over such a vast area and
separated by such natural barriers could not hold together. He did not
know that the iron wire of the telegraph would bind the new nation
firmly together.

The Morse telegraph system now in use throughout the civilized world was
made possible by the work of Sturgeon and Henry. Sturgeon's
electromagnet might have been used for telegraphy through very short
distances, but Henry's magnet, with its coils of many turns of insulated
wire, was needed for long-distance signalling. In one of the rooms of
the Albany Academy, Professor Henry caused an electromagnet to sound a
bell when the current was transmitted through more than a mile of wire.
This might be called the first electromagnetic telegraph. But the
application to actual practice was made by Morse, and the man who first
makes the practical application of a principle is the true inventor.

In 1832, on board the packet-ship _Sully_, Samuel F. B. Morse, an
American artist, forty-one years of age, was returning from Europe. In
conversation a Doctor Jackson referred to the electrical experiments of
Ampère, which he had witnessed while in Europe, and, in reply to a
question, said that electricity passes instantaneously over any known
length of wire. The thought of transmitting words by means of the
electric current at once took possession of the artist's mind. After
many days and sleepless nights he showed to friends on board the
drawings and notes he had made of a recording telegraph.

In New York, in a room provided by his brothers, he gave himself up to
the working-out of his idea, sleeping little and eating the simplest
food. Receiving an appointment as professor in the University of the
City of New York, he moved to one of the buildings of that university
and continued his experiments in extreme poverty, and at times facing
starvation, as his salary depended on the tuition fees of his pupils.

A story told by one of his pupils describes his condition at the time.

"I engaged to become one of Morse's pupils. He had three others. I soon
found that the professor had little patronage. I paid my fifty dollars;
that settled one quarter's tuition. I remember, when the second was due,
my remittance from home did not come as expected, and one day the
professor came in and said, courteously:

"'Well, Strother, my boy, how are we off for money?'

"'Why, professor, I am sorry to say I have been disappointed; but I
expect a remittance next week.'

"'Next week!' he repeated, sadly; 'I shall be dead by that time.'

"'Dead, sir?'

"'Yes; dead by starvation!'

"I was distressed and astonished. I said, hurriedly: 'Would ten dollars
be of any service?'

"'Ten dollars would save my life; that is all it would do.'"

The money was paid, all the student had, and the two dined together. It
was Morse's first meal in twenty-four hours.

The Morse telegraph sounder (Fig. 61) consists of an electromagnet and a
soft-iron armature. When no current is flowing the armature is held away
from the magnet by a spring. When the circuit is closed a current flows
through the coils of the magnet and the armature is attracted, causing
a click. When the circuit is broken the spring pulls the armature away
from the magnet, causing another click. The circuit is made and broken
by means of a key at the other end of the line. In Morse's first
instrument (Fig. 62) the armature carried a pen, which was drawn across
a ribbon of paper when the armature was attracted by the magnet. If the
pen was held by the magnet for a very short time, a dot was made; if for
a longer time, a dash. The pen was soon discarded, and the message taken
by sound only. The Morse alphabet now in use was devised by a Mr. Vail,
who assisted Morse in developing the telegraph. The thought occurred to
Mr. Vail that he could get help from a printing-office in deciding the
combinations of dots and dashes that should be used for the different
letters. The letters requiring the largest spaces in the type-cases are
the ones that occur most frequently, and for these letters he used the
simplest combinations of dots and dashes.

[Illustration: FIG. 61--A TELEGRAPH SOUNDER]

[Illustration: FIG. 62--MORSE'S FIRST TELEGRAPH INSTRUMENT
  A pen was attached to the pendulum and drawn across the strip of paper
by the action of the electromagnet. The lead type shown in the lower
right-hand corner was used in making electrical contact when sending a
message. The modern instrument shown in the lower left-hand corner is
the one that sent a message around the world in 1896.
  Photo by Claudy.]

Morse repeatedly said that, if he could make his telegraph work through
ten miles, he could make it work around the world. This promise of
long-distance telegraphy he fulfilled by the use of the relay. The relay
works in the same way as the sounder. The current coming over a long
line may be too feeble to produce a click that can be easily heard, yet
strong enough to magnetize the coils of the relay and cause the armature
to close another circuit. This second circuit includes the sounder and a
battery in the same station as the sounder, which we shall call "the
local battery." The relay simply acts as a contact key, and closes the
circuit of the local battery. Thus the current from the local battery
flows through the sounder and produces a loud click. Sometimes a relay
is used to control a second very long circuit. At the farther end of the
second circuit may be a sounder or a second relay which controls a third
circuit. Any number of circuits may be thus connected by means of
relays. This is a form of repeating system used for telegraphing over
very long distances. Fig. 63 shows a circuit with relay and sounder.

[Illustration: FIG. 63--A TELEGRAPHIC CIRCUIT WITH RELAY AND SOUNDER]

In the telegraphic circuit only one connecting wire is needed. The
earth, being a good conductor of electricity, is used as part of the
circuit. It is necessary, therefore, to make a ground connection at each
end of the line, the instruments being connected between the line wire
and the earth. For long-distance telegraphy a current from a dynamo is
used instead of a battery current. Fig. 64 shows a simple telegraphic
circuit.

[Illustration: FIG. 64--A SIMPLE TELEGRAPHIC CIRCUIT
  Two keys are shown at _K K_, and two switches at _S S_. When one key
is to be used the switch at that station must be open, and the switch at
the other station closed.]

A telegraphic message travels with the speed of light, for the speed of
electricity and the speed of light are the same. A telegraphic signal
would go more than seven times around the earth in one second if it
travelled on one continuous wire. The relays that must be used, however,
cause some delay.

In 1835 Morse's experimental telegraph was completed, and in 1837 it was
exhibited to the public, but seven years more passed before a line was
established for public use. Aid from Congress was necessary. Going to
Washington, Morse exhibited his instrument in the halls of the Capitol,
sending messages through ten miles of wire wound on a reel. The
invention was ridiculed, but the inventor did not despair. A bill for an
appropriation to establish a telegraphic line between Washington and
Baltimore passed the House by a small majority. The last day of the
session came. Ten o'clock at night, two hours before adjournment, and
the Senate had not acted. A senator advised Morse to go home and think
no more of it, saying that the Senate was not in sympathy with his
project. He went to his hotel, counted his money, and found that he
could pay his bill, buy his ticket home, and have thirty-seven cents
left. All through his work he had firmly believed that a Higher Power
was directing his work, and bringing to the world, through his
invention, a new and uplifting force; and so when all seemed lost he did
not lose heart.

In the morning a friend, Miss Ellsworth, called and offered her
congratulations that the bill had been passed by the Senate and thirty
thousand dollars appropriated for the telegraph. Being the first to
bring the news of his success, Mr. Morse promised her that the first
message over the new line should be hers. In about a year the line was
completed, and Miss Ellsworth dictated the now famous message: "What
hath God wrought!"

Soon afterward the Democratic Convention, in session in Baltimore,
received a telegraphic message from Senator Silas Wright, in Washington,
declining the nomination for the Vice-Presidency, which had been
tendered him. The convention refused to accept a message sent by
telegraph, and sent a committee to Washington to investigate. The
message was confirmed, and Morse and his telegraph became famous. Fig.
65 shows the first telegraph instrument used for commercial work.

[Illustration: FIG. 65--FIRST TELEGRAPH INSTRUMENT USED FOR COMMERCIAL
WORK
  Photo by Claudy.]

The desire to telegraph across the ocean came with the introduction of
the telegraph on land. Bare wires in the air with glass insulators at
the poles are used for land telegraphy, but bare wires in the water
could not be used, for ocean water will conduct electricity. Something
was needed to cover the wire, protect it from the water, and prevent the
escape of the electric current. Just when it was needed such a
substance was discovered. In 1843, when Morse was working on his
telegraph, it was found that the juice of a certain kind of tree growing
in the Malayan Archipelago formed a substance somewhat like rubber but
more durable, and especially suited to the insulation of wires in water.
This substance is gutta-percha. Ocean cables are made of a number of
copper wires, each wire covered with gutta-percha, the wires twisted
together and protected with tarred rope yarn and an outer layer of
galvanized iron wires. The earth is used for the return circuit, as in
the land telegraph.

    Duplex Telegraphy

The telegraph was a success, but many improvements were yet to be made.
Economy of construction was the thing sought for. To make one wire do
the work of two was accomplished by the invention of the duplex system.
In duplex telegraphy two messages may be sent in opposite directions
over the same wire at the same time. Let us take a look at some of the
methods by which this is accomplished.

One method with a long name but very simple in its working is the
differential system (Fig. 66). In the differential system the current
from the home battery divides into two branches passing around the coils
of the electromagnet in opposite directions. Now if these two branches
are so arranged that the currents flowing through them are equal, the
relay will not be magnetized, because one current would tend to make the
end A a north pole, and the other current would tend to make the same
end a south pole. The result is that the relay coil is not magnetized,
and does not attract the armature. But the current from the distant
battery comes over one of these branches only, and will magnetize the
relay. Hence, with a similar arrangement at the second station, two
messages may be sent at the same time in opposite directions.

[Illustration: FIG. 66--HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE
SAME TIME]

Another method not quite so simple in principle is the bridge method.
When the key at station _A_ (see Fig. 67) is closed, the current from
the battery at station _A_ divides at _C_, and if the resistances _1_
and _2_ are equal, and the resistance _3_ is equal to the resistance of
the line, no current will flow through the sounder. But if a current
comes over the line from the distant station this current divides at
_D_, and a part goes through the sounder, causing it to click. The
sounder is not affected, therefore, by the current from the home
battery, but is affected by the current from the distant battery.
Therefore, a message may be sent and another received at the same time.
If there is a similar arrangement at the other station, two messages may
travel over the line in opposite directions at the same time.

[Illustration: FIG. 67--HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE
SAME TIME. BRIDGE METHOD]

The differential method is used in land telegraphy, the bridge method
almost exclusively in submarine telegraphy. The next step was a
quadruplex system, by means of which four messages may be transmitted
over one wire at the same time. The first quadruplex system was invented
by Edison in 1874, and in four years it saved more than half a million
dollars. Other systems have been invented which make it possible to send
even a larger number of messages at one time over a single wire.

    The Telephone

The idea of "talking by telegraph" began to grow in the minds of
inventors soon after the Morse instrument came into use. The sound of
the voice causes vibrations in the air. (This is simply shown in the
string telephone. This telephone is made by stretching a thin membrane,
such as thin sheepskin, or gold-beaters' skin, over a round frame of
wood or metal. Two such instruments are connected by a string, the end
of the string being fastened to the middle of the stretched membrane.
The sound of the voice causes this membrane to vibrate. As the membrane
moves rapidly back and forth, it pulls and releases the string, and so
causes the membrane at the other end to vibrate and give out the sound.
This is the actual carrying of the sound vibrations along the string.)
In the telephone it is not sound vibrations but an electric current that
travels over the line wire. The telephone message, therefore, travels
with the speed of electricity, not with the speed of sound. If it
travelled with the speed of sound in air, a message spoken in Chicago
would be heard in New York one hour later; but we know that a message
spoken in Chicago may be heard in New York the instant it is spoken.

The telephone, like the telegraph, depends on the electromagnet. The
thought of inventors at first was to make the vibrations of a thin
membrane, caused by the sound of the voice, open and close a telegraphic
circuit. An electromagnet at the other end of the line would cause a
thin membrane with a piece of soft iron attached to it to vibrate, just
as the magnet in the telegraph receiver pulls and releases the
soft-iron armature as the circuit is made and broken. The thin membrane
caused to vibrate in this way would give out the sound. A telephone on
this principle was invented by Philip Reis, a schoolmaster in Germany.
The transmitter was carved out of wood in the shape of a human ear, the
thin membrane being in the position of the ear-drum. Musical sounds and
even words were transmitted by this telephone, but it could never have
been successful as a practical working telephone. The membrane in the
receiver would vibrate with the same speed as the membrane in the
transmitter, but sound depends on something more than speed of
vibration.

The Bell telephone, as known to-day, began with a study of the human
ear. Alexander Graham Bell was a teacher of the deaf. His aim was to
teach the deaf to use spoken language, and for this purpose he wished to
learn the nature of the vibrations caused by the voice. His plan was to
cause the ear itself to trace on smoked glass the waves produced by the
different letters of the alphabet, and to use these tracings in teaching
the deaf. Accordingly, a human ear was mounted on a suitable support,
the stirrup-bone removed, leaving two bones attached, and a stylus of
wheat straw attached to one of the bones. The ear-drum, caused to
vibrate by the sound, moved the two small bones and the pointer of
straw, so that when he sang or talked to the ear delicate tracings were
made on the glass.

This experiment suggested to Mr. Bell that a membrane heavier than the
ear-drum would move a heavier weight. If the ear-drum, no thicker than
tissue-paper, could move the bones of the ear, a heavier membrane might
vibrate a piece of iron in front of an electromagnet. He was at the
same time devising a telegraph for transmitting messages by means of
musical sounds. In this telegraph he was using an electromagnet in the
transmitter and another electromagnet in the receiver. He attached the
soft-iron armature of each electromagnet to a stretched membrane of
gold-beaters' skin, expecting that the sound of his voice would cause
the membrane of the transmitter to vibrate, and that, by means of the
electromagnets, the membrane of the receiver would be made to vibrate in
the same way (Fig. 68). At first he was disappointed, but after making
some changes in the armatures a distinct sound was heard in the
receiver. Later the membrane was discarded, and a thin iron disk used
with better effect.

[Illustration: FIG. 68--FIRST BELL TELEPHONE RECEIVER AND TRANSMITTER
  The receiver is on the left in the picture. A thin membrane of
gold-beaters' skin tightly stretched and fastened with a cord can be
seen on the end of the transmitter and of the receiver. An electromagnet
is also shown over each membrane. This thin membrane, with a piece of
soft iron attached, was used in place of the soft-iron disk of the
modern receiver.]

The story of Bell's struggles might seem like the repetition of the life
story of many another great inventor. He knew that he had discovered
something of great value to the world. He devoted his time to the
perfecting of the telephone, neglecting his professional work and
finally giving it up, that he might give his whole time to his
invention. He was forced to endure poverty and ridicule. He was called
"a crank who says he can talk through a wire." Men said his invention
could never be made practical. Even after he succeeded in finding a few
purchasers and some of the telephones were in actual use, people were
slow to adopt it. The idea of talking at a piece of iron and hearing
another piece of iron talk seemed like a kind of witchcraft.

In the telephone we see another use of the electromagnet. A very thin
iron disk near the poles of an electromagnet forms the telephone
receiver (Fig. 69). An electric current travels over the telephone wire.
If the current grows stronger, the magnet is made stronger and pulls
the disk toward it. If the current grows weaker, the magnet becomes
weaker and does not pull so hard on the disk. The disk then springs back
from the magnet. If these changes take place rapidly the disk moves back
and forth rapidly and gives out a sound. The sound of the voice at the
other end of the line sets the disk in the mouthpiece vibrating. The
vibrations of this disk cause the changes in the electric current
flowing over the line-wire, and the changes in the electric current
cause the disk of the receiver to vibrate in exactly the same way as the
disk at the mouthpiece. Thus the words spoken into the mouthpiece may be
heard at the receiver.

[Illustration: FIG. 69--A TELEPHONE RECEIVER]

The transmitter used by Bell was like the receiver. Two receivers from
the common telephone connected by two wires may be used as a telephone
without batteries. Fig. 70 shows a complete telephone made of two
receivers connected by two wires. The disk in one receiver which is now
used as a transmitter is made to vibrate by the sound of the voice. Now
when a piece of iron moves back and forth in a magnetic field it
strengthens and weakens the field. So the magnetic field in the
transmitter is rapidly changed by the movement of the iron disk. Now we
have found that whenever a coil of wire is in a changing magnetic field
a current is induced in the coil. The small coil in the transmitter,
therefore, has a current induced in it. We have also found that when the
magnetic field is made stronger the induced current flows in one
direction, and when the field is made weaker the current flows in the
opposite direction. Since the field in the transmitter is made
alternately stronger and weaker, the current in the coil flows first in
one direction, then in the opposite direction--that is, we have an
alternating current. This alternating current, of course, flows over the
line-wire and through the coil in the receiver. In the receiver the
alternating current will alternately strengthen and weaken the magnetic
field, and as it does so the pull of the magnet on the iron disk is
strengthened and weakened. The iron disk in the receiver, therefore,
vibrates in exactly the same way as the disk in the transmitter, and so
gives out a sound just like that which is acting on the transmitter.

[Illustration: FIG. 70--TWO RECEIVERS USED AS A COMPLETE TELEPHONE]

In the Blake transmitter, which is now commonly used, the disk moves a
pencil of carbon which presses against another pencil of carbon. This
varies the pressure between the two pencils of carbon. A battery current
flows through the two carbons, and as the pressure of the carbons
changes the strength of the current changes. When the carbons are
pressed together more closely the current is stronger. When the pressure
is less the current is weaker. We have, then, a varying current through
the carbons. This current flows through the primary coil of an
induction-coil, the secondary being connected to the line-wire. Now a
current of varying strength in the primary induces an alternating
current in the secondary. We have, then, an alternating current flowing
over the line-wire. This alternating current acts on the magnetic field
of the receiver in the way described before, causing the disk in the
receiver to vibrate and give out the sound.

For long-distance work a carbon-dust transmitter (Fig. 71) is used. In
this there are many granules of carbon, so that instead of two
carbon-points in contact there are many. This makes the transmitter more
sensitive.

[Illustration: FIG. 71--CARBON-DUST TRANSMITTER]

The strength of current required for the telephone is very small. To
transmit a telephone message requires less than a hundred-millionth part
of the current required for a telegraphic message. The work done in
lifting the telephone receiver a distance of one foot, if changed into
an alternating current, would be sufficient to keep up a sound in the
receiver for a hundred thousand years. Because of its extreme
sensitiveness the telephone requires a complete wire circuit. The earth
cannot be used for the return circuit, as in the case of the telegraph.
Disturbances in the earth, vibration, leakage currents from trolley
lines, and so forth, would interfere seriously with the action of the
telephone.

When the telephone was invented it was commonly remarked that it could
not take the place of the telegraph in commerce, for the latter gave the
merchant some evidence of a business transaction, while the telephone
left no sign. There was a time when men feared to trust each other, but
now large business deals are made by telephone; products of the farm,
the factory, and the mine are bought and sold in immense quantities
without a written contract or even the written evidence of a telegram.
Thus the telephone has developed a spirit of business honor.

    The Phonograph

The phonograph grew out of the telephone. It is said to be the only one
of Edison's inventions that came by accident, yet only a man of genius
would have seen the meaning of such an accident. He was singing into the
mouthpiece of a telephone when the vibrations of the disk caused a fine
steel point to pierce one of his fingers held just behind the disk. This
set him to thinking. If the sound of his voice could cause the disk to
vibrate with force enough to pierce the skin, would it not make
impressions on tin-foil, and so make a record of the voice that could be
reproduced by passing the point rapidly over the same impressions? He
gave his assistants the necessary instructions, and soon the first
phonograph was made.

This disk in the phonograph is set in vibration by sound vibrations in
the air in the same way as the disk in the telephone transmitter.
Attached to the disk is a needle-point which, of course, vibrates with
the disk. If a cylinder with a soft surface is turned rapidly under the
steel point as it vibrates, impressions are made in the cylinder
corresponding to the movements of the disk. The cylinder must move
forward as it turns, so that its path will be a spiral. If, now, the
stylus is placed at the starting-point and the cylinder turned rapidly
the stylus will move rapidly up and down as it goes over the
indentations in the cylinder, and so cause the metal disk to vibrate and
give out a sound like that received at first. In the earliest
phonographs the cylinder was covered with tin-foil. Later the so-called
"wax records" came into use. These cylinders are not made of wax, but of
very hard soap. Fig. 72 shows an instrument in which the sound of the
voice caused a pencil-point to trace a wavy line on a cylinder. This
instrument may be called a forerunner of the phonograph. Fig. 73 shows
Edison's first phonograph with a modern instrument placed beside it for
comparison.

[Illustration: FIG. 72--THE PHONAUTOGRAPH, A FORERUNNER OF THE
PHONOGRAPH]

[Illustration: FIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENT
  Photo by Claudy.]

    Gas-Engines

Cannons are the oldest gas-engines. Indeed, the principle of the cannon
is the same as that of the modern gas-engine, the piston in the engine
taking the place of the cannon-ball. The power in each case is obtained
by explosion--in the cannon the explosion of powder, in the engine the
explosion of a mixture of air and gas. Powder-engines with pistons were
proposed in the seventeenth century, and some were actually built, but
it proved too difficult to control them, and the idea of the gas-engine
was abandoned for more than a hundred years.

The discovery of coal-gas near the close of the eighteenth century gave
a new impetus to the gas-engine. John Barber, an Englishman, built the
first actual gas-engine. He used gas distilled from wood, coal, or oil.
The gas, mixed with the proper proportion of air, was introduced into a
tank which he called the exploder. The mixture was fired and issued out
in a continuous stream of flame against the vanes of a paddle-wheel,
driving them round with great force.

In 1804 Lebon, a French engineer, was assassinated, and the progress of
the gas-engine set back a number of years, for this engineer had
proposed to compress the mixture of gas and air before firing, and to
fire the mixture by an electric spark. This is the method used in
gas-engines to-day.

The first practical working gas-engine was invented by Lenoir, a
Frenchman, in 1860. From this time to the end of the century the
gas-engine developed rapidly, receiving a new impulse from the
increasing demand for the motor-car.

The engine of the German inventors, Otto and Langen, brought out in
1876, marked the beginning of a new era. The greater number of engines
used in automobiles to-day are of the kind known as the Otto cycle, or
four-cycle, engine. This engine is called four-cycle because the piston
makes four strokes for every explosion. There is one stroke to admit the
mixture of gas and air to the cylinder, another to compress the gas and
air, at the beginning of the third stroke the explosion takes place, and
in the fourth stroke the burned-out gases are driven out of the
cylinder. The working of the four-cycle gas-engine is made clear in
Figs. 74, 75, 76, and 77.

[Illustration: FIG. 74--FIRST STROKE. GAS AND AIR ADMITTED TO THE
CYLINDER]

[Illustration: FIG. 75--SECOND STROKE. MIXTURE OF GAS AND AIR
COMPRESSED]

[Illustration: FIG. 76--THIRD STROKE. THE MIXTURE IS EXPLODED AND
EXPANDS, DRIVING THE PISTON FORWARD]

[Illustration: FIG. 77--FOURTH STROKE, EXHAUST. THE BURNED-OUT MIXTURE
OF GAS AND AIR EXPELLED FROM THE CYLINDER]

    THE FOUR-CYCLE GAS-ENGINE

In such a gas-engine the power is applied to the piston only in one
stroke out of every four, while in the steam-engine the power is applied
at every stroke. It would seem, therefore, that a steam-engine would do
more work than a gas-engine for the same amount of heat, but such is not
the case; in fact, a good gas-engine will do about twice as much work as
a good steam-engine for the same amount of fuel. The reason is that the
steam-engine wastes its heat. Heat is given to the condenser, to the
iron of the boiler, to the connecting pipes and the air around them,
while in the gas-engine the heat is produced in the cylinder by the
explosion and the power applied directly to the piston-head. More than
this, a steam-engine when at rest wastes heat; there must be a fire
under the boiler if the engine is to be ready for use on short notice.
When a gas-engine is at rest there is no fire, nothing is being used up,
and yet the engine can be started very quickly. A gas-engine can be made
much lighter than a steam-engine of the same horse-power. The automobile
and the flying-machine require very light engines. Without the
gas-engine the automobile would have remained imperfect and crude, while
the flying-machine would have been impossible.

In a two-cycle gas-engine there is an explosion for every two strokes of
the piston, or one explosion for every revolution of the crank-shaft.
During one stroke the mixture of gas and air on one side of the piston
is compressed and a new mixture enters on the opposite side of the
piston. At the end of this stroke the compressed mixture is exploded,
and power is applied to the piston during about one-fourth of the next
stroke. During the remainder of the second stroke the burned-out gas
escapes, and the fresh mixture passes over from one side of the piston
to the other ready for compression. The two-cycle engine is simpler in
construction than the four-cycle, having no valves. It also has less
weight per horse-power. The cylinder of a two-cycle engine is shown in
Fig. 78.

[Illustration: FIG. 78--TWO-CYCLE GAS-ENGINE. CRANK AND CONNECTING-ROD
ARE ENCLOSED WITH THE PISTON]

A steam-engine is self-starting. The engineer has only to turn the steam
into the cylinder, but the gas-engine requires to be turned until at
least one explosion takes place, for until there is an explosion of gas
and air in the cylinder there is no power.

A gas-engine may have a number of cylinders. Four-cylinder and
six-cylinder engines are common. In a four-cylinder, four-cycle engine,
while one cylinder is on the power stroke the next is on the compression
stroke, the third on the admission stroke, and the fourth on the exhaust
stroke. Fig. 79 shows the Selden "explosion buggy" propelled by a
gas-engine. This machine was the forerunner of the modern automobile.

[Illustration: FIG. 79--SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE
MODERN AUTOMOBILE]

    The Steam Locomotive

Late in the eighteenth century a mischievous boy put some water in a
gun-barrel, rammed down a tight wad, and placed the barrel in the fire
of a blacksmith's forge. The wad was thrown out with a loud report, and
the boy's play-mate, Oliver Evans, thought he had discovered a new
power. The prank with the gun-barrel set young Evans thinking about the
power of steam. It was not long until he read a description of a
Newcomen engine. In the Newcomen engine, you will remember, it was the
pressure of air, not the pressure of steam, that lifted the weight.
Evans soon set about building an engine in which the pressure of steam
should do the work. He is sometimes called the "Watt of America," for he
did in America much the same work that Watt did in Scotland. Evans built
the first successful non-condensing engine--that is, an engine in which
the steam, after driving the piston, escapes into the air instead of
into a condenser. The non-condensing engine made the locomotive
possible, for a locomotive could not conveniently carry a condenser.
Evans made a locomotive which travelled very slowly. He said, however:
"The time will come when people will travel in stages moved by
steam-engines from one city to another, almost as fast as birds can fly,
fifteen or twenty miles an hour."

The inventor who made the first successful locomotive was George
Stephenson, and it is worth noting that one of his engines, the
"Rocket," possessed all the elements of the modern locomotive. He
combined in the "Rocket" the tubular boiler, the forced draft, and
direct connection of the piston-rod to the crank-pin of the
driving-wheel.

The "Rocket" was used on the first steam railway (the Stockton &
Darlington, in England), which was opened in 1825. There had been other
railways for hauling coal by means of horses over iron tracks, and other
locomotives that travelled over an ordinary road; but this was the first
road on which a steam-engine pulled a load over an iron track, the
first real railroad. Fig. 80 shows the "Rocket" and two other early
locomotives.

[Illustration: FIG. 80--SOME EARLY LOCOMOTIVES
  The one on the right is Stephenson's "Rocket."
  Photo by Claudy.]

In order to build a railroad between Liverpool and Manchester for
carrying both passengers and freight it was necessary to secure an act
of Parliament. Stephenson was compelled to undergo a severe
cross-examination by a committee of Parliament, who feared there would
be great danger if the speed of the trains were as high as twelve miles
an hour. He was asked:

"Have you seen a railroad that would stand a speed of twelve miles an
hour?"

"Yes."

"Where?"

"Any railroad that would bear going four miles an hour. I mean to say
that if it would bear the weight at four miles an hour it would bear it
at twelve."

"Do you mean to say that it would not require a stronger railway to
carry the same weight at twelve miles an hour?"

"I will give an answer to that. I dare say every person has been over
ice when skating, or seen persons go over, and they know that it would
bear them better at a greater velocity than it would if they went
slower; when they go quickly the weight, in a measure, ceases."

"Would not that imply that the road must be perfect?"

"It would, and I mean to make it perfect."

For seven miles the road must be built over a peat bog into which a
stone would sink to unknown depths. To convince the committee, however,
and secure the act of Parliament was more difficult than to build the
road. But Stephenson was one of the men who do things because they
never give up, and the road was built.

    How a Locomotive Works

To understand how a locomotive works, let us consider how the steam is
produced, how it acts on the piston, and how it is controlled. The steam
is produced in a locomotive in exactly the same way that steam is
produced in a tea-kettle. Now everybody knows that a quart of water in a
tea-kettle with a wide bottom placed on a stove will boil more quickly
than the same amount of water in a tea-pot with a narrow bottom. The
greater the heating-surface--that is, the greater the surface of heated
metal in contact with the water--the more quickly the water will boil
and the more quickly steam can be produced. In a locomotive the aim is
to use as large a heating-surface as possible. This is done by making
the fire-box double and allowing the water to circulate in the space
between the inner and outer parts, except underneath; also by placing
tubes in the boiler through which the heated gases and smoke from the
fire must pass. An ordinary locomotive contains two hundred or more of
these tubes. The water surrounds these tubes, and is therefore in
contact with a very large surface of heated metal. In some engines the
water is in the tubes, and the heated gases surround the tubes.

The steam as it enters the cylinder should be dry--that is, it should
not contain drops of water. This is accomplished by allowing the steam
from the boiler to pass into a dome above the boiler. Here the steam,
which is nearly dry, enters a steam-pipe leading to the cylinder (Fig.
81). The steam is admitted to the cylinder by means of a slide-valve.
From the diagram it can easily be seen that the valve admits steam first
on one side of the piston, then on the other. It can also be seen that
the valve closes the admission-port, and so cuts off the steam before
the piston has made a full stroke. The steam that is shut up in the
cylinder continues to expand and act on the piston. At the same time the
valve opens the exhaust-port, allowing the steam to escape from the
other side of the piston; but it closes this port before the piston has
quite finished the stroke. The small quantity of steam thus shut up acts
like a cushion to prevent the piston striking the end of the cylinder
with too great force. The exhaust-steam escapes through a blast-pipe
into the chimney, drives the air before it up the chimney, and thus
makes a greater draft of air through the fire-box. This is called the
forced draft. The escape of the exhaust-steam causes the puffing of the
locomotive just after starting. After the engine is under way the
engineer partly shuts off the steam by means of the reversing lever and
the puffing is less noticeable.

[Illustration: FIG. 81--HOW A LOCOMOTIVE WORKS
  The arrows show the course of the steam.]

The action of the steam may be summed up as follows:

1. Steam admitted to the cylinder (admission).

2. Valve closes admission-port (cut-off).

3. Steam shut up in the cylinder expands, acting on the piston
(expansion period).

4. Valve opens exhaust-port to allow used steam to escape (exhaust).

The devices for controlling the steam are the throttle-valve and the
valve-gear. The throttle-valve is at the entrance to the steam-pipe in
the steam-dome. This valve is opened and closed by means of a rod in the
engineer's cab.

Stephenson's link-motion valve-gear is used on most locomotives. The
forward rod in the diagram is in position to act upon the valve-rod
through the lever _L_. Suppose the reversing-lever is drawn back to the
dotted line; then the forward rod will be raised and the backward rod
will come into position to act on the lever _L_. If this is done while
the locomotive is at rest the valve is moved through one-half a complete
stroke. In the diagram the steam enters the cylinder on the right of the
piston. After this movement of the valve the steam would enter on the
left side of the piston. In the present position the locomotive would
move forward, but if the valve is changed so as to admit steam to the
left of the piston while the connecting-rod is in the position shown
then the engine will move backward. Thus the direction can be controlled
by the engineer in the cab. Of course, this can be done while the engine
is in motion. The forward rod and the backward rod are each moved by an
eccentric on the axle of the front driving-wheel. The two eccentrics are
in opposite positions on the axle. An eccentric acts just like a crank,
causing the rod to move forward and backward as the axle turns, and of
course this motion is given to the valve-rod through the lever. When the
link is set midway between the forward and the backward rod the valve
cannot move. When the link is raised or lowered part way the valve makes
a short stroke, and less steam is admitted to the cylinder than with a
full stroke. In starting the locomotive the valve is set to make a full
stroke. When the train is under headway the valve is set for a short
stroke to economize steam. The valve-gear and the throttle-valve
together take the place of the governor in the stationary engine, but
while the governor acts automatically these are controlled by the
engineer.

In reality a locomotive is two engines, one on either side, connected to
the same driving-wheels. But the two piston-rods are connected to the
driving-wheels at points which are at right angles with each other, so
that when the crank on one side is at the end of a stroke--the "dead
centre"--that on the other side is on the quarter, either above or below
the axle, ready for applying the greatest turning force.

The expansion-engine was designed to use more of the power of the steam
than can be done in the single-cylinder engine. In the double
expansion-engine the steam expands from one cylinder into another. The
second cylinder must be larger in diameter than the first. In the triple
expansion-engine the steam expands from the second cylinder into a
third, still larger. The second and third cylinders use a large part of
the power that would be wasted with only one cylinder.

    The Turbine

One of the great inventions relating to steam-power is the
steam-turbine. The water-turbine is equally useful in relation to
water-power. The water-turbine and the steam-turbine work in very much
the same way, the difference being due to the fact that steam expands as
it drives the engine, while water drives it by its weight in falling, or
by its motion as it rushes in a swift stream or jet against the blades
of the turbine.

The first steam-engine, that of Hero in the time of Archimedes, was a
form of turbine (Fig. 82). It was driven by the reaction of the steam as
it escaped into the air. The common lawn-sprinkler, that whirls as the
water rushes through it, is a water-turbine that works in the same way.
"Barker's Mill" is the name applied to a water-turbine that works like
the lawn-sprinkler. As the water rushes out of the opening it pushes
against the air. It cannot push against the air without pushing back at
the same time. Never yet has any person or object in nature been able to
push in one direction only. It cannot be done. If you push a cart
forward you push backward against the ground at the same time. If there
were nothing for you to push back against your forward push would not
move the cart a hair's-breadth. If you doubt this, try to push a cart
when you are standing on ice so slippery that you cannot get a foothold.
It is the backward push of the water in the lawn-sprinkler and the
backward push of the steam in Hero's engine that cause the machine to
turn.

[Illustration: FIG. 82--HERO'S ENGINE]

The turbines in common use for both water and steam power have curved
blades. The reason for curving the blades can best be seen by referring
to an early form of water-wheel. The best water-turbine is only an
improved form of water-wheel. The first water-wheels had flat blades,
and these answered very well so long as only a low power was needed and
it was not necessary to save the power of the water. It was found,
however, that there was a great waste of power in the wheel with flat
blades. One inventor proposed to improve the wheel by curving the blades
in such a way that the water would glide up the curve and then drop
directly downward (Fig. 83). The water then gives up practically all of
its power to the wheel and falls from the wheel. It would have no power
to move a second wheel. In this way he used practically all the power
of the water. To save the power of the water by making all of the water
strike the wheel at high speed the channel was made narrow just above
the wheel, forming a mill-race. This applies to the undershot wheel. In
the overshot wheel (Fig. 84) the power depends on the weight of the
water and on its height. The water runs into buckets attached to the
wheel, and, as it falls in these buckets, turns the wheel. The undershot
wheel and the mill-race represent a common form of turbine, that form
in which the steam or the water is forced in a jet against a set of
curved blades. Fig. 85 shows a steam-turbine run by a jet of steam. In
the water-turbine there are two sets of blades. One set rotates, the
other remains fixed. The use of the fixed blades is to turn the water
and drive it in the right direction against the moving blades. In some
forms of turbine there are more than two sets of blades. The steam, as
it passes through, gives up some of its power to each set of blades
until, after passing the last set, it has given up nearly all its power.
The action of the steam in this turbine is somewhat like that in the
expansion-engine, in which the steam gives up a portion of its power in
each cylinder. Fig. 86 is from a photograph of a modern steam-turbine,
and Fig. 87 is a drawing of the same turbine showing the course of the
steam. Fig. 88 is a turbine that runs a large dynamo.

[Illustration: FIG. 83--AN UNDERSHOT WATER-WHEEL WITH CURVED BLADES]

[Illustration: FIG. 84--AN OVERSHOT WATER-WHEEL]

[Illustration: FIG. 85--DE LAVAL STEAM-TURBINE
  Driven by a jet of steam striking the blades.]

[Illustration: FIG. 86--A MODERN STEAM-TURBINE WITH TOP CASING RAISED
SHOWING BLADES]

[Illustration: FIG. 87--DIAGRAM OF TURBINE SHOWN IN FIG. 86
  The arrows show the course of the steam.]


[Illustration: FIG. 88--A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING
14,000 ELECTRICAL HORSE-POWER
  The steam enters through the large pipe at the left.]

In 1897, as the battle-ships of the British fleet were assembled to
celebrate the Diamond jubilee of Queen Victoria, a little vessel a
hundred feet long darted in and out among the giant ships, defied the
patrol-boats whose duty it was to keep out intruders, and raced down the
lines of battle-ships at the then unheard-of speed of thirty-five knots
an hour. It was the _Turbinia_, fitted with the Parsons turbine. This
event marked the beginning of the modern turbine. It also marked the
beginning of a revolution in steam propulsion.

The Parsons turbine does not use the jet method, but the steam enters
near the centre of the wheel and flows toward the rim, passing over a
number of rows of curved blades. The Parsons turbine is used on the
fastest ocean liners. The _Lusitania_, one of the fastest steamships in
the first decade of the twentieth century, has two sets of high and low
pressure turbines with a total of 68,000 horse-power.

The windmill is a form of turbine driven by the air. As the air rushes
against the blades of the windmill, it forces them to turn. If the
windmill were turned by some mechanical power, it would drive the air
back, and we should have a blower. This is what we have in the electric
fan, a small windmill driven by an electric motor so that it drives the
air instead of being driven by it. The blades of the windmill and the
electric fan are shaped very much like the screw propeller. The screw
propeller, driven by an engine, would drive the water back if the ship
were firmly anchored, just as the fan drives the air. But it cannot
drive the water back without pushing forward on the ship at the same
time, and this forward push propels the ship. It is difficult to attain
what is now regarded as high speed with a single screw. With engines in
pairs and two lines of shafting higher power can be used. The best
steamers, therefore, are fitted with the twin-screw propeller. Some
large steamers have three and some four screws.

The screw propellers of turbine steamships are made of small diameter,
that they may rotate at high speed without undue waste of power. By the
use of turbine engines and twin-screw propellers, the weight of the
machinery has been greatly reduced. The old paddle-wheels, with
low-pressure engines, developed only about two horse-power for each ton
of machinery. The turbine, with the twin-screw propeller, develops from
six to seven horse-power for every ton of machinery. The modern steamer,
with all its machinery and coal for an Atlantic voyage, weighs no more
than the engines of the old paddle-wheel type and coal would weigh for
the same horse-power. The steam-turbine and the twin-screw propeller
have made rapid ocean travel possible.




Chapter VI

THE TWENTIETH-CENTURY OUTLOOK


We have seen that the latter half of the nineteenth century was a time
of invention. It was a time when the great discoveries of many centuries
bore fruit in great inventions. It was thought by some scientists that
all the great discoveries had been made, and that all that remained was
careful work in applying the great principles that had been discovered.
So far was this from being true that in the last ten years of the
nineteenth century discoveries were made more startling, if possible,
than any that had preceded. The nineteenth century not only brought
forth many great inventions, but handed down to the twentieth century a
series of discoveries that point the way to still greater inventions.

    Air-Ships

For centuries men sailed over the water at the mercy of the wind. The
sailing vessel is helpless in a storm. Early in the nineteenth century
they learned to use the power of steam for ocean travel, and the wind
lost its terrors. Late in the eighteenth century men learned to sail
through the air in balloons even more at the mercy of the wind than the
sailing vessels on the ocean. More than a hundred years later they
learned to propel air-ships in the teeth of the wind. The nineteenth
century saw the mastery of the water. The twentieth is witnessing the
mastery of the air.

The first balloon ascension was made in 1783, two men being carried over
Paris by what Benjamin Franklin called a "bag of smoke." The balloon was
a bag of oiled silk open at the bottom. In the middle of the opening was
a grate in which bundles of fagots and sheaves of straw were burned. The
heated air filled the balloon, and as the heated air was lighter than
the air around it the balloon could rise and carry a load. Beneath the
grate was a wicker car for the men. They were supplied with straw and
fagots with which to feed the fire. When they wanted to rise higher they
added fuel to heat the air in the balloon. When they wished to descend
they allowed the fire to die out, so that the air in the balloon would
cool. They could not guide the balloon, but drifted with the wind. That
great philosopher Benjamin Franklin, who saw the ascension, said that
the time might come when the balloon could be made to move in a calm and
guided in a wind. In the second ascension bags of sand were taken as
ballast, and the car was suspended from a net which enclosed the
balloon. In this second ascension hydrogen gas was used in place of
heated air.

The greatest height ever reached by a human being is about seven miles.
This height was first reached in 1862 by two balloonists who nearly lost
their lives in the adventure. At a height of nearly six miles one of the
men became unconscious. The other tried to pull the valve-cord to allow
the gas to escape, but found that the cord was out of his reach. His
hands were frozen, but he climbed out of the car into the netting of the
balloon, secured the cord in his teeth, returned to the car, and threw
the weight of his body on the cord. This opened the valve and the
balloon descended.

Those who go to great heights now provide themselves with tanks of
compressed oxygen. Then when the air becomes so thin and rare that
breathing is difficult they can breathe from the oxygen tanks.

A captive balloon in war serves as an observation tower from which to
observe the enemy. It is connected to the ground by a cable. This cable
is wound on a drum carried by the balloon wagon. The balloon can be
lowered or raised by winding or unwinding the cable.

The gas-bag is sometimes made of oiled silk, sometimes of two layers of
cotton cloth with vulcanized rubber between. The cotton cloth gives the
strength needed, and the rubber makes the bag gas-tight.

The most convenient gas for filling balloons is heated air, but the air
cools rapidly and loses its lifting power. Coal-gas furnished by city
gas-plants is sometimes used. This gas will lift about thirty-five
pounds for every thousand cubic feet. A balloon holding thirty-five
thousand cubic feet of coal gas will easily lift the car and three
persons. The lightest gas is hydrogen. This gas will lift about seventy
pounds for every thousand cubic feet. Hydrogen is made by the action of
sulphuric acid and water on iron. If a bit of iron is thrown into a
mixture of sulphuric acid and water bubbles of hydrogen gas will rise
through the liquid. This gas will burn if a lighted match is brought
near.

A balloon without propelling or steering apparatus is not an air-ship.
It may be raised by throwing out ballast or lowered by letting out gas,
but further than this the aeronaut has no control over its movements.
The balloon moves with the wind. No breeze is felt, for balloon and air
move together. To the aeronaut the balloon seems to be in a dead calm.
It is only when he catches sight of houses and trees and rivers darting
past below that he realizes that the balloon is moving.

If a balloon has a propelling apparatus it may move against the wind, or
it may outspeed the wind. A balloon with propelling and steering
apparatus is called a "dirigible" balloon, which means a balloon that
can be guided. Figs. 89 and 90 are from photographs of a "dirigible"
used in the British army. Such a balloon is usually long and pointed
like a spindle or a cigar. It is built to cut the air, just as a rowboat
built for speed is long and pointed so that it may cut the water. The
propeller acts like an electric fan. An electric fan drives the air
before it, but the air pushes back on the fan just as much as the fan
pushes forward on the air, and if the fan were suspended by a long cord
it would move backward. So the large fan or screw propeller on an
air-ship drives the air backward, and the air reacts and drives the ship
forward. In the same way the screw-propeller of an ocean liner drives
the vessel forward by the reaction of the water.

[Illustration: FIG. 89--BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR
FLIGHT]

[Illustration: FIG. 90--BASKET, MOTOR, AND PROPELLER OF THE BRITISH ARMY
AIR-SHIP "NULLI SECUNDUS"]

A balloon rises for the same reason that wood floats on water. The wood
is lighter than water, and the water holds it up. The balloon is
lighter than air and the air pushes it up. The upward push of the air is
just equal to the weight of the air that would fill the same space the
balloon fills. The balloon can support a load that makes the whole
weight of the balloon and its load together equal to the weight of the
air that would fill the same space. For the balloon to rise the load
must be somewhat lighter than this. A balloon may be made lighter than
air by filling it with heated air or coal-gas. Hydrogen, however, is
used in the better balloons and in air-ships of the "lighter than air"
type.

The air-ship must, of course, use a very light motor. A steam-engine
cannot be made light enough. Neither can an electric motor, if we add
the weight of the storage battery that would be required. Air-ships have
been propelled by both steam-engines and electric motors, but with low
speed because of the weight of the engine or motor. The only successful
motor for this purpose is the gasolene motor, which is a form of
gas-engine using gas formed by the evaporation of gasolene.

The first air-ship that could be controlled and brought back to the
starting-point was made in France, in 1885, by Captain Renard, of the
French army. It was a cigar-shaped balloon, with a screw propeller run
by an electric motor of eight horse-power. The ship attained a speed of
thirteen miles an hour.

A more successful air-ship was that built by Santos Dumont. With this
ship, in 1901, he won a prize of $20,000, which had been offered to the
builder of the first air-ship that would sail round the Eiffel Tower in
Paris from the Aerostatic Park of Vaugirard, a distance of about three
miles, and return in half an hour.

The balloon part of this air-ship was 112-1/2 feet long and 19-1/2 feet
in diameter, holding about 6400 cubic feet of gas. The car was built of
pine beams no larger in section than two fingers and weighing only 110
pounds. This car could be taken apart and put in a trunk. A gasolene
automobile motor was used, and thus it is seen that the automobile aided
in solving the problem of sailing through the air. It was the automobile
that led to the construction of light and powerful gasolene motors. The
car and motor were suspended from the balloon by means of piano wires,
which at a short distance were invisible, so that the man in the car
appeared in some mysterious way to follow the balloon. The ship was
turned to the left or right by means of a rudder. It was made to ascend
or descend by shifting the weight of a heavy rope that hung from the
car, thus inclining the ship upward or downward.

Count Zeppelin, of Germany, constructed a much larger dirigible balloon
than that of Santos Dumont. The balloon of the first Zeppelin air-ship
was 390 feet in length, with a diameter of about 39 feet. It was divided
into seventeen sections, each section being a balloon in itself. These
sections serve the same purpose as the water-tight compartments of a
battle-ship. An accident to one section would not mean the destruction
of the entire ship. Within the balloon is a framework of aluminum rods
extending from one end to the other and held in place by aluminum rings
twenty-four feet apart. The balloon contains about 108,000 cubic feet of
gas, and it costs about $2500 to fill it. One filling of gas will last
about three weeks. There are two cars, each about ten feet long, five
feet wide, and three feet deep. The cars are connected by a narrow
passageway made of aluminum wires and plates, making a walking distance
of 326 feet--longer than the decks of many ocean steamers. A sliding
weight of 300 kilograms (about 600 pounds) serves the same purpose as
the guide-ropes in the Santos Dumont air-ship. By moving this weight
forward or backward the ship is raised or lowered at the bow or stern,
and thus caused to glide up or down. Anchor-ropes are carried for use in
landing. The ship is propelled by four screws, and guided by a number
of rudders placed some in front and some in the rear. The first Zeppelin
air-ship carried four passengers. The work of Dumont and Zeppelin has
led the great powers to manufacture dirigible balloons for use in time
of war. Fig. 91 shows one of the Zeppelin air-ships sailing over a lake.

[Illustration: FIG. 91--A ZEPPELIN AIR-SHIP]

A larger air-ship, the _Deutschland_, built later by Count Zeppelin, was
the first air-ship to be used for regular passenger service. The
_Deutschland_ is shown in Fig. 92. The _Deutschland_ carried the crew
and twenty passengers. It operated for a time as a regular passenger
air-ship between Friedrichshafen and Düsseldorf, a distance of three
hundred miles. The _Deutschland_ was wrecked in a storm on June 28,
1910, but it was successfully operated long enough to give Germany the
honor of establishing the first air-ship line for regular passenger
service. This is an honor perhaps equally as great as that of
establishing the first commercial electric railway, which also belongs
to Germany. An American army air-ship is shown in Fig. 93.

[Illustration: FIG. 92--COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST
AIR-SHIP IN REGULAR PASSENGER SERVICE]

[Illustration:
  Copyright by Pictorial News Co.
FIG. 93--THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMY]

    The Aeroplane

The aeroplane is a later development than the dirigible balloon. The
aeroplane is heavier than air. So is a bird and so is a kite. What
supports a kite or a bird as it soars? Every boy knows that the strings
of a kite must be attached so that the kite is inclined and catches the
wind underneath. Then the wind lifts the kite. In still air the kite
will not fly unless the boy who holds the string runs very fast and so
causes an artificial breeze to blow against the kite. In much the same
way a hovering bird is held aloft by the wind. In a dead calm the bird
must flap its wings to keep afloat. If the kite string is cut the kite
tips over and drops to the earth because it has lost its balance. The
lifting power of the wind is well shown in the man-lifting kites which
are used in the British army service. In a high wind a large kite is
used in place of a captive balloon. It is a box-kite made of bamboo and
carries a passenger in a car, the car running on the cable which
attaches the kite to the ground. Now suppose a kite with a motor and
propeller in place of a string and a boy to run with it, and that the
kite is able to balance itself, then it will sail against a wind of its
own making and you have a flying-machine heavier than air.

The first aeroplane that would fly under perfect control of the operator
was built by the Wright brothers at Dayton, Ohio. When they were boys,
Bishop Wright gave his two sons, Orville and Wilbur, a toy flyer. From
that time on the thought of flying through the air was in their minds. A
few years later the death of Lilienthal, who was killed by a fall with
his glider in Germany, stirred them, and they took up the problem in
earnest. They read all the writings of Lilienthal and became acquainted
with Mr. Octave Chanute, an engineer of Chicago who had made a
successful glider. They soon built a glider of their own, and
experimented with it each summer on the huge sand-dunes of the North
Carolina coast.

A glider is an aeroplane without a propeller. With it one can cast off
into the air from a great height and sail slowly to the ground. Before
attempting to use a motor and propeller, the Wrights learned to control
the glider perfectly. They had to learn how to prevent its being tipped
over by the wind, and how to steer it in any direction. This took years
of patient work. But the problem was conquered at last, and they
attached a motor and propeller to the glider, and had an air-ship under
perfect control and with the speed of an express-train. Their flyer of
1905, which made a flight of twenty-four miles at a speed of more than
thirty-eight miles an hour, carried a twenty-five-horse-power gasolene
motor, and weighed, with its load, 925 pounds. Figs. 94 and 95 show the
Wright air-ship in flight. Fig. 97 shows the mechanism.

[Illustration: FIG. 94--IN FULL FLIGHT]

[Illustration:
  Copyright, 1908, by Pictorial News Co.
FIG. 95--WRIGHT AIR-SHIP IN FLIGHT
  Rear view, showing propellers.]

[Illustration: FIG. 97--THE SEAT AND MOTOR OF THE WRIGHT AEROPLANE
  Photo by Pictorial News Co.]

    How the Wright Aeroplane Is Kept Afloat

The Wright aeroplane is balanced by a warping or twisting of the planes
1 and 2, which form the supporting surfaces (Fig. 96). If left to itself
the machine would tip over like a kite when the string is cut and drop
edgewise to the ground. Suppose the side _R_ starts to fall. The corners
_a_ and _e_ are raised by the operator while _b_ and _f_ are lowered,
thus twisting the planes, as shown in the dotted lines of the figure.
The side _R_ then catches more wind than the side _L_. The wind exerts a
greater lifting force on _R_ than on _L_, and the balance is restored.
The twist is then taken out of the machine by the operator. A ship when
sailing on an even keel presents true unwarped planes to the wind.

[Illustration: FIG. 96--HOW THE WRIGHT AIR-SHIP IS KEPT AFLOAT
  This picture represents a glider. The motor-driven aeroplane is balanced
by the warping of the planes in the same way as the glider.]

The twisting is brought about by a pull on the rope 3, which is attached
at _d_ and _c_, and passes through pulleys at _g_ and _h_. When the rope
is pulled toward the left the right end is tightened and slack is paid
out at the left end. This pulls down the corner _d_, and raises _e_. The
corner _a_ is raised by the post which connects _a_ and _e_. The rope 4,
passing from _a_ to _b_ through pulleys at _m_ and _n_, is thus drawn
toward _a_ and pulls down the corner _b_. Thus _a_ is raised and _b_ is
lowered. At the same time rope 4 turns the rear rudder to the left, as
shown by the dotted lines, thus forcing the side _R_ against the wind.
Of course, if the left side of the machine starts to fall, the rope 3 is
pulled toward the right, and all the movements take place in the
opposite direction. The ropes are connected to a lever, by which the
operator controls the warping of the planes. These movements are
possible because the joints are all universal, permitting movement in
any direction. In whatever position the planes may be set, they are held
perfectly rigid by the two ropes, together with others not shown in the
figure. The machine is guided up or down by the front horizontal rudder.

When the aeroplane swings round a curve the outer wing is raised because
it moves faster than the inner wing, and therefore has greater lifting
force. Thus the aeroplane banks its own curves.

The Wright flying-machine is called a biplane because it has two
principal planes, one above the other. A number of successful
flying-machines have been built with only one plane, and these are
called monoplanes. A monoplane that early became famous is that of
Blériot (Fig. 98). The Blériot monoplane was the first flying-machine to
cross the English Channel. This machine is controlled by a single lever
mounted with a ball-and-socket coupling, so that it can move in any
direction. When on the ground it is supported by three wheels like
bicycle wheels, so that it does not require a track for starting, but
can start anywhere from level ground. The Wright and the Blériot
represent the two leading types of early successful flying-machines.

[Illustration:
  Copyright by M. Brauger, Paris
FIG. 98--THE BLÉRIOT MONOPLANE]

    Submarines

Successful navigation beneath the surface of the water, though not
carried to the extent imagined by Jules Verne, was a reality at the
beginning of the twentieth century. Instead of twenty thousand leagues
under the sea, less than a hundred leagues had been accomplished, but no
one can foretell what the future may have in store.

The principal use of the submarine is in war. It is a diving
torpedo-boat, and acts under cover of water, as the light artillery on
land is secured behind intrenchments. The weapon used by the submarine
is the torpedo. The torpedo is itself a small submarine able to propel
itself, and if started in the water toward a certain object, to go under
water straight to the mark. It carries a heavy charge either of
guncotton or dynamite, which explodes when the torpedo strikes a solid
object, such as a battle-ship. The first torpedo was intended to be
steered from the shore by means of long tiller-ropes, and to be
propelled by a steam-engine or by clockwork. The Whitehead fish torpedo,
invented in 1866, is self-steering. At the head of the torpedo is a
pointed steel firing-pin. When the torpedo strikes a ship or any rigid
object this steel pin is driven against a detonator cap which is in the
centre of the charge of dynamite. The blow causes the cap to explode,
and the explosion of the cap explodes the dynamite. The torpedo is so
arranged that it cannot explode until it is about thirty yards away from
the ship from which it is fired. The steel pin cannot strike the cap
until a small "collar" has been revolved off by a propeller fan, and
this requires a distance of about thirty yards. The screw propeller is
driven by compressed air. A valve which is worked by the pressure of the
water keeps the torpedo at any depth for which the valve is set. The
torpedo contains many ingenious devices for bringing it quickly to the
required depth and keeping it straight in its course. One of these
devices is the gyroscope, which will be described under the head of
"spinning tops." Whitehead torpedoes are capable of running at a speed
of over thirty-seven miles an hour for a range of two thousand yards and
hitting the mark aimed at almost as accurately as a gun. The submarine
boat carries a number of torpedoes, and has one torpedo-tube near the
forward end from which to fire the torpedoes.

It would be very difficult for one submarine to fight another submarine,
for the submarine when completely submerged is blind. It could not see
in the water to find its enemy. The torpedo-boat-destroyer is able to
destroy a submarine by means of torpedoes, shells full of high
explosives, or quick-firing guns. Advantage must be taken of the moment
when the submarine comes to the surface to get a view of her enemy.

One of the great enemies of the submarine will probably be the air-ship,
for while the submarine when under water cannot be seen from a ship on
the surface, it can, under favorable conditions, be seen from a certain
height in the air.

Most submarines use a gasolene motor for surface travel, and an electric
motor run by a storage battery for navigation below the surface. The
best submarines can travel at the surface like an ordinary boat, or
"awash"--that is, just below the surface--with only the conning tower
projecting above the water, or they can travel completely submerged.

The rising and sinking of the submarine depend on the principle of
Archimedes. The upward push of the water is just equal to the weight of
the water displaced. If the water displaced weighs more than the boat,
then the upward push of the water is greater than the weight of the boat
and the boat rises. However, the boat can be made to dive when its
weight is just a little less than the weight of the water displaced.
This is done by means of horizontal rudders which may be inclined so as
to cause the boat to glide downward as its propeller drives it forward.

The magnetic compass is not reliable in a submarine with a hull made of
steel. The electric motor used for propelling the boat under water also
interferes with the action of the compass, because of its magnetic
field. The gyroscope, which we shall describe later, is not affected by
magnetic action, and may take the place of the compass.

Water ballast is used, and when the submarine wishes to dive, water is
admitted into the tanks until the boat is nearly heavy enough to sink of
its own weight. It is then guided downward by the horizontal rudder. The
submarine is driven by a screw propeller, and some submarines are
lowered by means of a vertical screw. Just as a horizontal screw propels
a vessel forward, so a vertical screw will propel it downward. When the
submarine wishes to rise, it may do so by the action of its rudder, or
the water may be pumped out of its tanks, when the water will raise it
rapidly. A submarine which is kept always a little lighter than water
will rise to the surface in case of accident to its machinery. Figs. 99,
100, and 101 are from photographs of United States submarines.

[Illustration: FIG. 99--THE "PLUNGER"
  Photo by Pictorial News Co.]

[Illustration: FIG. 100--U. S. SUBMARINE "SHARK" READY FOR A DIVE
  Photo by Pictorial News Co.]

[Illustration: FIG. 101--FIRST SUBMARINE CONSTRUCTED IN UNITED STATES.
IT WENT TO THE BOTTOM WITH SEVEN MEN, WHO WERE DROWNED
  Photo by Pictorial News Co.]

There is one kind of submarine built for peaceful pursuits which
deserves mention. It is the _Argonaut_, invented by Simon Lake. This
remarkable boat crawls along the bottom of the sea, but not at a very
great depth. It is equipped with divers' appliances, and is used in
saving wreckage. Divers can go out through the bottom of the boat, walk
about on the sea bottom, and when through with their work re-enter the
boat; all the while boat and men are, perhaps, a hundred feet below the
surface. The divers' compartment, from which the divers go out into the
water, is separated by an air-tight partition from the rest of the boat.
Compressed air is forced into this compartment until the pressure of the
air equals the pressure of the water outside. Then the door in the
bottom is opened, and the air keeps the water out. The men in their
diving-suits can then go out and in as they please.

For every boat there is a depth beyond which it must not go. The penalty
for going beyond this depth is a battered-in vessel, for the pressure
increases with the depth. Every time the depth is increased thirty-two
feet the pressure is increased fifteen pounds on every square inch.
Beyond a certain depth the vessel cannot resist the pressure. Submarines
have been made strong enough to withstand the pressure at a depth of
five thousand feet, or nearly a mile. Most submarines, however, cannot
go deeper than a hundred and fifty feet.

Air is supplied to the occupants of the boat either from reservoirs
containing compressed air or oxygen, or by means of chemicals which
absorb the carbon dioxide produced in breathing and restore the needed
quantity of oxygen to the air.

While the men in the boat cannot see in the water, they can see objects
on the surface of the water, even when their boat is several feet below
the surface, by means of the periscope. This is an arrangement of lenses
and mirrors in a tube bent in two right angles, which projects a short
distance above the surface and can be turned in any direction (Fig.
102). Thus the boat, while itself nearly invisible, can have a clear
view of the battle-ship which it is about to attack.

[Illustration: FIG. 102--HOW MEN IN A SUBMARINE SEE WHEN UNDER THE
WATER]

    Some Spinning Tops that Are Useful

Every one knows that a top will stand upright only when it is spinning.
Most tops when spinning will stand very rough treatment without being
upset. The whip-top will stand a severe lashing. Spin a top upright and
give it a knock. It will go round in a circle in a slanting position,
and after a time will right itself. If the top is struck toward the
south it will not bow toward the south but toward the east or west. In
throwing a quoit, the quoit must be given a spinning motion or the
thrower cannot be certain how it will alight. A coin thrown up with a
spinning motion will not turn over. The quoit and the coin are like the
top. They will not turn over easily when spinning. For the same reason a
rifle bullet is set spinning by the spiral grooves in the bore of the
gun, and it goes straight to its mark. With a smooth-bore gun that does
not set the bullet spinning the gunner cannot be sure of his aim.

It took a long time to discover that the spinning top is a useful
machine. It is useful because of its steady motion, because it is
difficult to turn over. It was discovered by Newton long ago that every
moving object tries to keep on in the direction in which it is moving. A
moving object always requires some force to change its direction. The
spinning top is a beautiful illustration of this principle. The top that
is most useful is the gyroscope top (Fig. 103). It is mounted on pivots
so arranged that the top can turn in any direction within the frame that
supports it. If the top is set spinning one may turn the frame in any
direction, but the top does not change direction. The axis of the top
will point in the same direction all the while the top is spinning, no
matter how the supporting frame is moved about. The top will spin on a
string. If attached inside a box the box can be made to stand on one
corner while the top is spinning.

[Illustration: FIG. 103--A TOP THAT SPINS ON A STRING]

This top, which is so hard to upset, has been used in ships to prevent
the ship being rolled by the waves. A large fly-wheel is mounted in the
middle of the vessel on a horizontal axle. A fly-wheel is only a large
top. It spins with a steady motion, and because of its larger size it is
very much harder to overturn than a toy top. The fly-wheel in the ship
resists the rolling force of the waves and steadies the ship, so that
even with high waves the rolling can scarcely be felt. The waves do not
so readily break over the ship when thus steadied by the revolving
wheel.

The gyroscope is also used in some forms of torpedo to give the torpedo
steady motion. By means of a spring released by a trigger the gyroscope
within the torpedo is set spinning before the torpedo enters the water.
The gyroscope keeps its direction unchanged, and as the torpedo turns
one way or the other the gyroscope acts upon one or the other of two
valves connected with the compressed-air chambers from which the screws
of the torpedo are driven. The air thus set free by the gyroscope drives
a piston-rod connected with a rudder in such a way as to right the
torpedo. The torpedo goes through the water with a slightly zigzag
motion, but never more than two feet out of the line in which it was
aimed.

    The Monorail-Car

Another use of the gyroscope is in the monorail-car. To make a car run
on a single rail, with its weight above the rail, was impossible until
the use of the gyroscope was discovered. In the monorail-car invented by
Brennan (Fig. 104) there are two gyroscopes, each weighing fifteen
hundred pounds, driven at a speed of three thousand revolutions a minute
by an electric motor. Each gyroscope wheel with its motor is mounted in
an air-tight casing from which the air is pumped out. The wheel will run
much more easily in a vacuum than in air, for the air offers very great
resistance to its motion. The wheels are placed one on each side of the
car with their axles horizontal. When the car starts to fall the
spinning gyroscopes right it much as a spinning top rights itself if
tipped to one side by a blow. If the wind tips the car to the left the
gyroscopes incline to the right until the car is again upright. If the
load is heavier on the right side the car inclines itself toward the
left just as a man leans to the left when carrying a load on his right
shoulder. In rounding a curve the car leans to the inside of the curve
just as a bicycle rider does, and as a railway train is made to do by
laying the outer rail of the curve higher than the inner rail. Two
gyroscopes spinning in opposite directions are necessary to keep the car
from falling when rounding a curve.

[Illustration: FIG. 104--A CAR THAT RUNS ON ONE RAIL
  Louis Brennan's full-size monorail.]

The gyroscope may be used in place of a compass. If it is set spinning
in a north and south direction it will continue to spin in a north and
south direction, no matter how the ship may turn. It is even more
reliable than the compass, for it is not affected by magnetic action.
Possibly some of the great inventions yet to be made will be new uses of
the spinning top.

    Liquid Air and the Greatest Cold

For a long time after men had learned the use of the furnace and could
produce great heat, the greatest cold known was that of the
mountain-top. Men wondered what would happen if air could be made colder
than the frost of winter, but knew not how to bring about such a result.
They wondered what things could be frozen that remain liquid or gaseous
even in the cold of winter.

The first artificial cold was produced by a mixture of salt and ice,
such as we now use in an ice-cream freezer. In time men learned other
ways of producing great cold and even to manufacture ice in large
quantities.

The cold of liquid air is far greater than that of ice or even a
freezing mixture of salt and ice. Liquid air is simply air that is so
cold that it becomes a liquid just as steam when cooled forms water.
Steam has only to be cooled to the temperature of boiling water, while
air must be cooled to 314 degrees below zero on the Fahrenheit scale.

If it were possible for us to live in such a climate, and the world were
cooled to the temperature of liquid air, we should have a curious world.
Watch-springs might be made out of pewter, bells of tin, and piano wires
of solder, for these metals are made stronger by the extreme cold of
liquid air. There would be no air to breathe. Oceans and rivers would be
frozen solid, and the air would form a liquid ocean about thirty-five
feet deep. This ocean of liquid air would be kept boiling a long time by
the heat of the ice beneath it, for ice is hot compared with liquid air.
The ice would cool as it gave up its heat to the liquid air and in time
become as cold as the liquid air itself.

Liquid air has been shipped thousands of miles in a double walled tin
can, the space between the two walls being filled with felt. The felt
protects the liquid air from the heat of the air without. The liquid air
evaporates slowly, and escapes through a small opening at the top.

Professor Dewar, a successor of Faraday in the Royal Institution,
invented the Dewar bulb, by means of which the evaporation of the liquid
air is prevented. This bulb is a double-walled flask. In the space
between the two walls of the flask is a vacuum. Now a vacuum is the best
possible protection against heat. If we were to take a bottle full of
air and pump out from the bottle all except about a thousandth of a
millionth of the air it contained at first we should have such a vacuum
as that of the Dewar bulb. With such a vacuum around it ice could be
kept from melting for many days even in the hottest weather, for no heat
can go through a vacuum.

But the greatest cold is not the cold of liquid air. Liquid hydrogen is
so cold that it freezes air. When a flask of liquid hydrogen is opened
there is a small snow-storm of frozen air in the mouth of the flask. But
even this is not the greatest cold. The liquid hydrogen may be frozen,
forming a hydrogen snow whose temperature is 435 degrees below zero.
This is nearly equal to the cold of the space beyond the earth's
atmosphere, which is the greatest possible cold.

    The Electric Furnace and the Greatest Heat

The greatest heat that has yet been produced artificially is that of the
electric arc. The exact temperature of the electric arc is not known
with certainty. It is known, however, that the temperature of the
hottest part of the arc is not less than 6500 degrees Fahrenheit. When
we compare this with the temperature of the hottest coal furnace, which
is about 4000 degrees, we can very easily understand that something is
likely to happen at the temperature of the electric arc that could not
happen in an ordinary furnace.

If an electric arc is enclosed by something that will hold the heat in
we have an electric furnace, and any substance placed in the furnace may
be made nearly as hot as the arc itself. In the electric furnace any
substance, whether found in nature or prepared artificially, may be
melted or vaporized.

It was Henri Moissan, Professor of Chemistry at the Sorbonne in Paris,
who made the first great discoveries in the use of the electric furnace
and produced the first artificial diamonds. The study of diamonds led
Moissan to believe that in nature they are formed by the cooling of a
melted mixture of iron and carbon. He could prepare such a mixture with
his electric furnace, he thought, and so make diamonds like those of the
diamond mines. So, with an electric furnace having electrodes as large
as a man's wrist, a mixture of iron and charcoal in a carbon crucible,
and a glass tank filled with water, Moissan set out to change the
charcoal to diamonds. At a temperature of more than six thousand degrees
the iron and charcoal were melted together. For a time of from three to
six minutes the mixture was in the intense heat. Then the covering of
the furnace was removed and the crucible with the melted mixture dropped
into the tank of water. With some fear this was done for the first time,
for it was not known what would happen when such a hot object was
dropped into cold water. But no explosion occurred, only a violent
boiling of the water, a fierce blazing of the molten mass, and then a
gradual change of color from white to red and red to black. With boiling
acids and other chemicals the refuse was removed, and the fragments that
remained were found to be diamonds, small, it is true, so small that
they could be seen only with the aid of a microscope, but giving promise
of greater things to come. The outer crust of iron held the melted
charcoal under enormous pressure while it slowly cooled and formed the
diamond crystals. The process of manufacturing diamonds is illustrated
in Figs. 105, 106, and 107.

[Illustration: FIG. 105--MANUFACTURING DIAMONDS--FIRST OPERATION
  Preparing the furnace. Charcoal and iron ore placed in a crucible and
subjected to enormous heat electrically.]

[Illustration: FIG. 106--MANUFACTURING DIAMONDS--SECOND OPERATION
  The furnace at work.]

[Illustration: FIG. 107--MANUFACTURING DIAMONDS--THIRD OPERATION
  Plunging the crucible into cold water. Observe the white-hot carbon
just removed from the furnace.]

The electric furnace has made possible the preparation of substances
unknown before, and the production in large quantities at low cost of
substances that before were too costly for general use. One of the best
known of these substances is aluminum. With the discovery of the
electric-furnace method of extracting aluminum from its ores, the price
of aluminum fell from one hundred and twenty-four dollars per pound to
twelve cents per pound.

Among the many uses of the electric furnace we may mention the
preparation of calcium carbide, which is used in producing the acetylene
light; carborundum, a substance almost as hard as diamond; and
phosphorus, which is used in making the phosphorus match. It is used
also to some extent in the manufacture of glass, and, in some cases, for
extracting iron from its ores.

    The Wireless Telegraph

A ship in a fog is struck by another ship. The water rushes in, puts out
the fires in the boilers, the engines stop, the ship is helpless in
mid-ocean in the darkness of the night. But the snapping of an electric
spark is heard in one of the cabins. Soon another vessel steams
alongside. The life-boats are lowered and every person is saved. The
call for help had gone out over the sea in every direction for two
hundred miles. Another ship had caught the signal and hastened to the
rescue, and the world realized that the wireless telegraph had robbed
the sea of its terrors.

Without the curious combination of magnets, wires, and batteries on the
first ship no signal could have been sent, and without such a
combination on the second ship the signal would have passed unheeded.
How was this combination discovered, and how does it work?

Faraday, as we have seen, discovered the principle of the
induction-coil. With the induction-coil a powerful electric spark can be
produced. The friction electrical machine was known long before the time
of Faraday. Franklin proved that a stroke of lightning is like a spark
from an electrical machine, only more powerful. These great discoverers
did not know, however, that an electric spark sends out something like
light which travels in all directions. They did not know it, because
they had no eyes to see this strange light.

I will tell you a fable to make the meaning clear. There once lived a
race of blind men. Not one of them could see. They built houses and
cities, railroads and steamships, but they did everything by touch and
sound. When they met they touched each other and spoke, and each man
knew his friend by the sound of his voice. One day a wise man among them
said he believed there was something besides the sound of the voice with
which they could make signals to each other. Another wise man thought
upon this matter for some time and brought forth a proof that there is
something called light, though no man could see it. Another, wiser and
more practical, invented an eye which any man could carry about with him
and see the light when he turned it in the direction from which the
light was coming. Thereafter each man carried a light that flashed like
the flashing of a firefly. Each man also carried an eye, and each could
see his friend as well as hear the sound of his voice.

The fable is true. The light which no man had seen we now call electric
waves. The eye with which any one can perceive this light is the
receiving instrument of the wireless telegraph. The strange light
flashed out whenever an electric spark passed from an electrical
machine, a Leyden jar, an induction-coil, or as lightning in the clouds,
but for hundreds of years this light was unseen. The human eye could not
see it, and no artificial eye that would catch electric waves had been
invented. A man in England, James Clerk-Maxwell, first proved that there
is such a light. Heinrich Hertz, a German, first made an eye that would
catch the waves from the electric spark, and the man who first perfected
an eye with which one could catch the electric waves at a great distance
and improved the instruments for sending out such waves was Marconi.

The fable is true, for electric waves are like the light from the sun.
They go through space in all directions as light does. They will not
merely go through air, but through what we call empty space, or a
vacuum, as light will. If we think of waves somewhat like water waves,
but not exactly like them, rushing through space, we have about as good
a picture of electric waves as we can well form in our minds. As the
light of a lamp goes out in all directions, so do the electric waves go
out in all directions from the place where the electric spark passes.
Since these waves go through what we call empty space, we must think of
something in that space and that it is not really empty. Examine an
incandescent electric lamp. The bulb was full of air when the carbon
thread was placed in it. The air was then pumped out until only about a
millionth part remained. The bulb was then sealed at the tip and made
air-tight. We say the space inside is a vacuum. If the bulb is broken
there is a loud report as the air rushes in. Is the bulb really empty
after the air is pumped out? Is anything left in the bulb around the
carbon thread? Turn on the electric current and the carbon thread
becomes white hot. The light from the white-hot carbon thread goes out
through the vacuum. There is nothing in the vacuum that we can see or
feel or handle, but something must be there to carry the light from the
carbon thread. The light of the sun comes to the earth through
ninety-three million miles of space. Is there anything between the earth
and the sun through which this light can pass? Light, we know, is made
up of waves, and we cannot think of waves going through empty space.
There must be something between the sun and the earth. That something
through which the light of the sun comes to the earth we call the ether.
It is the ether that carries the light across the vacuum in the light
bulb as well as from the sun to the earth. Electric waves used in
wireless telegraphy go through this same ether. The light of the sun is
made up of the same kind of waves, and we do not think it strange
because it is so common. It is true we do not see light waves, but they
affect our eyes so that by means of them we can see objects and perceive
the flashing of a light. So with the wireless receiving instrument we
do not see the electric waves, but we perceive the flashing of the
strange light. Electric waves and light travel with the same
speed--186,000 miles in a second. A wireless message will go around the
earth in about one-seventh of a second.

Electric waves will go through a brick wall as readily as sunlight will
go through a glass window, but that is not so strange as it may seem.
Red light will not go through blue glass. Blue glass holds back the red
light, but lets the blue light go through. So the brick wall holds back
common light, but allows the light which we call electric waves to go
through.

Some waves on water are longer than others. So electric waves are longer
than light waves. That is the only difference between them. In fact, the
light of the sun is made up of very short electric waves. These short
waves affect our eyes, but the longer electric waves do not. We are
daily receiving the wireless-telegraph waves from the sun, which we call
light. Electric waves used in wireless telegraphy vary from about six
hundred feet to two miles in length, while the longest light waves that
affect our eyes are only one thirty-three-thousandth of an inch in
length.

The sensitive part of the Marconi receiving apparatus is the coherer.
The first coherer was made in 1890 by Prof. Edward Branly, of the
Catholic University of Paris. Very fine metal filings were enclosed in a
tube of ebonite and connected in a circuit with a battery and a
galvanometer. The filings have so high a resistance that no current
flows. The waves from an electric spark, however, affect the filings so
that they allow the current to flow. The electric waves are said to
cause the filings to cohere--that is, to cling together more closely. It
is a peculiar form of electric welding. Branly discovered that a slight
tapping of the tube loosens the filings and stops the flow of the
current.

All that was needed for wireless telegraphy was at hand. Men knew how to
produce electric waves of any desired length. They knew how they would
act. A sensitive receiver had been discovered. There was needed the
practical man who should combine the parts, improve details, and apply
the wireless telegraph to actual use. This was the work of Guglielmo
Marconi. In 1894, at the age of twenty, Marconi began his experiments on
his father's estate, the Villa Grifone, Bologna, Italy. Fig. 108 is from
a photograph of Marconi and his wireless sending and receiving
instruments.

[Illustration: FIG. 108--MARCONI AND HIS WIRELESS-TELEGRAPH SENDING AND
RECEIVING INSTRUMENTS]

To Marconi, telegraphing through space without wires appears no more
wonderful than telegraphing with wires. In the wire telegraph electric
waves, which we then call an electric current, follow a wire somewhat as
the sound of the voice goes through a speaking-tube. In the wireless
telegraph the electric waves go out through space without any wire to
guide them. The light and heat waves of the sun travel to us through
millions of miles of space without requiring any conducting wire. That
electric waves should go though space in the same way that light does is
no more wonderful than that the waves should follow all the turns of a
wire.

The sending instrument used by Marconi includes an induction-coil, one
side of the spark-gap being connected to the earth and the other to a
vertical wire (Fig. 109). There must be a battery of Leyden jars in the
circuit of the secondary coil. The induction-coil may be operated by a
storage battery or dynamo. The vertical wire, or antenna, is to the
sending instrument what the sounding-board is to a violin. It is needed
to increase the strength of the waves. In the wireless telegraph some
wires must be used. It is called wireless because the stations are not
connected by wires. The antenna for long-distance work consists of a
network of overhead wires. When the key is pressed a rapid succession of
sparks passes across the spark-gap. The antenna, or overhead wire, is
thus made to send out electric waves. By pressing the key for a longer
or shorter time, a longer or shorter series of waves may be produced and
a correspondingly longer or shorter effect on the receiver. In this
manner the dots and dashes of the Morse alphabet may be transmitted.

[Illustration: FIG. 109--DIAGRAM OF WIRELESS-TELEGRAPH SENDING
APPARATUS]

At the receiving station there are two circuits. One includes a coherer,
a local battery, and a telegraph relay (Fig. 110). The other circuit,
which is opened and closed by the relay, includes a recording instrument
and a tapper. One end of the coherer is connected to the earth and the
other to a vertical wire like that used for the transmitter. The
electric waves weld the filings in the coherer, and this closes the
first circuit. The relay then closes the second circuit, the recording
instrument records a dot or a dash, and the tapper strikes the coherer
and breaks the filings apart ready for another stream of electric waves.

[Illustration: FIG. 110--DIAGRAM OF MARCONI WIRELESS-TELEGRAPH RECEIVING
APPARATUS
  The second circuit described in the text is not shown here. The relay
and the second circuit would take the place of the electric bell. In the
circuit as shown here the electric waves would cause the coherer to
close the circuit and ring the bell.]

With this arrangement it was possible to work only two stations at one
time. Though stations were to be established in all the cities of Great
Britain, only one message could be sent at one time, and all stations
but one must keep silence, because a second series of waves would mingle
with the first and confusion would result.

Marconi's next effort was to make it possible to send any number of
messages at one time. This led to his system of tuning the sending and
receiving instruments. With this system the receiving instrument will
take a message only from a sending instrument with which it is in tune.
It is possible, therefore, for any number of wireless-telegraph stations
to operate at the same time, the waves crossing one another in all
directions without interfering, each receiver responding to the waves
intended for it. An ocean steamer can, with the tuned system, send one
message and receive another from a different station at the same time.

Marconi's ambition was to send a wireless message across the Atlantic.
Quietly he made his preparation, building at Poldhu, Cornwall, England,
a more powerful transmitter than had yet been used. At noon on the 12th
of December, 1901, he sat in a room of the old barracks on Signal Hill,
near St. Johns, Newfoundland, waiting for a signal from England. His
assistants at the Poldhu station were to telegraph across the ocean the
letter "S" at certain times each day. On the table was the receiving
apparatus, made very sensitive, and including a telephone receiver. A
wire led out of the window to a huge kite, which the furious wind held
four hundred feet above him. One kite and a balloon used for supporting
the antenna had been carried out to sea. He held the telephone receiver
to his ear for some time. The critical time had come for which he had
worked for years, for which his three hundred patents had prepared the
way, and for which his company had erected the costly power station at
Poldhu. Calmly he listened, his face showing no sign of emotion.
Suddenly there sounded the sharp click of the tapper as it struck the
coherer. After a short time Marconi handed the telephone receiver to his
assistant. "See if you can hear anything," he said. A moment later,
faintly and yet distinctly, came the three little clicks, the dots of
the letter "S" tapped out an instant before in England. Marconi's
victory was won.

A flying-machine can be equipped with a wireless-telegraph outfit, so
that a man can telegraph while flying through the air. Two men are
needed, one to operate the flying-machine, the other to send the
telegraphic messages. This has been done with the Wright machine and
with some dirigible balloons. Of course, the wireless instruments on the
flying-machine cannot be connected to the ground. Instead of the ground
connection there is a second antenna.--one antenna on each side of the
spark-gap. While in the ordinary wireless instruments the discharge
surges back and forth between the antenna and the earth, in the
flying-machine wireless the discharge surges back and forth between the
two antennæ. In the Wright machine, when equipped for wireless
telegraphy, the two antennæ are placed one under the upper plane, the
other under the lower plane of the flying-machine.

More power is required for the wireless than for the wire telegraph. In
the wire telegraph about one-hundredth horse-power is required to send a
message one hundred and twenty miles. To send a message the same
distance with the wireless requires about ten horse-power, or a thousand
times as much as with the wire telegraph. This is because in the
wireless telegraph the waves go out in all directions, and much of the
power is wasted. In the wire telegraph the electric waves are directed
along the wire and very little of the power is wasted. For the same
reason a person's voice can be heard a long distance through a
speaking-tube. The speaking-tube guides the sound and prevents it from
scattering somewhat as the wire guides the electric waves.

The overhead wires of a wireless-telegraph station send out a "dark"
light while a message is being sent. (See frontispiece.) Standing near
the station on a dark night one can see nothing, but can hear only the
terrific snapping of the electric discharge. The camera, however, shows
that light goes out from the wires. It is light of shorter waves than
any that the eye can perceive, but the sensitive film of the
photographic plate makes it known to us.

    The Wireless Telephone

In sending a message by the wire telegraph the current flows over the
line wire when the key is pressed. When the key is released the current
stops. The circuit is made and broken for every dot or dash. This we may
call an interrupted current. Now we have seen that the attempt to invent
a wire telephone using an interrupted current failed. While one is
talking over the wire telephone a current (alternating) must be flowing
over the line wire. The sound of the voice does not make and break the
circuit, but changes the strength of the current. This alternating
current is wonderfully sensitive. It can vary in the rate at which it
alternates or the number of alternations per second to correspond to
sound of every pitch. It varies in strength to correspond to all the
variations in the voice, and reproduces in the receiver not merely the
words that are spoken but the quality of the voice, so that the voice of
a friend can be recognized by telephone almost as well as if talking
face to face.

The same things are true of the wireless telegraph and telephone.
Instead of an electric current, let us say "a stream of electric waves."
Then we may say of the wireless everything that we have said of the wire
telegraph and telephone. In sending a message by wireless telegraph the
stream of electric waves flows when the key is pressed and stops when
the key is released. We have an interrupted stream of electric waves.
But an interrupted stream of waves cannot be used for a wireless
telephone any more than an interrupted current can be used for a
wire-telephone. There must be a constantly flowing stream of electric
waves, and these waves must be changed in strength and form by the sound
of the voice. Fig. 111 shows a wireless-telephone receiver in which
light is used to carry the message. The light acts on the receiver in
such a way as to reproduce the sound.

[Illustration: FIG. 111--RECEIVER OF BELL'S PHOTOPHONE
  An early idea in wireless telephony.]

In the wireless-telegraph receiver the interrupted stream of electric
waves makes and breaks the circuit of an electric battery. The
wireless-telephone receiver must not make and break a circuit, but it
must be sensitive to all the changes in the electric waves. One such
receiver is the audion, which we shall now describe.

The audion was invented by Dr. Lee de Forest. De Forest had taken the
degree of Doctor of Philosophy at Yale University, having written his
thesis for that degree on the subject of electric waves. He then entered
the employ of the Western Electric Company in Chicago, and while in this
position worked at night in his room on experiments with electric waves.

Here he found that a gas flame is sensitive to electric waves (Fig.
112). If a gas flame is made part of the circuit of an electric
battery, which includes also an induction-coil connected to a telephone
receiver, then when a stream of electric waves comes along there is a
click in the receiver. The waves change the resistance of the flame, and
so change the strength of the current. The flame is a simple audion. It
is the heated gas in the flame that responds to the electric waves.

[Illustration: FIG. 112--A GAS FLAME IS SENSITIVE TO ELECTRIC WAVES]

If instead of a gas flame an incandescent-light bulb is used having a
metal filament, and on either side of the filament a small strip of
platinum, a more sensitive receiver is obtained. This is the audion,
which is the distinguishing feature of the De Forest wireless telegraph
and wireless telephone. The metal filament is made white hot by the
current from a storage battery. The vacuum in the bulb is about the same
as that of the ordinary incandescent electric light. A very small
quantity of gas is therefore left in the bulb. The electrified particles
of gas respond more freely to electric waves in this bulb than in the
gas flame.

The De Forest wireless telephone was adopted for use in the United
States Navy shortly before the cruise around the world in 1908. Every
ship in the navy was equipped with the wireless telephone, enabling the
Admiral to talk with the officers of any vessel up to a distance of
thirty-five miles. The wireless telephone in use on a battle-ship is
shown in Fig. 113.

[Illustration: FIG. 113--CAPTAIN INGERSOLL ON BOARD THE U. S.
BATTLE-SHIP "CONNECTICUT" USING THE WIRELESS TELEPHONE]

    Wonders of the Alternating Current

Before the days of the electric current, men used the power of falling
water. The mill or factory using the water-power was placed beside the
fall. The water turned a great wheel, to which was connected the
machinery of the mill, It was not until the invention of the dynamo and
motor that water-power could be used at a great distance. If a hundred
years ago a man had said that the time would come when a waterfall could
turn the wheels of a mill a hundred miles away he would have been
laughed at. Yet this very thing has come to pass. Indeed, one waterfall
may turn the wheels of many factories, run street-cars, and light cities
up to a distance of a hundred miles and even more. The power of the
falling water goes out over slender copper wires from a great dynamo
near the fall to the motors in the factories and street-cars.

The falling water of Niagara has about five million horse-power. About
the hundredth part of this power is now being used. The water, falling
in a wheel-pit 141 feet deep, turns a great dynamo weighing 87,000
pounds with a speed of 250 turns per minute. A number of such dynamos
are used supplying an alternating current at a pressure of 22,000 volts,
the current alternating or changing direction twenty-five times per
second. Such a pressure is too high for the motors and electric lights,
but the current is carried at high pressure to the place where it is to
be used and there transformed to a current of low pressure. In carrying
a current over a long line, there is less loss if the current is carried
at high pressure. With an alternating current this can be done and the
current changed by means of a transformer to a current of low pressure.

A transformer is simply two coils of wire wound on an iron core. The
simplest transformer is the form used by Faraday when he discovered
electromagnetic induction. If instead of making and breaking a circuit
that flows only in one direction as Faraday did, we cause an alternating
current to flow through one of the coils, which we may call the primary,
each time the current changes direction in the primary the magnetic
field is reversed--that is, the end of the coil which was the north pole
becomes the south pole. This rapidly changing magnetic field induces a
current in the secondary coil. Each time the magnetic field of the
primary coil is reversed the current in the secondary changes direction.
Thus an alternating current in the primary induces an alternating
current in the secondary. One of these coils is of fine wire, which is
wound a great many times around the iron. The other is of coarser wire
wound only a few times around the iron. Suppose the current is to be
changed from high pressure to low pressure. Then the high-pressure
current from the line is made to flow through the coil of many turns,
and a current of low pressure is given out from the coil of few turns.
By changing the number of turns of wire in the coils we can make the
pressure whatever we please. If the pressure or voltage of the secondary
coil is less than that of the primary, we have a "step-down"
transformer. On the other hand, if we send the current from the line
wire through the coil of few turns, then we get a higher voltage from
the secondary coil than that of the line wire, and we have a "step-up"
transformer. The Niagara current is "stepped down" from 22,000 volts to
220 volts for use in motors.

An electric lamp may be lighted though not connected to any battery or
dynamo, but connected only to a coil of wire (Fig. 114). More than this,
the coil may be insulated so that no current can enter it from any other
coil or wire, and yet the lamp can be lighted. This can be done only by
means of an alternating current. If the coil to which the lamp is
connected is held in the magnetic field of an alternating current, then
another alternating current is induced in the coil, and this second
current flows through the lamp.

[Illustration: FIG. 114--INCANDESCENT ELECTRIC LAMP LIGHTED THOUGH NOT
CONNECTED TO ANY BATTERY OR DYNAMO]

We have already learned that a changing magnetic field induces a current
in a coil. Now the coil through which an alternating current is flowing
has a changing magnetic field all around it, and if the lamp-coil is
brought into this changing magnetic field an alternating current will
flow through the coil and the lamp. The insulation on the lamp-coil does
not prevent the magnetic field from acting, though it does prevent a
current from entering the coil. The current is induced in the coil
itself, and does not enter it from any outside source.

The transformer works in the same way, the only difference being that in
the transformer the two coils are on the same iron core. But in the
transformer the two coils are insulated so that no current can flow from
one coil to the other. When an alternating current and transformers are
used, the current that lights the lamps in the houses or on the streets
is not the current from the dynamo. It is a new current induced in the
secondary coil of the transformer by the magnetic field of the primary
coil.

A peculiar transformer which produces an alternating current that
changes direction millions of times in a second has been made by Nikola
Tesla. This current will do many wonderful things which no ordinary
current will do. It will light a room or run a motor without connecting
wires. It has produced an electric discharge sixty-five feet in length
(Figs. 115 and 116). Though this current is caused to flow by a pressure
of millions of volts, it may be taken with safety through the human
body. Strange as it may seem, the safety of this current is due to the
high pressure and the rapidity with which it changes direction. While
the current used at Sing Sing in executing criminals has a pressure of
about twenty-five hundred volts, a current having a pressure of a
million volts and alternating hundreds of thousands or millions of times
per second is harmless; With such a current the human body may become a
"live wire," and an electric lamp to be lighted held in one hand while
the other hand grasps the wire from the transformer.

[Illustration: FIG. 115--AN ELECTRIC DISCHARGE AT A PRESSURE OF
12,000,000 VOLTS, A CURRENT OF 800 AMPERES IN THE SECONDARY COIL]

[Illustration: FIG. 116.--AN ELECTRIC DISCHARGE SIXTY-FIVE FEET IN
LENGTH]

    X-Rays and Radium

A strange light which passes through the human body as readily as
sunlight through a window was discovered by Prof. Wilhelm Konrad
Roentgen, of the University of Würzburg. This light, which Professor
Roentgen named X-rays, is given out when an electric discharge at high
pressure passes through a certain kind of glass tube from which the air
has been pumped out until there is a nearly perfect vacuum.

X-rays were discovered by accident. Professor Roentgen was working at
his desk with one of the glass tubes when he was called to lunch. He
laid the tube with the electric discharge passing through it on a book.
Returning from lunch he took a photographic plate-holder which was under
the book and made some outdoor exposures with his camera. On developing
the plates a picture of a key appeared on one of them. He was greatly
puzzled at first, but after a search for the key found it between the
leaves of the book. The strange light from the electric discharge in the
glass tube had passed through the book and the hard-rubber slide of the
plate-holder and made a shadow-picture of the key on the photographic
plate. He tried the strange light in many ways, and found that it would
go through many objects. It would even go through the human body, so
that shadow-pictures of the bones and organs of the body could be
obtained. In Fig. 117 is shown a physician using X-rays. Fig. 118 is an
X-ray photograph of the eye.

[Illustration: FIG. 117--A PHYSICIAN EXAMINING THE BONES OF THE ARM BY
MEANS OF X-RAYS]

[Illustration: FIG. 118--X-RAY PHOTOGRAPH OF THE EYE
  The eye is above and to the left of the larger black circle. The smaller
black circle is a shot which has lodged back of the eye.]

Not long after the discovery of X-rays it was discovered that light very
much like the X-rays is given out by certain minerals. One of the most
interesting and the best known of these is radium. Radium gives out a
light somewhat like X-rays that will go through copper and other metals.
It does many other strange things. It gives out heat as well as light;
so much heat, in fact, that it is always about five degrees warmer than
the air around it. It continues to give out heat at such a rate that a
pound of radium will melt a pound of ice every hour. It can probably
keep this up for at least a thousand years. If this heat could be used
in running an engine, a hundred pounds of radium would run a
one-horse-power engine without stopping for many hundred years. The
power of Niagara might be replaced by the power of radium if an engine
that could use this power were invented. Fig. 119 is from a photograph
made with radium.

[Illustration: FIG. 119--PHOTOGRAPH MADE WITH RADIUM
  A purse containing a coin. The strange light from the radium goes
through the purse and the slide of the plate-holder and makes a
shadow-picture.]

The great inventor of the future may be able to use the heat of radium
or some new power now unknown. We have seen how, through the toil of
many years and the labors of many men, the great inventions of our age
have come into being. It may be that we are now witnessing other great
inventions in the making.




APPENDIX


BRIEF NOTES ON IMPORTANT INVENTIONS


             Aerial Navigation

     First air balloon--Montgolfier Brothers, France, 1783.

     First balloon ascension--Rozier, France, 1783.

     First gas balloon--Charles, France, 1783.

     First crossing of the English Channel in a balloon--Blanchard,
     1785.

     First successful dirigible balloon--La France, Renard and
     Krebs, France, 1884.

     First successful motor-driven aeroplane--Wright Brothers,
     United States; date of patent, 1906.

     First crossing of the English Channel by an aeroplane--Blériot,
     1909.

     First air-ship in regular passenger service--Count Zeppelin,
     Germany, 1910.


             Agriculture

     Plough with cast-iron mold-board and iron shares--James Small,
     Scotland, 1784.

     Grain-threshing machine--Andrew Meikle, England, 1788.

     McCormick reaper, first practical grain-harvesting
     machine--Cyrus H. McCormick, United States, 1831.

     Self-raker for harvesters--McCormick, 1845.

     Inclined platform and elevator in the reaper, to enable men
     binding the grain to ride with the machine--J. S. Marsh, United
     States, 1858.

     Barbed-wire fence introduced--United States, 1861.

     Self-binder, first automatic grain-binding device for the
     reaper--Jacob Behel, United States, 1864.

     Sulky plough--B. Slusser, United States, 1868.

     Twine-binder for harvesters--M. L. Gorham, United States, 1873.

     Improved self-binding reaper--Lock and Wood, United States,
     1873.

     Barbed-wire machine--Glidden and Vaughn, United States, 1874.

     Rotary disk cultivator--Mallon, United States, 1878.

     Steam-plough--W. Foy, United States, 1879.

     Combined harvester and thresher--Matteson, United States, 1886.

     Automobile mower--Deering Harvestor Company, United States,
     1901.


             Automobile

     First steam-automobile--Cugnot, France, 1769.

     First chain transmission of power in an automobile--Gurney,
     England, 1829.

     Application of gas-engine to road vehicles, beginning of the
     modern motor-car--Gottlieb Daimler and Carl Benz working
     independently, Germany, 1886. Daimler's invention consisted of
     a two-cylinder air-cooled motor. It was taken up in 1889, by
     Panhard and Levassor, of Paris, who began immediately the
     construction of the motor-car. This was the beginning of the
     motor-car industry.


             Bicycle

     First bicycle--Branchard and Magurier, France, 1779.

     Rear-driven chain safety bicycle--George W. Marble, United
     States, 1884.

     Bicycles first equipped with pneumatic tires--1890.


             Electrical Inventions

     William Gilbert, England, 1540-1603, called "the father of
     magnetic philosophy," first to use the terms "electric force,"
     "electric attraction," "magnetic pole."

     First electrical machine, a machine for producing electricity
     by friction--Otto von Guericke, Germany, about 1681.

     Discovery of conductors and insulators--Stephen Gray, England,
     1696-1736.

     First to discover that electric charges are of two
     kinds--Cisternay du Fay, France, 1698-1739; Du Fay was also the
     first to attempt an explanation of electrical action. He
     supposed that electricity consists of two fluids which are
     separated by friction, and which neutralize each other when
     they combine. This theory was more fully set forth by Robert
     Symmer.

     Leyden jar--Discovered first by Von Kleist in 1745. The same
     discovery was made and the Leyden jar brought to the attention
     of the public in 1746 by Pieter van Musschenbroek in Holland.

     Lightning-rod--Benjamin Franklin, 1732.

     Electroplating--Luigi Brugnatelli, Italy, 1805.

     Voltaic arc, a powerful arc light produced with a battery
     current--Sir Humphry Davy, England, 1808.

     Storage battery--Ritter, Germany, 1803. Platinum wires were
     dipped in water and a battery current passed through. Hydrogen
     collected on one wire and oxygen on the other. If the platinum
     wires were disconnected from the battery and connected with
     each other by a conductor, the two wires acted like the plates
     of a battery, and a current would flow for a short time in the
     new circuit.

     Electromagnetism discovered--H. C. Oersted, Denmark, 1819.

     Galvanometer, a coil of wire around a magnetic needle for
     measuring the strength of an electric current--Schweigger,
     Germany, 1820.

     Motion of magnet produced by an electric current--M. Faraday,
     England, 1821.

     Thermo-electricity, an electric current produced by heating the
     junction of two unlike metals--Discovered by Professor Seebeck
     England, 1821.

     Principles of electrodynamics, motion produced by an electric
     current--Ampère, France. Announced in 1823.

     Law of electric circuits, Ohm's law, current strength equals
     electromotive force divided by resistance of the
     circuit--George S. Ohm, Germany. Proven by experiment in 1826;
     mathematical proof published in 1827.

     Magneto-electric induction, induction of electric currents by
     means of a magnetic field--M. Faraday, England, 1831.

     Electric telegraph--Prof. S. F. B. Morse, United States, 1832.

     First telegram sent in 1844--Morse.

     Constant electric battery--J. P. Daniell, England, 1836.

     First electric motor-boat--Jacobi, Russia, 1839.

     Induction-coil--Rhumkorff, Germany, 1851.

     Duplex telegraph, first practical system--Stearns, United
     States, about 1855-1860.

     Storage battery, lead plates in sulphuric acid--Gaston Planté,
     France, 1859.

     Telephone, make-and-break system, first electrical transmission
     of speech--Philip Reiss, Germany, 1860.

     Atlantic cable laid--Cyrus W. Field, 1866.

     Dynamo, armature coil rotates in the field of an electromagnet,
     armature supplies current for the electromagnet as well as for
     the external circuit--William Siemens, Germany, 1866.

     Gramme ring armature for dynamo--Gramme, France, 1868.

     Theory that light consists of electromagnetic
     waves--Clerk-Maxwell, England, 1873.

     Quadruplex telegraph, sending four messages over one wire at
     the same time--Edison, 1873.

     Siphon recorder for submarine telegraph, sensitive to very
     feeble currents--Sir William Thomson, England, 1874.

     Telephone, varying current, first practical working
     telephone--Alexander Graham Bell, United States, 1876.

     Electric candle, beginning of present arc light--Paul
     Jablochkoff, Russia, 1876.

     Telephone transmitter of variable resistance--Emil Berliner and
     Edison working independently, United States, 1877. Edison used
     carbon contacts, Berliner used metal contacts.

     Brush system of arc lighting--1878.

     Incandescent electric lamp with carbon filament--Edison, 1878.

     First electric locomotive--Siemens, Germany, 1879.

     Blake telephone transmitter--Blake, United States, 1880.

     Storage battery, lead grids filled with active material--Faure,
     France, 1881.

     Electric Welding--Elihu Thompson, United States, 1886.

     Electric Waves discovered by experiment--Heinrich Hertz,
     Germany, 1888.

     Coherer for receiving electric Waves--Edward Branly, France,
     1890.

     X-rays--Discovered by Prof. W. C. Roentgen, Germany; announced
     to the public in 1895.

     Wireless telegraphy--G. Marconi, Italy, 1896.

     Nernst electric light, a clay capable of conducting electricity
     when heated is used; it becomes incandescent without a
     vacuum--Walter Nernst, Germany, 1897.

     Radium discovered by Madame Curie, France, 1898.


             Explosives

     Gunpowder--Inventor and date unknown.

     Guncotton--Schönbein, Germany, 1845.

     Nitroglycerine--Sobrero, 1847.

     Explosive gelatine--A. Nobel, France, 1863.

     Dynamite--A. Nobel, France, 1866.

     Smokeless powder--Vielle, France, 1866.


             Firearms and Ordnance

     Spirally grooved rifle barrel--Koster, England, 1620.

     Breech-loading shot-gun--Thornton and Hall, United States,
     1811.

     The revolver; a device "for combining a number of long barrels
     so as to rotate upon a spindle by the act of cocking the
     hammer"--Samuel Colt, United States, 1836.

     Breech gun-lock, interrupted thread--Chambers, United States,
     1849.

     Magazine gun--Walter Hunt, United States, 1849.

     Breech-loading rifle--Maynard, United States, 1851.

     Iron-clad floating batteries first used in Crimean War--1855.

     Breech-loading ordnance--Wright and Gould, United States, 1858.

     Revolving turret for floating batteries--Theodore Timby, United
     States, 1862.

     First iron-clad floating battery propelled by steam: the
     _Monitor_--John Ericsson, United States, 1862.

     Gatling gun--Dr. R. J. Gatling, United States, 1862.

     Automatic shell-ejector for revolver--W. C. Dodge, United
     States, 1865.

     Torpedo--Whitehead, United States, 1866.

     Disappearing gun-carriage--Moncrief, England, 1868.

     Rebounding gun-lock--L. Hailer, United States, 1870.

     Magazine rifle--Lee, United States, 1879.

     Hammerless gun--Greener, United States, 1880.

     Gun silencer, to be attached to barrel of gun; gun can be fired
     without noise--Maxim, 1909.


             Gas Used for Light and Power

     Gas first used for illuminating purposes--William Murdoch,
     England, 1792.

     First street gas-lighting in England--F. A. Winsor, 1814.

     Gas-meter--S. Clegg, England, 1815.

     Water-gas, prepared by passing steam over white-hot anthracite
     coal--First produced in England in 1823.

     Illuminating water-gas--Lowe, United States, 1875.

     Gas-engine, 4-cycle, beginning of modern gas-engine--Otto and
     Langen, Germany, 1877.

     Incandescent gas-mantle--Carl A. von Welsbach, Austria, 1887.


            Iron and Steel

     Blast-furnace, beginning of iron industry--Belgium, 1340.

     Use of coke in blast-furnace--Abram Darby, England, about 1720.

     Puddling iron--Henry Cort, England, 1783-84.

     Process of making malleable-iron castings--Lucas, England,
     1804.

     Hot-air blast for iron furnaces--J. B. Neilson, Scotland, 1828.

     The galvanizing of iron--Henry Craufurd, England, 1837.

     Process of making steel, blowing air through molten pig-iron to
     burn out carbon, then adding spiegel iron; first production of
     cheap steel--Sir Henry Bessemer, England, 1855.

     Regenerative furnace, a gas-furnace in which gas and air are
     heated before being introduced into the furnace, giving an
     extremely high temperature--William Siemens, England, 1856.

     Open-hearth process of making steel--Siemens-Martin, England,
     1856.

     Nickel steel, much stronger than ordinary steel, used for
     armorplate--Schneider, United States, 1889.


             Mining

     Miners' safety-lamp--Sir Humphry Davy, England, 1815.

     Compressed-air rock-drill--C. Burleigh, United States, 1866.

     Diamond rock-drill, a tube of cast-steel with a number of black
     diamonds set at one end. The machine cuts a circular groove,
     leaving a core inside the tube. This core is brought to the
     surface with a rod, and the powdered rock is washed out by
     water forced down the tube and flowing up the sides of the
     hole. The drill does not have to stop for cleaning out--Herman,
     United States, 1854.


             Photography

     First photographic picture, not permanent--Thomas Wedgewood,
     England, 1791.

     Daguerreotype, first developing process--Louis Daguerre,
     France, 1839.

     First photographic portraits, daguerreotype process--Prof. J.
     W. Draper, United States, 1839.

     Collodion process in photography--Scott Archer, England, 1849.

     Photographic roll films--Melhuish, England, 1854.

     Dry-plate photography--Dr. J. M. Taupenot, 1855.

     Photographic emulsion, bromide of silver in gelatine, basis of
     present rapid photography--R. L. Maddox, England, 1871.

     Hand photographic camera for plates--William Schmid, United
     States, 1881.


             Printing

     First printing with movable types in Europe and first
     printing-press--Guttenberg, Germany, about 1445.

     Screw printing-press--Blaew, Germany, 1620.

     First newspaper of importance--_London Weekly Courant_, 1625.

     Stereotyping, making plates from casts of the type after it is
     set up--William Ged, Scotland, 1731.

     First practical steam rotary printing-press, paper printed on
     both sides, 1800 impressions per hour--Frederick Koenig,
     Germany, 1814.

     Printing from curved stereotype plates--H. Cowper, England,
     1815.

     Hoe's lightning press, 2000 impressions per hour--R. Hoe,
     United States, 1847.

     Printing from a continuous web, paper wound in rolls, both
     sides printed at once--William Bullock, United States, 1865.

     "Straightline newspaper perfecting" press, prints 100,000
     eight-page papers per hour--Goss Company, United States.

     Linotype machine. The operator uses a keyboard like that of a
     typewriter. The machine sets the matrices which correspond to
     the type, casts the type in lines from molten metal, delivers
     the lines of type on a galley, and returns the matrices to
     their appropriate tubes. It does the work of five men setting
     type in the ordinary way--Othmar Mergenthaler, United States,
     1890.


            Steam Navigation

     First steamboat in the world--Papin, River Fulda, Germany,
     1705.

     First steamboat in America--John Fitch, Delaware River, 1783.

     First passenger steamboat in the world, the _Clermont_--Robert
     Fulton, Hudson River, 1807.

     First steamer to cross the Atlantic, the _Savannah_, built at
     New York--First voyage across the Atlantic, 1819.

     The screw propeller first used on a steamboat--John Ericsson,
     United States, about 1836.

     Compound engines adopted for steamers--1856.

     First turbine-steamer, the _Turbinia_--Parsons, 1895.

     First mercantile steam-turbine ship, the _King Edward_--Denny
     and Brothers, England, 1901.

    Steam Used for Power and Land Transportation

     First steam-engine with a piston--Denys Papin, France, 1690.

     First practical application of the power of steam, pumping
     water--Thomas Savery, England, 1698.

     Double-acting steam-engine and condenser--James Watt, Scotland,
     1782.

     Steam-locomotive first used to haul loads on a
     railroad--Richard Trevethick, England, 1804.

     First passenger steam railway, the "Stockton &
     Darlington"--George Stephenson, England, 1825.

     First steam-locomotive in the United States, the "Stourbridge
     Lion"--1829.

     Link motion for locomotives--George Stephenson, England, 1833.

     Steam-whistle, adopted for use on locomotives--George
     Stephenson, 1833.

     Steam-hammer--James Nasmyth, Scotland, 1842.

     Steam-pressure gauge--Bourdon, France, 1849.

     Corliss engine--G. H. Corliss, United States, 1849.

     First practical steam-turbine--C. A. Parsons, England, 1884.


             Textile Industries

     Flying shuttle, first important invention in weaving, leading
     to modern weaving machinery--John Kay, England, 1733.

     Spinning-jenny--James Hargreaves, England, 1763.

     Power loom--James Cartwright, England, 1785.

     Cotton-gin, for separating the seeds from the fibre, gave a new
     impetus to the cotton industry. The production of cotton
     increased in five years from 35,000 to 155,000 bales--Eli
     Whitney, United States, 1792.

     Pattern loom, for the weaving of patterns--M. J. Jacquard,
     France, 1801.

     Application of steam to the loom--William Horrocks, England,
     1803.

     Knitting-machine--Brunel, England, 1816.

     Sewing-machine--Elias Howe, United States, 1846.

     Mercerized cotton--John Mercer, England, 1850.

     Process of making artificial silk--H. de Chardonnet, France,
     1888.


            Wood-Working

     Circular wood-saw--Miller, England, 1777.

     Wood-planing machine--Samuel Benthem, England, 1791.

     Wood-mortising machine--M. J. Brunel, England, 1801.

     Band wood-saw--Newberry, England, 1808.

     Lathe for turning irregular wood forms--Thomas Blanchard,
     United States, 1819.

     Improved planing-machine--William Woodworth, United States,
     1828.


             Miscellaneous

     First fireproof safe--Richard Scott, England, 1801.

     Steel pen, quill pen used up to this time--Wise, England, 1803.

     First life-preserver--John Edwards, England, 1805.

     Calculating machine--Charles Babbage, England, 1822.

     First friction matches--John Walker, United States, 1827. Flint
     and steel were used for starting fires before matches were
     invented.

     First portable steam fire-engine--Brithwaite and Ericsson,
     England, 1830.

     Vulcanizing of rubber--Charles Goodyear, United States, 1839.

     Pneumatic tire--R. W. Thompson, England, 1845.

     Time-lock for safes--Savage, United States, 1847.

     Match-making machinery--A. L. Denison, United States, 1850.

     American machine-made watches--United States, 1850.

     Safety matches--Lundstrom, Sweden, 1855.

     Sleeping-car--Woodruff, United States, 1856.

     Printing-machine for the blind, origin of the
     typewriter--Alfred E. Beach, United States, 1856.

     Cable-car--E. A. Gardner, United States, 1858.

     Driven well, an iron tube with the end pointed and perforated
     driven into the ground--Col. N. W. Green, United States, 1861.

     Passenger elevator--E. G. Otis, United States, 1861.

     First practical typewriter--C. L. Sholes, United States, 1861.

     Railway air-brake, use of air-pressure in applying brakes to
     the wheels of a car. A strong spring presses the brake against
     the wheels. Air acts against the spring and holds the brake
     away from the wheels. To apply the brake, air is allowed to
     escape, reducing the pressure and allowing the spring to
     act--George Westinghouse, United States, 1869.

     Store-cash carrier--Dr. Brown, United States, 1875.

     Roller flour-mills--F. Wegman, United States, 1875.

     Kinetoscope, moving-picture machine--Edison, 1893.




INDEX


    Aeroplane, 184.

    Air-pressure, 23.

    Air-pump, 20.

    Air-ships, 173.

    Air thermometer, 13.

    Alternating current, wonders of, 225.

    Amber, 8.

    Ampère, 67, 111.

    Arago, 69.

    Archimedes, 1, 12;
      inventions of, 7.

    Archimedes' principle, 6, 12.

    Arc light, 120.

    Armature, 101, 103, 104.


    Balloons, 174.

    Barometer, mercury, 19, 25;
      water, 23.

    Battle of Syracuse, 2.

    Bell, Alexander Graham, 141.

    Blake transmitter, 146.

    Blériot, 190.

    Boyle, 23.

    Branly, 214.


    Cannon experiment, Rumford's, 59.

    Cog-wheels, first used, 8.

    Coherer, 214.

    Colors in sunlight, 31.

    Condenser in steam-engine, 40.

    Conductors, electrical, 44.

    Controller, 116.


    Daniell cell, 89, 127.

    Davy, 56, 61, 96.

    De Forest, 224.

    Diamonds, manufacturing, 206.

    Drum armature, 104.

    Dry battery, 91.

    DuFay, 45.

    Dumont, 179.

    Duplex telegraphy, 136.

    Dynamo, 55, 79, 81, 96, 99, 100, 105, 111;
      series wound, 105;
      shunt wound, 107;
      compound wound, 108.


    Edison, 95, 105, 114, 121.

    Electrical machine, 23, 44, 45, 83.

    Electric battery, 53, 62, 84, 89.

    Electric charge, two kinds, 45.

    Electric current, 50, 69, 73, 74, 82, 96;
      magnetic action of, 66, 68;
      produced by a magnet, 72.

    Electric furnace, 205.

    Electricity, 8, 50;
      theories of, 49;
      speed of, 133.

    Electric lighting, 97, 118.

    Electric motor, 71, 97, 111.

    Electric power, 111.

    Electric railway, 112.

    Electric waves, 212.

    Electromagnet, 100, 126, 143.

    Electromagnetism, 65.


    Faraday, 55, 63, 100, 111;
      electrical discoveries, 64.

    Force-pump, 8.

    Franklin, 43, 45, 46, 65.


    Galileo, 9, 63;
      experiment with falling shot, 12.

    Galvani, 50.

    Galvanometer, 74, 75.

    Gas-engines, 150.

    Glider, 186.

    Governor, fly-ball, 42.

    Gramme-ring armature, 103.

    Gravitation, 30.

    Gravity cell, 91.

    Gray, Stephen, 44.

    Guericke, 20, 35.

    Gyroscope, 200.


    Heat, 59.

    Henry, Joseph, 97, 127.

    Hero, 8, 164;
      engine, 164.

    Hiero, King of Syracuse, 1, 6.

    Horse-power, 40.

    Hydraulic press, 26.


    Incandescent light, 121.

    Indicator, 41.

    Induction-coil, 76, 82, 99.

    Induction, electrical, 74.

    Insulators, 44.

    Inventions of the ancient Greeks 7;
      of the nineteenth century, 88.


    Kite experiment, Franklin's, 46.

    Kites, 27.


    Leyden jar, 43.

    Lightning-rod, 48.

    Lines of force, 99.

    Liquid air, 203.

    Locomotive, electric, 114;
      steam, 155.


    Magdeburg, 21.

    Magnetic field, 80, 99.

    Magnets, 8, 130.

    Marconi, 215.

    Mayer, Robert, 61, 85.

    Mercury vapor light, 125.

    Microscope, 18.

    Miner's safety lamp, 61.

    Monorail car, 201.

    Morse, 128.


    Napoleon, 62.

    Newcomen, 34, 36.

    Newcomen's engine, 36.

    Newton, 27.

    Niagara, 227.


    Oersted, 65, 71, 111, 126.


    Papin, 35.

    Papin's engine, 35.

    Pascal, 25.

    Pendulum clock, 10, 12.

    Perpetual motion impossible, 87.

    Phonograph, 147.

    Principle of Work, 19.

    Prism, 31.

    Pump, 8, 19.


    Radium, 232.

    Reis, Philip, 141.

    Relay, 130.

    Roentgen, 232.

    Royal institution, 56, 61.

    Rumford, 57, 59.

    Rumford's cannon experiment, 59.


    Safety-lamp, 62.

    Screw propeller, 171.

    Siemens, 100.

    Spinning tops, 199.

    Steam-engine, 8, 25, 34.

    Steam locomotive, 155.

    Steam pressure, 23.

    Stephenson, 156.

    Storage battery, 93.

    Sturgeon, 97, 127.

    Submarines, 190.

    Suction-pump, 8.

    Symmer, Robert, 49.


    Telegraph, 96, 126;
      wireless, 208.

    Telephone, 140;
      wireless, 221.

    Telescope, invention of, 15;
      Newton's, 32.

    Tesla, 231.

    Thermometer, air, 13.

    Torpedo, 192.

    Torricelli, 19, 35.

    Transformer, 80, 82, 99, 227.

    Turbine, 163.


    University of Padua, 13.

    University of Pisa, 10, 12.


    Valve-gear, 37, 162.

    Volta, 53, 63, 89.

    Voltaic battery, 53, 89.


    Water-clock, 8, 29.

    Water-wheel, 165.

    Watt, James, 34.

    Watt's engine, 38.

    Wireless telegraph, 208.

    Wright aeroplane, 188.


    X-rays, 232.


    Zeppelin, 180.


                                THE END