Transcriber’s Notes:

Text enclosed by underscores is in italics (_italics_), and text
enclosed by equal signs is in bold (=bold=).

The whole number part of a mixed fraction is separated from the
fractional part with -, for example, 2-1/2.

Additional Transcriber’s Notes are at the end.




How to Become an Inventor.


  CONTAINING
  Experiments in Photography, Hydraulics,
  Galvanism and Electricity,
  MAGNETISM, HEAT,
  AND THE
  Wonders of the Microscope.

  ALSO GIVING
  Instruction in the Use of Tools
  AND
  OPTICAL INSTRUMENTS.

  NEW YORK:
  FRANK TOUSEY, Publisher,
  29 WEST 26TH STREET.

       *       *       *       *       *

Entered according to Act of Congress, in the year 1898, by

FRANK TOUSEY,

in the Office of the Librarian of Congress at Washington, D.C.




How to Become an Inventor.


Nothing is more useful to a youth than to be able to do a little
carpentering. To be handy with a chisel and saw, a nail and a hammer,
saves many a dollar in the course of the year. If you call in a
carpenter for a little work he is sure to spin out a “regular job.” I
remember once buying some oak saplings, which cost me fifteen cents
a stick; and wanting to build a summer-house, I required eight of
them to be sawn through, so I applied to a carpenter, and the sticks
were cut, but, to my astonishment, four dollars was charged for this
little “job,” although the wood cost me only one dollar and thirty
cents. I found out afterwards that the proper price for sawing would
have amounted to about one dollar, so that three dollars profit was
clapped on for the benefit of my experience. I just mention this to
show my young friends that if they wish to make summer-houses for their
gardens, cages for their birds, fowl-houses, rabbit-hutches, or boxes
for their books, they must learn to make them for themselves. I shall
therefore offer them a little advice upon “carpentering.”


THE SHOP AND BENCH.

Endeavor to procure some small outhouse, in which you may erect what is
called a carpenter’s or joiner’s bench. These may very often be bought
second-hand, or if not, can easily be procured at a reasonable rate.
I am very particular in recommending a bench, as without it you will
find many obstacles to your work. You must also provide yourself with
a set of tools,--gimlets, hammers, planes, saws, gouges, files, nails,
screws, and such articles of use.

The bench is composed of a platform or top, supported by four stout
legs; supplied with a bench hook; this ought to be fitted in tight, so
as to move up and down with a hammer only. The use of it is to keep any
wood steady you may have to plane; the bench screw is used for keeping
any wood firm and steady you may have to saw, which is to be put in
the grip and screwed tight. Sometimes the edges of wood require to be
planed, and then the wood is put in the grip or cheeks of the bench and
held tight while you plane it. Make holes in the side of the bench, for
the insertion of a movable pin to support the end of the board you
have to plane or saw, which is not in the screw. The height of your
bench should be about 2 feet 8 inches. The common length is from 10 to
12 feet, and the breadth about 3 feet 6 inches.

The jack plane is the first to be used. It is about 17 inches in
length, and is used to take the rough parts from a piece of wood. It
should be held steadily by fixing the right hand at the handle, and the
left over the top and side, and pushed forward on the wood, when the
knife will take off a shaving which runs through the hole, and falls on
the side. In using the plane the endeavor should be to take off a clean
shaving, which is done by using the instrument uniformly and steadily
over every surface to be planed.

There is another kind of plane, called the trying plane, having a
double top or handle. It is used to regulate and smooth to a higher
degree, the surface of the wood that had previously been smoothed from
the rough by the jack plane. Its length is about 22 inches, and it is
broader than the jack plane. There is another plane called the _long_
plane, which is used for facing a piece of stuff, which it does with
the greatest exactness; its length is about 2 feet 4 inches. There is
also the joiner’s plane, which is the longest of all the planes, being
30 inches long. But the most handy of the planes to the boy carpenter
is the smoothing plane. It is the last plane used in joining, and gives
the utmost degree of smoothness to the surface of a piece of finished
work; it is about 7 inches in length, the sides of the stock are
curved, and resemble in figure a coffin; it is used in a similar way to
the other.


SAWS.

There are many kinds of saws, but the most useful one is what is called
the “hand saw.” It has a blade or plate about 28 inches long; the teeth
of which are so formed as to allow you to cut the wood crossways as
well as lengthways. The handle of the saw is made so as to allow a full
yet free grasp of the hand, either for a pull or a thrust.

The _panel saw_. This saw has a plate nearly of the same size as a hand
saw, and is used for cutting very thin boards, which the rough teeth of
the hand saw would not cut through without breaking them.

The _tenon saw_ is of a different shape to the others, and is made
to cut across the grain of the wood so as to leave the ends nicely
even, that it may fit to the piece it is joined to, which is called a
shoulder, being that part which comes in contact with the fiber of the
wood. To do this it requires that the teeth should be much smaller,
and they are therefore placed so close as eight or ten to the inch,
according to the length of the blade.

The _dovetail saw_. There is another most useful saw it would be of
advantage for the young carpenter to have, namely, the dovetail saw.
It is about 9 inches long, and contains at least fifteen teeth in the
inch. It is used for cutting the dovetails of boxes. Its plate is very
thin, and it requires some care in using. It has a back for the purpose
of strength, formed of a thin piece of brass or iron, let in so as to
give the blade the requisite firmness necessary in using it.

The _compass saw_. The plate of this kind of saw is very narrow, and
not more than one inch wide at the broadest part, gradually diminishing
to about a quarter of an inch at the lower end. It is about 15 inches
in length, and used for cutting a piece of wood into a circular form,
and the plate being narrow allows it to follow the foot of the compass
to a very small diameter.

The _keyhole saw_. The keyhole saw is much smaller than the above. It
is used for cutting short curves, small holes, &c., such as a keyhole.
The handle is the same form as that of the chisel, a small slit being
cut through from end to end. It has a screw on one side, in order that
the blade may be set to any length, according to the circumference of
the hole to be cut.


THE SPOKE SHAVE.

This is a very useful tool. It is employed for smoothing the edges of
round pieces, or other ends requiring to be shaved down. It is a narrow
plane made of boxwood, and has generally a steel blade let into it to
cut; it is used by taking hold of each end with a hand, and moving it
to and fro over the wood to be shaved down.


STOCK AND BITS.

There are about thirty-six bits to a set, all of different shapes
and sizes; but our young friends need not get quite so many; if they
provide themselves with a couple of a medium size, this will be
sufficient, such as the center bit and the auger bit. The center bit
will cut holes varying from a quarter of an inch to three quarters of
an inch in diameter, and is used by pressing the knob end against the
chest, and twirling the center part round with the hand. It cuts a hole
very clean, leaving it quite smooth inside. The auger bit is for the
same purpose, and is used in the same manner. Another bit, called the
taper shell bit, is used for making holes wider, and is a very useful
implement.


HOW TO MAKE A WHEELBARROW.

One of the handiest things in a garden is a wheelbarrow, and one of the
prettiest for the young carpenter to exercise his ingenuity upon. To
make one, take a wide plank or board about an inch and a quarter thick.
Proceed to your bench, and having fitted it to its proper position,
take your jack plane and plane off the rough, next use your smoothing
plane to make it smooth. Then take your pencil and draw upon its side
the figure of a wheelbarrow. Then take your compass saw and cut round
the marks you have made: to do this you will have to fix your board
in the screw of your bench. When this is done take your spoke shave,
and shave the edges all round till they are very smooth and even, and
you have one side of your barrow. Lay this on another piece of board,
and mark the shape of it with your pencil; cut and shave it exactly
as you did the first side, so that when finished the two will exactly
correspond; then cut a piece off another board for the back and front
of the barrow, by the same method you cut the sides, and plane and
finish them up in a similar way. Cut some tenons at the end of each
exactly to correspond with the mortices on the sides, let them be a
trifle larger than the mortices, so that they will drive in tight. Then
cut the bottom out neatly, and nail it to the sides. Having proceeded
thus far, cut out the legs of your barrow, and nail one on each side.
Give each leg a shoulder for the sides to rest upon.

_To make the wheel._ Take a piece of board, and strike a circle upon
it the size you wish your wheel to be of, and with the compass saw cut
close round to the stroke; cut out a square hole in the center for the
nave to join. Then get the blacksmith to put an iron rim round the
wheel to keep it from splitting, and a round pin in each side of the
nave, and put a staple in each side of the barrow to keep the wheel in
its place. Paint the whole of any color you choose, and you will have a
wheelbarrow.


THE WAY TO MAKE A BOX.

First ascertain the size you wish your box to be of. Then cut off your
stuff, but take care to cut it a quarter of an inch longer than the
size of your box from outside to outside. Should you want it deeper or
broader than the length of a deal, the widest of which is generally
only eleven inches; suppose, for instance, you wish your box to be
18 inches deep, and you have only 9-inch deal to make it with, you
will of course have to join two together, or make what is called in
carpentering a _gluejoint_. First, then, after you have cut off your
stuff, take your jack plane and “scuffle the rough off,” then put your
board edgeways into the bench-screw, and take your trying plane or
long plane to get the edge of the deals that are to be glued together
perfectly straight and even; and lastly use the joiner plane, which
will take off a nice uniform shaving of the whole length of the board.
Proceed exactly in the same manner with the other board to be joined
to the first. Then, after having made each thoroughly smooth, clap the
two together and see if they will lie close in every part; if not you
must plane them till they do, taking care to plane the edges perfectly
square, or at right angles to the surface of the board, for if you are
not careful in this particular, when your boards are glued together
they will be of this form. When you have joined them properly for
glueing, let your glue be nicely hot and not too thick, and hold both
edges of the boards together so that you can with a brush put the glue
on both at one time, put the two together very quickly, let one of them
be in the bench-screw, and while there rub the other backwards and
forwards until the glue sets, which it will soon do if well joined. Let
the whole dry, and then the glued part will be as strong as any other
part of the board.

After your sides, ends, bottom, and top are thus prepared, you must
then plane them up nicely, so that they are perfectly smooth and
straight. Use first the jack plane, then the trying plane. When this
is done you have to proceed to a nice little job, namely, to dovetail
the corners together so as to form your box. In this process much
depends upon the planing and squaring of the stuff, for if you have not
done this nicely the dovetailing will be very imperfectly performed.
Assuming that everything has been well done, then take the two ends of
the box, and see that each is perfectly square and true to the other.
Then allow one-eighth of an inch more than the thickness of your sides,
and set out the ends, squaring it over on both sides, which when the
dovetails are cut out will form the inside of the box.


TO CUT THE DOVETAILS.

Take one “end-piece” of the box, and place it endways into the
bench-screw, and mark out the dovetails on the edge of the board
inside, then with your dovetail saw cut in into the marks down to the
lines squared over on the flat side. Then with a chisel cut out that
part of the wood that is crossed, and leave the other part, this being
the part which will form the pins or tails. Then take one side of your
box and lay it flat on the bench, the inside uppermost; then place the
end you have cut on it, keeping the edges flush, and mark round the
shape of the pins, which will leave their form on the side piece, the
black places being the mortices which are to be cut out. In cutting out
these you must be careful to cut within side of the stroke, so that the
mortices will be a little smaller than the pins, which will admit of
their being driven in quite tight, and will allow the glue to adhere to
them (for you have to glue these when you fix them). When you have thus
put the ends and sides together let them stand till the glue gets dry,
then take your planes and plane the quarter of an inch off the pins
which you allowed to be a little longer than the length of the box, and
you have then made the body of your box.


THE BOTTOM OF THE BOX.

Cut your bottom the exact size of the box, nail the bottom on, and “get
out” a piece of wood (by cutting and planing in the usual manner) to
nail round so as to form a skirting to it, and at the same time hide
the joints of the bottom; “get out” a similar piece of wood to nail
round the top which will form the lid. Then get a pair of box joints
and a lock, and having put them on by a stroke of your own ingenuity,
you will have a “box.”




GALVANISM, OR VOLTAIC ELECTRICITY.


          “To play with fire
  They say is dangerous; what is it then
  To shake hands with the lightning, and to sport
  With thunder?”--TYLER.

Galvanism, or electricity of quantity, in contradistinction to
frictional electricity, called electricity of intensity, owes its name
to the experiments on animal irritability made in 1790 by M. Galvani,
a professor of anatomy at Bologna. These experiments were suggested by
the following circumstances.


ORIGIN OF GALVANISM.

It happened that the wife of Galvani, who was consumptive, was advised
to take as an article of food some soup made of the flesh of frogs.
Several of these creatures were killed and skinned, and were lying on
the table in the laboratory close to an electrical machine, with which
a pupil of the professor was making experiments. While the machine
was in action, he chanced to touch the bare nerve of the leg of one
of the frogs with the blade of the knife that he had in his hand,
when suddenly the whole limb was thrown into violent convulsions.
Galvani was not present when this occurred; but being informed of it,
he immediately set himself to investigate the cause. He found that it
was only when a spark was drawn from the prime conductor, and when the
knife or any other good conductor was in contact with the nerve, that
the contracting took place; and after a time he discovered that the
effect was independent of the electrical machine, and might be equally
well produced by making a metallic communication between the outside
muscle and the crural nerve.


SIMPLE EXPERIMENT TO EXCITE GALVANIC ACTION.

If the young experimenter will obtain a piece of zinc of the size
of half a dollar and place it on the top of his tongue, and place a
half-dollar beneath it, and bring the edges of the half-dollar and zinc
in contact in front of his tongue, he will notice a peculiar sensation
in the nerves of this organ, and some taste will be imparted to his
mouth at the moment of contact.


WITH METAL PLATES IN WATER.

If we take two plates of different kinds of metal, platinum (or copper)
and zinc for example, and immerse them in pure water, having wires
attached to them above, then if the wire of each is brought into
contact in another vessel of water, a galvanic circle will be formed,
the water will be slowly decomposed, its oxygen will be fixed on the
zinc wire, and at the same time a current of electricity will be
transmitted through the liquid to the platina or copper wire, on the
end of which the other element of water, namely, the hydrogen, will
make its appearance in the form of minute gas bubbles. The electrical
current passes back again into the zinc at the points of its contact
with the platina, and thus a continued current is kept up, and hence
it is called a galvanic circle. The moment the circuit is broken by
separating the wires the current ceases, but is again renewed by
making them touch either in or out of the water. If a small quantity
of sulphuric acid be added to the water, the phenomenon will be more
apparent. The end of the wire attached to the piece of platinum or
copper is called the positive pole of the battery, and that of the wire
attached to the zinc the negative pole.

The current of electricity here generated will be extremely feeble;
but this can be easily increased by multiplying the glasses and the
number of the pieces of metal. If we take six such glasses instead of
one, partially fill them with dilute sulphuric acid, and put a piece
of zinc and copper into each, connecting them by means of copper wire
from glass to glass through the whole series, a stronger current of
electricity will be the result. The experimenter must be careful not to
let the wire and zinc touch each other at the bottom of the tumblers,
and must also remember that the copper of glass 1 is connected with the
zinc of glass 2, and so on.


TO MAKE A MAGNET BY THE VOLTAIC CURRENT.

To effect this, make a connection between the poles of the above or any
excited battery with the two ends of a wire formed into a spiral coil,
by bending common bonnet-wire closely round a cylinder, or tube, of
about an inch in diameter; into this coil introduce a needle or piece
of steel wire, laying it lengthways down the circles of the coil. In
a few minutes after the electric fluid has passed through the spiral
wire, and consequently round the needle or wire, the latter will be
found to be strongly magnetized, and to possess all the properties of a
magnet.


EFFECTS OF GALVANISM ON A MAGNET.

If a galvanic current, or any electric current, be made to pass along a
wire under which, and in a line with it, a compass is placed, it will
be found that the needle will no longer point north and south, but will
take a direction nearly across the current, and point almost east and
west.


CHANGE OF COLOR BY GALVANISM.

Put a teaspoonful of sulphate of soda into a cup, and dissolve it in
hot water; pour a little cabbage blue into the solution, and put a
portion into two glasses, connecting them by a piece of linen or cotton
cloth previously moistened in the same solution. On putting one of the
wires of the galvanic pole into each glass, the acid accumulates in the
one, turning the blue to a red, and the alkali in the other, rendering
it green. If the wires be now reversed, the acid accumulates eventually
in the glass where the alkali appeared, while the alkali passes to the
glass where the acid was.


THE GALVANIC SHOCK.

If the ends of the wires of a small galvanic battery are connected with
a proper electro-magnetic coil, which may now be purchased at a very
cheap rate, and the wires from the coil be placed in separate basins
of water, then, on dipping the fingers of each hand in the basin, a
smart shock will be felt, with a particular aching accompanied with
trembling. With a strong battery and larger coil this effect is felt as
high as the shoulders. The shock will also be felt by simply holding
the wires of a powerful galvanic battery, one in each hand, provided
the hands be moistened with salt and water. Several persons may receive
the shock from the battery and coil together by joining hands.


THE ELECTROTYPE.

The electro-galvanic current has in no case been more interestingly
employed than in the process of electrotyping. It consists of a mode
of obtaining the copy of coins, medals, engraved plates, and other
objects, which may be easily illustrated.


HOW TO MAKE AN ELECTROTYPE APPARATUS.

Take an earthen jar and a porous tube; fill the tube with ten parts of
water and one of sulphuric acid; put it into the jar, into which pour
as much of a solution of sulphate of copper (blue vitriol) as will
fill three parts of it; place in the tube a piece of zinc, to which a
copper wire is soldered and bent round, so that one end be immersed in
the sulphate of copper; and a deposit of the copper will be immediately
formed upon the wire. If there be plenty of acid and water, so as to
allow of the action enduring for a long time, this process will go on
till it has deposited all the copper. This is the principle upon which
electrotyping proceeds--a principle referable to electro-chemical
decomposition.


TO OBTAIN THE COPY OF A COIN OR MEDAL.

Never place the original medal in the apparatus, or the deposited
copper may adhere so tightly to it that the removal destroys the beauty
of the medal. Having taken an impression in sealing-wax, cover the
latter with black-lead, and attach a wire so that it is in contact
with the black-lead. To the wire and cast thus arranged a piece of
sheet or cast zinc, amalgamated with mercury, must be attached, and
we are at once furnished with the materials for the battery, as the
object to be copied supplies the place of the copper. The medal must
always be placed horizontally. Now let the apparatus be charged with
the solution, by pouring into the outer vessel a portion of the coppery
solution, so that it will stand about an inch above the medal; then
pour in the glass the dilute acid to the same height as the former; now
introduce the zinc into the acid, and the object to be copied into the
solution of copper, which will immediately be deposited on the medal,
and when of a sufficient thickness may be taken off.




HEAT.


HEAT, OR CALORIC.

The chief agent in causing the repulsion or separation of the particles
of bodies from each other is heat, or more correctly _caloric_, by
which is understood the unknown _cause_ of the effect called heat.
Philosophers are not agreed upon the nature of this wonderful agent. It
pervades all nature, is the cause of nearly all the changes that take
place both in organic and inorganic matter, and has great influence in
the meteorological phenomena which we observe in the atmosphere that
surrounds our planet. It appears to be intimately connected with light,
electricity, and magnetism--subjects which the genius of Faraday and
others have investigated, and by their discoveries brought us nearer to
the knowledge of the real nature of these most wonderful forces.

Caloric, then, exists in all bodies, and has a constant tendency to
equalize itself, as far at least as its outward manifestation, called
temperature, is concerned; for if a _hot_ body be brought near colder
ones, it will give up heat to them, until by its loss and their gain
they all become of the same temperature; and this proceeds more or
less rapidly, according as the original difference of temperature
was greater or less. Some other circumstances also influence this
equalization. The converse will take place on introducing a cold body
among warmer ones, when heat will be abstracted from all the bodies
within reach of its influence, until it has absorbed sufficient caloric
to bring its own temperature to an equality with theirs. This is the
true explanation of the apparent production of _cold_. When, for
instance, an iceberg comes across a ship’s course, it appears to _give
out_ cold, whereas it has abstracted the heat from the air and sea in
its neighborhood, and they in turn act upon the ship and everything in
it, until one common temperature is produced in all the neighboring
bodies.

It does not follow that the bodies thus equalized in temperature
contain equal quantities of caloric; far from it. Each body requires
a particular quantity of caloric to raise its temperature through a
certain number of degrees; and such quantity is called its _specific_
caloric. A pound of water, for instance, will take just twice as much
caloric as a pound of olive oil, to raise its temperature through the
same number of degrees; the _specific_ caloric of water is therefore
double that of oil. Mix any quantity of oil at 60 deg. of temperature
with an equal weight of water at 90 deg., and you will find the
temperature of the mixture to be nearly 80 deg., instead of only 74
deg. or 75 deg., showing that while the water has lost only 10 deg.
of caloric, the mixture has risen 20 deg. If the oil be at 90 deg.,
and the water at 60 deg., the resulting temperature will be only 70
deg., or thereabouts, instead of 75 deg., the mean; thus, here the hot
oil has lost 20 deg., while the mixture has risen only 10 deg.; the
water, then, contains at the same temperature _twice_ as much caloric
as the oil; its specific caloric is _double_ that of the oil. This
mean temperature does result when equal weights of the same body at
different temperatures are mixed together.

The sensations called heat and cold are by no means accurate measures
of the real temperature of any substances, for many causes influence
these sensations, some belonging to the substances themselves, others
to the state of our organs at the time. Every one has remarked that
metals in a warm room feel warmer, and in a cold room colder than
wooden articles, and these again than woolen or cotton articles of
dress or furniture; this arises from metals being what is termed better
_conductors_ of heat than wood, and this better than wool, &c., that
is, they give out or absorb caloric more rapidly than these last. Some
philosophers, wishing to ascertain how much heat the human body could
endure, had a room heated with stoves, every crevice being carefully
stopped, until the temperature rose so high that a beefsteak placed
on the table was sufficiently cooked to be eaten. They were dressed
in flannel, and could with impunity touch the carpets, curtains,
&c., in the room; but the iron handles, fire-irons, and all metallic
substances, burnt their fingers; and one who wore silver spectacles was
obliged to remove them to save his nose. The fallacy of our sensations
may be easily shown by taking two basins, placing in one some water at
100 deg., in another some water at as low a temperature as can easily
be procured--hold the right hand in one, the left in the other, for a
few minutes, and then mix them, and place both hands in the mixture; it
will feel quite _cold_ to the hand that had been in the hotter water,
and _hot_ to the other.

In order to arrive at a correct estimate of the temperature of bodies,
instruments are made use of called thermometers, or measurers of
heat, which show increase or diminution of temperature by the rising
or falling of a column of some fluid in a tube of glass, one end of
which is expanded into a bulb, and the other hermetically sealed.
This effect is produced by the expansion or swelling of the fluid as
caloric is added to, and its contraction when caloric is abstracted
from it. Colored spirits of wine, or quicksilver, are the most usual
thermometric fluids, and the tube containing them is fixed to a wooden
or metallic frame, on which certain divisions are marked, called
degrees.

That in general use in America is called Fahrenheit’s from the name
of the person who first introduced that particular scale. In this
thermometer, the point at which the mercury in the tube stands when
plunged into melting ice, is marked 32 degrees, and the distance
between that point and the point to which the mercury rises in boiling
water is divided into 180 equal parts, called degrees; so that water is
said to boil at 212 degrees = 180 degrees + 32 degrees. There are two
other scales of temperature used in different parts of the world, but
it is not worth while to notice them here.

Not only do different bodies at the same degree of temperature contain
very different quantities of caloric, but this also is the case with
the same body in different forms. Ice, water, and steam are three forms
of the same body, but ice at 32 degrees contains much less caloric
than water at the same temperature, and water at 212 degrees contains
much less caloric than steam (or water in a state of vapor) at that
temperature.

Place in a jar any given quantity of snow, or small pieces of ice, at
32 degrees, and in another the same weight of water at 32 degrees, pour
on each an equal weight of water at 172 degrees, and you will find
that in the first case the ice will be melted, but the temperature
will remain at 32 degrees, or thereabouts, while the temperature
of the water in the other vessel will have risen to 100 degrees or
thereabouts, being as near as possible the half of the excess of the
temperature of the hot water, 140 degrees over that of the cold, namely
70 degrees added to 32 degrees, the original temperature. Now, what
has become of the heat which was added to the ice, and is apparently
lost?--it is _absorbed_ by the ice in its passage to the fluid state;
so that water may be said to be a compound of ice and caloric.

Again, take 10 ounces of water at about 50 degrees, and add 1 oz. of
water at 212 degrees, and the temperature of the mixture will be about
66 degrees; then condense some steam at 212 degrees into another 10 oz.
of water until it has become 11 oz., and you will find the temperature
will be nearly 212 degrees. Why does the ounce of steam at 212 degrees
raise the temperature of the water so much higher than the ounce of
water at the same temperature? Obviously because it contains hidden in
its substance a vast quantity of caloric, not to be detected by the
thermometer; in fact, that steam is a compound of _water_ and caloric,
as water is a compound of _ice_ and caloric; and this caloric which
exists, more or less, in all bodies without producing any obvious
effect, is called _latent_ caloric, from the Latin verb _lateo_, to
lie hid. The quantity of caloric thus absorbed, as it were, by various
bodies, differs for each body, and for the same body in different
forms, as mentioned above.


EXPANSION.

As a general rule, all bodies, whether solid, liquid, or gaseous, are
expanded by caloric. This may be shown by experiments in each form of
matter.

Have a small iron rod made, which when cold just passes through a hole
in a plate of metal; heat it, and it will no longer pass; after a time
the rod will return to its former temperature, and then will go through
the hole as before. The rod increases in length as well as width; if
you have a gauge divided into 1/100 of an inch, and place the rod in it
when cold, noting its position, on heating it will extend to a greater
length in the gauge, returning to its former place when cool.

The effect of caloric in causing fluids to expand is actually employed
as a measure of quantity in the thermometer, the rise of the fluid
in the tube when heated depending on the increased bulk of the fluid
occasioned by the addition of caloric. The same fact is to be noticed
every day when the cook fills the kettle, and places it on the fire. As
the water becomes warmer it expands, that is, takes up more room than
it did before, and the water escapes by slow degrees, increasing as the
heat increases, up to the point of boiling, when a sudden commotion
takes place from the condensation of a portion of the water into steam.

But it is in the form of vapor or gas (which, by the bye, is not the
same thing), that the expansive force of caloric is most obvious. The
gigantic powers of the steam-engine depend entirely on the tendency of
vapor to expand on the addition of caloric; and this force of expansion
appears to have no limit; boilers made of iron plates an inch or even
more in thickness, and the buildings or ships containing them, having
been torn to pieces and scattered in all directions by the expansive
power of steam. Take a bladder and fill it about half-full of air, and
tie the neck securely; upon holding it to the fire it will swell out
and become quite tense from the expansion of the contained air.

The principal source of caloric is the sun, whose beams, diffused
through all nature by the refractive property of the atmosphere,
are the source of vitality both to vegetables and animals, and when
concentrated by a large convex lens, produce the most intense heat,
sufficient to light a piece of diamond, and melt platinum. Caloric
is also produced or evolved by combustion, by friction, percussion,
chemical combination, electricity, and galvanism.

The evolution of heat by friction may be witnessed daily in a
thousand instances. Lucifer matches are lighted by rubbing the highly
inflammable substances with which they are tipped against a piece of
sand-paper. Nearly all savage people procure fire by rubbing a piece
of hard wood violently against a softer piece. The axle-trees of
steam-engines, and even of carriages, have been known to be so heated
by friction as to endanger burning the carriage; and it is very usual
to be obliged to pour a quantity of cold water on the iron axle of the
carriages of an express train after an hour of constant and rapid work.
If you merely rub the blade of a knife rapidly on a piece of wood it
will become hot enough to burn your hand.

Percussion is merely a more energetic kind of friction, and is often
resorted to by the blacksmith to light his furnace. He places a nail or
other piece of soft iron on his anvil, and beats it rapidly with the
hammer, when it becomes actually red hot. The production of sparks by
striking flint against steel, or two pieces of flint one against the
other, are familiar instances of heat produced by percussion.

One of the most powerful means of producing heat is the process of
combustion.

Combustion, as the word imports, is the _burning together_ of two or
more substances, a chemical union of oxygen generally with carbon
and hydrogen in some shape or other. In our ordinary fires we burn
coal, a hydro-carbon as it is called; and the gas which is now so
universally used for the purpose of illumination, is a compound of the
same bodies--so wax, tallow, oil of various kinds, both of animal and
vegetable origin, are all hydro-carbons.

On the application of a sufficient heat, and a free access of
atmospheric air, or of some other gas containing oxygen in a certain
state of combination, these bodies take fire, and continue to burn
either with flame, or a red or even white heat without flame,
until they are consumed; that is, until they have entered into new
combinations with the oxygen, and are converted into carbonic acid and
water, the carbon forming the first product, the hydrogen the other.

The following experiment shows the productions of heat by chemical
action alone. Bruise some fresh prepared crystals of nitrate of copper,
spread them over a piece of tin foil, sprinkle them with a little
water; then fold up the foil tightly as rapidly as possible, and in a
minute or two it will become red-hot, the tin apparently burning away.
The heat is produced by the energetic action of the tin on the nitrate
of copper, taking away its oxygen in order to unite with the nitrate
acid, for which, as well as for the oxygen, the tin has a much greater
affinity than the copper has.

Combustion without flame may be shown in a very elegant and agreeable
manner, by making a coil of platinum wire by twisting it round the stem
of a tobacco-pipe, or any cylindrical body, for a dozen times or so,
leaving about an inch straight, which should be inserted into the wick
of a spirit-lamp; light the lamp, and after it has burnt for a minute
or two extinguish the flame quickly; the wire will soon become red-hot,
and, if kept from draughts of air, will continue to burn until all the
spirit is consumed. Spongy platinum, as it is called, answers rather
better than wire, and has been employed in the formation of fumigators
for the drawing-room, in which, instead of pure spirits, some perfume,
such as lavender water, is used; by its combustion an agreeable odor is
diffused through the apartment. These little lamps were much in vogue a
few years ago, but are now nearly out of fashion.

Experiments on combustion might be multiplied almost to any amount, but
the above will be sufficient for the present. When we come to treat of
the properties of the gases and some other substances, we shall have
occasion to recur to this subject.

The production of caloric by chemical combination may be exhibited by
mixing carefully one part of oil of vitriol with two of water, when
sufficient heat will be produced to boil some water in a thin and
narrow tube, which may be used as a rod to stir the mixture.

The production of heat by electric and galvanic agency belongs to
another subject.




HYDRAULICS.


The science of Hydraulics comprehends the laws which regulate
non-elastic fluids in motion, and especially water, etc.

Water can only be set in motion by two causes--the pressure of the
atmosphere, or its own gravity. The principal law concerning fluids
is, that they always preserve their own level. Hence water can be
distributed over a town from any reservoir that is higher than the
houses to be supplied; and the same principle will enable us to
form fountains in a garden, or other place. Should any of our young
readers wish to form a fountain, they may, by bringing a pipe from a
water-tank, which should be at the upper part of the house, convey
the water down to the garden. Then, by leading it through the earth,
underneath the path or grass-plot, and turning it to a perpendicular
position, the water will spring out, and rise nearly as high as the
level of that in the tank. The pipe should have a faucet, so that the
water may be let on or shut off at pleasure.


THE SYPHON.

The syphon is a bent tube, having one leg shorter than the other. It
acts by the pressure of the atmosphere. In order to make a syphon
act, it is necessary first to fill both legs quite full of the fluid,
and then the shorter leg must be placed in the vessel to be emptied.
Immediately upon withdrawing the finger from the longer leg, the liquor
will flow.


THE PUMP.

The action of the common pump is as follows: When the handle is
raised, the piston-rod descends, and brings the piston-valve--called
the sucker, or bucket--to another valve, which is fixed, and opens
inward towards the piston. When the handle is drawn down, the piston
is raised, and, as it is air-tight, a vacuum is produced between the
two valves; the air in the barrel of the pump, betwixt the lower valve
and the water, then forces open the lower valve, and rushes through to
fill up this vacuum; and the air in the pump being less dense than the
external atmosphere, the water is forced a short way up the barrel.
When the piston again descends to the lower valve, the air between
them is again forced out by forcing open the upper valve; and when the
piston is raised, a vacuum is again produced, and the air below the
lower valve rushes up, and the water in consequence is again raised a
little further. This operation continues until the water rises above
the lower valve; at every stroke afterwards, the water passes through
the valve of the descending piston, and is raised by it, on its ascent,
until it issues out of the spout.


THE HYDRAULIC DANCER.

Make a little figure of cork, in the shape of a dancing mountebank,
sailor, etc. In this figure place a small hollow cone, made of thin
leaf brass. When this figure is placed upon any jet, such as that of
the fountain recommended to be constructed, it will be suspended on the
top of the water, and perform a great variety of amusing motions. If a
hollow ball of very thin copper, of an inch in diameter, be placed on a
similar jet, it will remain suspended, turning round and spreading the
water all about it.




MAGNETISM.


The attractive power of the loadstone has been known from a very
remote period. The natural magnet appears native in a gray iron ore
in octahedral crystals, composed of 168 parts of iron, and 64 parts
of oxygen. Its properties seem to have been studied in Europe during
the dark ages and a directive power is alluded to by Cardinal James de
Vitri, who flourished about the year 1200, who observed that it was
indispensable to those who travel much by sea.

In modern times, the history as well as the nature of the magnet has
engaged remarkable attention; and it has been determined beyond all
dispute that the magnet was used by the Chinese under the name of
the _tche-chy_ (directing stone) about 2604 years before Christ. It
passed from them to the Arabs, and was first used in Europe after the
crusades; and Ludi Vestomanus asserts that about the year 1500 he saw
a pilot in the East Indies direct his course by a magnetic needle like
those now in use.


TO MAKE ARTIFICIAL MAGNETS.

This may be done by stroking a piece of hard steel with a natural or
artificial magnet. Take a common sewing needle and pass the north pole
of a magnet from the eye to the point, pressing it gently in so doing.
After reaching the end of the needle the magnet must not be passed back
again towards the eye, but must be lifted up and applied again to that
end, the friction being always in the same direction. After repeating
this for a few times the needle will become magnetized, and attract
iron filings, etc.


HOW TO MAGNETIZE A POKER.

Hold it in the left hand in a position slightly inclined from the
perpendicular, the lower end pointing to the north, and then strike it
smartly several times with a large iron hammer, and it will be found
to possess the powers of a magnet, although but slightly.


TO SHOW MAGNETIC REPULSION AND ATTRACTION.

Suspend two short pieces of iron wire, so that they will hang in
contact in a vertical position. If the north pole of a magnet be now
brought to a moderate distance between the wires, they will recede from
each other.

The ends being made south poles by induction from the north pole, will
repel each other, and so will the north poles. This separation of the
wires will increase as the magnet approaches them, but there will be
a particular distance at which the attractive force overcomes the
repulsive force of the poles, and causes the wires to converge.


NORTH AND SOUTH POLES OF THE MAGNET.

Each magnet has its poles, north and south--the north or south poles
of one magnet repel the north and south pole of another. If a magnet
be dipped in some iron filings, they will be immediately attracted to
one end. Supposing this to be the north pole, each of the ends of the
filings, not in contact with the magnet, will become north poles, while
the ends in contact will by induction become south poles. Both will
have a tendency to repel each other, and the filings will stand on the
magnet.


POLARITY OF THE MAGNET.

The best method of proving this is to take a magnet or a piece of steel
rendered magnetic, and to place it on a piece of cork by laying it in
a groove cut to receive it. If the cork be placed in the center of a
basin of water, and allowed to swim freely on its surface, so that it
is not attracted by the sides of the basin, it will be found to turn
its north pole to the north, and its south pole to the south, the same
as the mariner’s compass. If you fix two magnets in two pieces of cork,
and place them also in a basin of water, and they are in a parallel
position with the same poles together, that is, north to north, and
south to south, they will mutually repel each other; but if the
contrary poles point to one another, as north to south, they will be
attracted.


THE MAGNETIC FISH.

Fish are to be purchased at the toy-stores, by which the young
“magnétique” may perform this experiment; they are made hollow, and
will float on the water. In the mouth of each should be inserted a
piece of magnetic wire. The angling rod is like any other rod, and has
a silken thread for a line, and an iron hook also strongly magnetized.
To catch the fish it is only necessary to put the hook in contact with
the noses of the fish, and they will be taken without any bait.


THE MAGNETIC SWAN.

The figure of a swan should be cut in cork, and within its beak a small
strongly magnetized piece of steel should be placed. The swan should
then be covered with a coating of white wax, and fashioned further into
the shape of a swan, and glass beads may be placed in its head for
eyes. This should be placed in a small tub or large basin of water, and
to make it swim about, you should place in a white stick about nine
inches long a magnetic bar, on which the north and south poles are
marked. If you wish to bring the swan towards you, present to him the
north pole of the wand, if you wish it to retire, present the south
pole, and thus you may direct the swan to any part you desire.


TO SUSPEND A NEEDLE IN THE AIR BY MAGNETISM.

Place a magnet on a stand to raise it a little above the table; then
bring a small sewing needle containing a thread, within a little of the
magnet, keeping hold of the thread to prevent the needle from attaching
itself to the magnet. The needle in endeavoring to fly to the magnet,
and being prevented by the thread, will remain curiously suspended in
the air, reminding us of the fable of Mahomed’s coffin.


TO MAKE ARTIFICIAL MAGNETS WITHOUT THE AID EITHER OF NATURAL LOADSTONES
OR ARTIFICIAL MAGNETS.

Take an iron poker and tongs, or two bars of iron, the larger and the
older the better, and fixing the poker upright, hold to it with the
left hand near the top by a silk thread, a bar of soft steel about
three inches long, one-fourth of an inch broad and one-twentieth
thick; mark one end, and let this end be downwards. Then grasping the
tongs with the right hand a little below the middle, and keeping them
nearly in a vertical line, let the bar be rubbed with the lower end of
the tongs, from the marked end of the bar to its upper end about ten
times of each side of it. By this means the bar will receive as much
magnetism as will enable it to lift a small key at the marked end; and
this end of the bar being suspended by its middle, or made to rest on
a joint, will turn to the north, and is called its north pole, the
unmarked end being the south pole. This is the method recommended by
Mr. Caxton, in his process, which he regarded superior to those in
former use, and of which a more detailed account will be found in his
interesting volume.


HORSE-SHOE MAGNETS.

The form of a horse-shoe is generally given to magnetized bars, when
both poles are wanted to act together, which frequently happens in
various experiments, such as for lifting weights by the force of
magnetic attraction, and for magnetizing steel bars by the process of
double touch, for which they are exceedingly convenient. The following
is the method of making a powerful magnetic battery of the horse-shoe
form. Twelve bars or plates of steel are to be taken, and having
been previously bent to the required form, that is, the horse-shoe
shape, they are then bound together by means of rivets at their ends;
before being finally fastened they are each separately magnetized and
afterwards finally united.

Horse-shoe magnets should have a short bar of soft iron adapted to
connect the two poles, and should never be laid by without such a piece
of iron adhering to them. Bar magnets should be kept in pairs with
their poles turned in contrary directions, and they should be kept from
rust. Both kinds of magnets have their power not only preserved but
increased, by keeping them surrounded with a mass of dry filings of
soft iron, each particle of which will re-act by its induced magnetism
upon the point of the magnet to which it adheres, and maintain in that
point its primitive magnetic state.


EXPERIMENT TO SHOW THAT SOFT IRON POSSESSES MAGNETIC PROPERTIES WHILE
IT REMAINS IN THE VICINITY OF A MAGNET.

Let a magnet and a key be held horizontally near one of its poles, or
near its lower edge. Then if another piece of iron, such as a small
nail, be applied to the other end of the key, the nail will hang
from the key, and will continue to do so while the magnet is slowly
withdrawn; but when it has been removed beyond a certain distance, the
nail will drop from the key, because the magnetism induced in the key
becomes at that distance too weak to support the weight of the nail.
That this is the real cause of its falling off may be proved by taking
a still lighter fragment of iron, such as a piece of very slender wire,
and applying it to the key. The magnetism of the key will still be
sufficiently strong to support the wire, though it cannot the nail,
and it will continue to support it even when the magnet is yet further
removed; at length, however, it drops off.


ELECTRO-MAGNETISM.

The identity of magnetism with electricity alluded to in a former
paragraph, has led to the formation of a new science under the above
name, and to some of the interesting experiments connected with it, we
shall briefly allude for the amusement of the young reader.


POWER OF THE ELECTRO-MAGNET.

The same influence which affects the magnetic needle already described,
will also communicate magnetism to soft iron. If a bar of that metal
bent, be surrounded with a common bonnet wire, or a copper wire
prevented from touching the iron by a winding of cotton or thread, and
then if a current of voltaic electricity be sent through the wire, the
bar becomes a powerful magnet, and will continue so as long as the
connection with the battery is preserved. On breaking the contact, the
magnetism disappears. This experiment may be easily made by the young
reader with a horse-shoe magnet, surrounded by several coils of wire.


THE MARINER’S COMPASS AND EXPERIMENTS WITH A POCKET COMPASS.

The mariner’s compass is an artificial magnet fitted in a proper
box, and consists of three parts--the box, the card or fly, and the
needle. The box is suspended in a square wooden case, by means of two
concentric brass circles called gimbals, so fixed by brazen axes to the
two boxes, that the inner one, or compass-box, retains a horizontal
position in all motions of the ship. The card is a circular piece of
paper which is fastened upon the needle, and moves with it. The outer
edge of the card is divided into thirty-two points, called points of
the compass. The needle is a slender bar of hardened steel, having a
hollow agate cup in the center, which moves upon the point of a pivot
made of brass.


VARIATION OF THE NEEDLE.

The magnetic needle does not point exactly north and south, but the
north pole of the needle takes a direction to the west of the true
north. It is constantly changing, and varies at different parts of the
earth, and at different times of the day.


DIP OF THE NEEDLE.

Another remarkable and evident manifestation of the influence of the
magnetism of the earth upon the needle is the inclination or dip of the
latter which is a deviation from its horizontal place in a downward
direction in northern regions of its north, and in southern regions of
its south pole. In balancing the needle on the card, on account of this
dipping, a small weight or movable piece of brass is placed on one end
of the needle, by the shifting of which either nearer to or further
from the center, the needle will always be balanced.


USEFUL AMUSEMENT WITH THE POCKET COMPASS.

Pocket compasses are to be bought for from 50 cents to $1, and may
be used in many ways. In traveling over mountains or a wide extended
plain, they are indispensably necessary, and no one should go on a tour
without such a companion; it will be a very useful and amusing exercise
for any young person to take the bearings of his own or some particular
locality, and make out what may be called a bearing card. This he may
easily do in the following manner: Supposing he wishes, for instance,
to take the bearings of his own house, he has nothing to do but set his
pocket compass upon a map of the district,--a county map will do very
well, unless his house stands on the verge of a county, then two county
maps will be necessary. He must make the north of the map exactly
coincide with the north, as indicated by his compass, and having fixed
his map in this situation, he should take a ruler and piece of paper,
and dot down the exact bearings of each important town, or place, or
village, around him. Let him suppose himself, for instance, in the town
of Albany, N. Y., and laying down his map as indicated by the compass,
north to north and south to south, he will find the following places
due north, Balston Spa; Hudson, south; Schoharie, west. The other
points of the compass may be filled up in the same manner. Should,
therefore, our young friend be upon any other elevated situation near
his own dwelling, or upon any other elevated spot from which the
bearings have been taken, he will be able to inform his young friends
that such and such a place lies in such a direction, that this place
lies due north, the other north-west, a third south-east, the fourth
south-west, etc., etc.


INTERESTING PARTICULARS CONCERNING THE MAGNET.

Fire-irons which have rested in an upright position in a room during
the summer months are often highly magnetic.

Iron bars standing erect, such as the gratings of a prison cell, or the
iron railings before houses, are often magnetic.

Great iron-clad ships are powerfully magnetic, and therefore affect
the compass by which the vessel is steered; ingenious arrangements are
therefore made to correct the effect of the local attraction, so that
the man-of-war may be steered correctly.

Magnetism may be made to pass through a deal board; to exhibit which,
lay a needle on the smooth part above, and run a magnet along the under
side, and the needle will be found to follow the course of the magnet.
A magnet dipped into boiling water loses part of its magnetism, which,
however, returns upon its cooling.

A sudden blow given to a magnet often destroys its magnetic power.




HOW TO BECOME A PHOTOGRAPHER.


Associated with the use of iodine and bromine is an art which every
intelligent boy may practice, if he will attend to the following
precise details kindly furnished by an experienced photographer.


HOW TO MAKE THE NEGATIVE ON GLASS, USING COLLODION BROMOIODIZED FOR
IRON DEVELOPMENT.

1. The edges of the glass should be ground all round, also slightly
on the surface of the edges. This prevents contraction of the film,
enabling it to resist the action of a heavy stream of water. Mark
one side in the corner with a diamond, and upon this side bestow the
greatest care.

2. _To clean the glass, if new._--Make a mixture of spirits of wine
and solution of ammonia, equal parts; render it as thick as cream with
tripoli; with a piece of cotton-wool kept for this purpose rub a small
quantity over that side marked as described, wash well under a tap of
water, and wipe dry with a piece of old linen, washed without soap, and
kept scrupulously clean for this purpose. Plates should not, however,
be cleaned in the operating room with the above mixture; the vapor of
ammonia might prove injurious to the chemicals.

3. Now polish with an old white silk handkerchief. If this latter
precaution be not taken, small particles of linen will be left upon the
plate: these are perhaps only seen when draining off the collodion;
they form nuclei and eddies, checking the collodion in its course.
Some of these minute fibers are washed off, and contaminate the next
picture. To all lovers of clean pictures our advice therefore is,
having well dried the plate with old linen, lay it, clean side upwards,
upon a few sheets of common glazed demy paper (not blotting), and
rub it hard with the silk until sensibly warm; this has the double
advantage of dispersing fibers and moisture, for all glass plates are
slightly in a hygrometric condition. Double the silk rubber up to form
a pad, and with this the glass must be firmly dusted down just before
pouring on the collodion, which will then run most evenly; if the
coated plate is now viewed by transmitted light, not a speck or blemish
will be seen upon it. When a plate cleaned as above described is
breathed upon, the moisture does not evaporate slowly, but _flies off_.
Do not be afraid of putting the glass into an electrical condition with
the silk rubber; on this account objections have been raised to the use
of silk; practically, however, I find it a most valuable auxiliary in
this starting-point of the process, the perfect manipulation of which
makes an important difference in the value of the finished picture.
What can be more inartistic and annoying to an educated eye than spots,
patches, stars, and sky-rockets, the forms and shapes of which rival,
in numberless variety, a display of fireworks? Let us not, therefore,
be contented with pictures, however good in other respects, presenting
these deformities--so many blots on the photographic escutcheon.

_To clean a glass after having used it, when not varnished._--Wash off
the collodion film with water, then clean the marked side with plain
tripoli and water, and dry as above.

_To coat the plate._--First remove all the particles of dried collodion
from the mouth of the bottle. Now pour upon the center of the cleaned
glass as much collodion as it will hold. Do not perform this operation
hurriedly, take time, and systematically incline the plate in such a
manner that the collodion may run into each corner in succession; when
perfectly covered, pour off gently the excess into the bottle at one of
the corners nearest to you; with observation and practice dexterity is
easily acquired. There are many ways of coating the plate; each person
will adopt that which practice teaches him is best. The pneumatic
plate-holder is a convenient little instrument to use for holding the
plate whilst pouring on the collodion; it may be used for both small
and large plates.

Keep the corner of the glass plate in contact with the neck of the
bottle whilst pouring off the collodion; otherwise the film will be
wavy in places.

4. As soon as the collodion ceases to run, plunge the prepared glass
gently, without stopping, into the nitrate of silver bath, which is
prepared as follows: Into a 20-oz. stoppered bottle put nitrate of
silver, 1-1/4 ozs.; distilled water, 4 ozs.; dissolve. To this solution
add iodide of potassium, 4 grs., dissolved in one drachm of distilled
water. Mix these two solutions; the precipitate (iodide of silver)
thus formed is by shaking entirely dissolved. Add 16 ozs. of distilled
water, when the excess of iodide of silver is again thrown down, but
in such a finely divided state as to render the saturation of the bath
with iodide of silver perfect. Now drop in sufficient of the oxide of
silver to turn the turbid yellow solution a dirty brown color; so long
as this effect is produced the quantity of oxide of silver, however
much in excess, is of no consequence; shake the bottle well for ten
minutes or so at intervals; then add alcohol, 30 minims, and filter; to
the filtered solution add dilute nitric acid of the strength stated, 5
minims. The bath is now ready for use, and should be quite neutral.

5. Allow the prepared glass to remain in this bath from five to ten
minutes, according to the temperature. Move it up and down three or
four times whilst in the bath, in order to get rid of the greasy
appearance on the surface; drain it, but not too closely. When in the
frame, place upon the back a piece of common blotting-paper, to absorb
moisture, and the two lower silver wires should also be covered with
slips of blotting-paper; after which the sooner it is placed in the
camera the better.

6. The time of exposure can only be ascertained by practice--no rules
can be laid down; and I am unacquainted with any royal road, but that
of experience, leading to constant success in this most important point.

7. The plate having been taken from the camera and placed upon a
leveled stand, or held in the hand, develop immediately the latent
image with the following solution:

_Iron developing solution._--Protosulphate of iron, 1/4 oz.; glacial
acetic acid, 1/4 oz.; spirits of wine, 1/2 oz.; distilled water, 8
ozs.; mix. Pour on of this solution only enough to cover the plate
easily, commencing at that edge of the negative which stood uppermost
in the camera; move the solution to and fro until it has become
intimately mixed with the silver on the plate; then pour off into the
developing glass, and _at once_ return it on to the plate. When as much
intensity has been obtained as possible with the iron developer, it
should be thoroughly removed by washing with water. Any intensity may
be obtained afterwards by using either of the following solutions:

8. _Intensifying solution._--Pyrogallic acid, 6 grs.; glacial acetic
acid, 1/4 oz.; distilled water, 6 ozs.; mix. A few drops of a 30-gr.
solution of nitrate of silver, the quantity to be regulated according
to the intensity required, to be added, at the moment of using, to as
much of the pyrogallic solution as may be necessary.

_Intensifying solution_ (another form).--1. Pyrogallic acid, 8 grs.;
citric acid, 20 grs.; distilled water, 2 ozs. 2. Nitrate of silver, 8
grs.; distilled water, 2 ozs. Mix small quantities of the solutions 1
and 2, in equal portions, the moment before using.

The pyrogallic solution, made with good acetic acid, may be kept for
a month or more in a cool place. Nevertheless, if the conditions of
light and situation are unfavorable, I should prefer this solution just
made. The iron solutions act best when freshly prepared.

It is supposed by some that a prolonged action of the iron developer
produces fogginess. This may be the case when impure or improperly
prepared collodion is used, but certainly not when the preparation is
pure and of the proper quality.

When the image is sufficiently intense, wash freely with common
filtered water; then pour on a saturated solution of hyposulphate of
soda, which should immediately remove the iodide of silver: wash again
well with water; allow as much as the plate will hold to soak in for
at least a quarter of an hour, changing the water occasionally, to
remove all traces of hyposulphate; lastly, wash the plate with a little
distilled water, stand up to dry, and, if required, varnish either with
spirit or amber varnish.

The following solution is also very commonly used for fixing the
negative:--Cyanide of potassium, 1/4 oz.; water, 12 ozs.

Attention to the following rules and cautions will assist the operator
in the production of perfect pictures:--

1. Do not disturb the deposit which will occasionally be found at the
bottom of the bottle containing the collodion.

2. Remove all particles of dried film from the neck of the bottle
before pouring the collodion on the plate.

3. Never use damp cloths, leathers, or buffs, for giving the final
polish to the plate. Negatives with an indistinct and muddy surface are
frequently produced from this cause.

4. Let the film set properly before immersion in the nitrate of silver
bath: its condition can be ascertained by gently touching the lower
part of the coated plate with the end of the finger.

5. Never omit to pass a broad camel-hair brush over the plate just
before pouring on the collodion.

6. Bear in mind that, as light is the producing agent, so will it prove
a destructive one: not less than four folds of yellow calico should be
used to obstruct white light; and in that case the aperture covered
should be no larger than is necessary to admit sufficient light for
working by. Examine occasionally the yellow calico: when this material
is used to exclude white light, it becomes bleached by constant
exposure. Do not trust alone to any colored glass; no glass yet made is
anti-actinic under all aspects of light and conditions of exposure.

7. When the negative requires intensifying, carefully wash off
all traces of the first developing solution before proceeding to
intensify. This operation may be performed either before or after the
iodide is removed by fixing.

8. Glass baths are preferable to porcelain, ebonite, or gutta-percha
baths for solution of nitrate of silver.

9. In using either spirit or amber varnish, before pouring it off, keep
the plate horizontal a few seconds. This gives time for soaking in,
and prevents the formation of a dull surface arising from too thin a
coating.

10. Rub the lenses occasionally with a soft and clean wash-leather, the
rapidity of action is much influenced by the brightness of the lenses:
their surfaces are constantly affected by moisture in the atmosphere,
which condensing, destroys the brilliancy of the image.

11. The white blotting-paper used for some photographic purposes is not
suitable for filtering solutions; that only should be employed which is
made for this purpose, and is sold under the name of filtering-paper.

12. _Hyposulphate of soda._--A great deal of rubbish is sold under
the name of this salt. As a test of its quality, 1-1/2 drachms should
entirely dissolve in 1 drachm of water, and this solution should
dissolve rather more than 4-1/2 grains of iodide of silver.

13. _Chemicals._--The purity of photographic chemicals cannot be too
strongly urged; the cheapest are not always the most economical.
The commercial preparations are generally not to be depended upon,
as these, though perhaps unadulterated, are, strictly speaking, not
chemically pure. It is best to procure them from well-known chemists,
who understand the purpose for which they are intended, and make the
preparation of these substances peculiarly a branch of their business.

14. Never leave chemical solutions exposed in dishes: when done with,
pour them back into glass-stoppered bottles, and decant for use from
any deposit, or filter if necessary.

15. In all photographic processes it is absolutely necessary to be
chemically clean; and this sometimes is not easy. As a rule, never be
satisfied with cleanly appearances only, but take such measures as
shall insure the absence of all extraneous matter in preparing the
solutions, cleaning the glasses, dishes, etc.

16. All stains on the hands, linen, etc., may be removed by means of
cyanogen soap or cyanide of potassium, which should be applied without
water at first, then thoroughly washed off. To assist the operation,
the hands may be now gently rubbed with a fine piece of pumice-stone,
when the stains quickly disappear.

For more perfect and complete directions, the reader is referred to any
complete work on photography.




MECHANICS.


There is no subject of such importance as Mechanics, as its principles
are founded upon the properties of matter and the laws of motion; and
in knowing something of these, the tyro will lay the foundation of all
substantial knowledge.

The properties of matter are the following: Solidity (or
Impenetrability), Divisibility, Mobility, Elasticity, Brittleness,
Malleability, Ductility, and Tenacity.

The laws of motion are as follows:--

1. Every body continues in a state of rest or of uniform rectilineal
motion, unless affected by some extraneous force.

2. The change of motion is always proportionate to the impelling force.

3. Action and reaction are always equal and contrary.


EXPERIMENT OF THE LAW OF MOTION.

In shooting at “taw,” if the marble be struck “plump,” as it is called,
it moves forward exactly in the same line of direction; but if struck
sideways, it will move in an oblique direction, and its course will be
in a line situated between the direction of its former motion and that
of the force impressed. This is called the resolution of forces.


BALANCING.

The center of gravity in a body is that part about which all the other
parts equally balance each other. In balancing a stick upon the finger,
or upon the chin, it is necessary only to keep the chin or finger
exactly under the point which is called the center of gravity.


THE PRANCING HORSE.

Cut out the figure of a horse, and having fixed a curved iron wire to
the under part of its body, place a small ball of lead upon it. Place
the hind legs of the horse on the table, and it will rock to and fro.
If the ball be removed, the horse would immediately tumble, because
unsupported, the center of gravity being in the front of the prop;
but upon the ball being replaced, the center of gravity immediately
changes as position, and is brought under the prop, and the horse is
again in equilibrio.


TO CONSTRUCT A FIGURE, WHICH BEING PLACED UPON A CURVED SURFACE, AND
INCLINED IN ANY POSITION, SHALL, WHEN LEFT TO ITSELF, RETURN TO ITS
FORMER POSITION.

The feet of the figure rest on a curved pivot, which is sustained
by two loaded balls below; for the weight of these balls being much
greater than that of the figure, their effect is to bring the center of
gravity of the whole beneath the point on which it rests; consequently
the equilibrium will resist any slight force to disturb it.


TO MAKE A CARRIAGE RUN IN AN INVERTED POSITION WITHOUT FALLING.

It is pretty well known to most boys, that if a tumbler of water be
placed within a broad wooden hoop, the whole may be whirled round
without falling, owing to the centrifugal force. On the same principle,
if a small carriage be placed on an iron band or rail, it will ascend
the curve, become inverted, and descend again, without falling.


TO CAUSE A CYLINDER TO ROLL BY ITS OWN WEIGHT UP-HILL.

Procure a coffee-canister, and loading it with a piece of lead, which
may be fixed in with solder, the position of the center of gravity is
thus altered. If a cylinder so constructed be placed on an inclined
plane, and the loaded part above, it will roll up-hill without
assistance.


THE BALANCED STICK.

Procure a piece of wood, about nine inches in length, and about half
an inch in thickness, and thrust into its upper end the blades of two
pen-knives, on either side one. Place the other end upon the tip of the
fore-finger, and it will keep its place without falling.


THE CHINESE MANDARIN.

Construct out of the pith of the elder a little mandarin; then provide
a base for it to sit in, like a kettle drum. Into this put some heavy
substance, such as half a leaden bullet; fasten the figure to this, and
in whatever position it may be placed, it will, when left to itself,
immediately return to its upright position.


TO MAKE A SHILLING TURN ON ITS EDGE ON THE POINT OF A NEEDLE.

Take a bottle, with a cork in its neck, and place in it, in a
perpendicular position, a middle-sized needle. Fix a shilling into
another cork, by cutting a nick in it; and stick into the same cork
two small table-forks, opposite each other, with the handles inclining
outwards and downwards. If the rim of the shilling be now poised on
the point of the needle, it may easily be made to spin round without
falling, as the center of gravity is below the center of suspension.


THE DANCING PEA.

If you stick through a pea, or small ball of pith, two pins at right
angles and defend the points with pieces of sealing-wax, it may be kept
in equilibrio at a short distance from the end of a straight tube, by
means of a current of breath from the mouth, which imparts a rotary
motion to the pea.


OBLIQUITY OF MOTION.

Cut a piece of pasteboard into a circular shape, and describe on it a
spiral line; cut this out with a pen-knife, and then suspend it on a
large skewer or pin. If the whole be now placed on a warm stove, or
over the flame of a candle or lamp, it will revolve with considerable
velocity. The card, after being cut into the spiral, may be made to
represent a snake or dragon, and when in motion will produce a very
pleasing effect.




PNEUMATICS.


The branch of the physical sciences which relates to the air and its
various phenomena is called Pneumatics. By it we learn many curious
particulars. By it we find that the air has weight and pressure,
color, density, elasticity, compressibility, and some other properties
with which we shall endeavor to make the young reader acquainted by
many pleasing experiments, earnestly impressing upon him to lose no
opportunity of making physical science his study.

The common leather sucker by which boys raise stones will show the
pressure of the atmosphere. It consists of a piece of soft but firm
leather having a piece of string drawn through its center. The leather
is made quite wet and pliable, and then its under part is placed on the
stone and stamped down by the foot. This pressing excludes the air from
between the leather and the stone, and by pulling the string a vacuum
is left underneath its center; consequently the leather is firmly
attached to the stone, which enables you to lift it.


WEIGHT OF THE AIR PROVED BY A PAIR OF BELLOWS.

Shut the nozzle and valve-hole of a pair of bellows, and after having
squeezed the air out of them, if they are perfectly air-tight, we
shall find that a very great force, even some hundreds of pounds, is
necessary for separating the boards. They are kept together by the
weight of the air which surrounds them in the same manner as if they
were surrounded by water.


THE PRESSURE OF THE AIR SHOWN BY A WINE-GLASS.

Place a card on a wine-glass filled with water, then invert the glass;
the water will not escape, the pressure of the atmosphere on the
outside of the card being sufficient to support the water.


ANOTHER.

Invert a tall glass jar in a dish of water, and place a lighted taper
under it; as the taper consumes the air in the jar, the water, from
the pressure without, _rises up_ to supply the place of the oxygen
removed by the combustion. In the operation of cupping the operator
holds the flame of a lamp under a bell-shaped glass. The air within
this being rarefied and expanded, a considerable portion is given
off. In this state the glass is placed upon the flesh, and as the air
within it cools it contracts, and the glass adheres to the flesh by the
difference of the pressure of the internal and external air.


ELASTICITY OF THE AIR.

This can be shown by a beautiful philosophical toy, which may easily be
constructed. Procure a glass jar and put water into it. Then mold three
or four little figures in wax, and make them hollow within, and having
each a minute opening at the heel, by which water may pass in and
out. Place them in the jar, and adjust them by the quantity of water
admitted to them, so that in specific gravity they differ a little from
each other. The mouth of the jar should now be covered with a piece of
skin or india-rubber, and then, if the hand be pressed upon the top
or mouth of the jar, the figures will be seen to rise or descend as
the pressure is gentle or heavy; rising and falling or standing still,
according to the pressure made.


REASON FOR THIS.

The reason of this is, that the pressure on the top of the jar
condenses the air between the cover and the water surface; this
condensation then presses on the water below, and influences it through
its whole extent, compressing also the air in the figures, forcing as
much more water into them as to render them heavier than water, and
therefore heavy enough to sink.


THE AIR-PUMP.

The time was, and that not very long ago, when the air-pump was only
obtainable by the philosophical professor or by persons of enlarged
means. But now, owing to our “cheap way of doing things,” a small
air-pump may be obtained for about $5, and we would strongly advise
our young friends to procure one, as it will be a source of endless
amusement to them; and, supposing that they take our advice, we suggest
the following experiments.

The air-pump consists of a bell glass, called the receiver, and a stand
upon which is a perforated plate. The hole in this plate is connected
with two pistons, the rods of which are moved by a wheel handle
backwards and forwards, and thus pumps the air out of the receiver.
When the air is thus taken out, a stop-cock is turned, and then the
experiments may be performed.

Under the receiver of an air-pump, when the air has been thoroughly
exhausted, light and heavy bodies fall with the same swiftness. Animals
quickly die for want of air, combustion ceases, a bell sounds faint,
and water and other fluids change to vapor.


TO PROVE THAT AIR HAS WEIGHT.

Take a florence flask, fitted up with a screw and fine oiled silk
valve. Screw the flask on the plate of the air-pump, exhaust the air,
take it off the plate, and weigh it. Then let in the air, and again
weigh the whole, and it will be found to have increased by several
grains.


TO PROVE AIR ELASTIC.

Place a bladder out of which all the air has apparently been squeezed
under the receiver, upon it lay a weight, exhaust the air, and it will
be seen that the small quantity of air left within the bladder will
so expand itself as to lift the weight. Put a corked bottle into the
receiver, exhaust the air, and the cork will fly out.


SOVEREIGN AND FEATHER.

Place a nicely-adjusted pair of forceps at the top of the receiver,
communicating with the top of the outside through a hole, so that they
may be opened by the fingers. Then place on each of the little plates
a _sovereign_ and a _feather_. Exhaust the air from the receiver: and
having done so, detach the objects, so that they may fall. In the open
air the sovereign will fall long before the feather, but in vacuo, as
in the receiver now exhausted of its air, they will fall both together,
and reach the bottom of the glass at the same instant.


AIR IN THE EGG.

Take a fresh egg, and cut off a little of the shell and film from
its smaller end; then put the egg under a receiver, and pump out the
air; upon which all the contents of the egg will be forced out by the
expansion of the small bubble of air contained in the great end between
the shell and the film.


THE DESCENDING SMOKE.

Set a lighted candle on the plate, and cover it with a tall receiver.
The candle will continue to burn while the air remains, but when
exhausted, will go out, and the smoke from the wick, instead of rising,
will descend in dense clouds towards the bottom of the glass, because
the air which would have supported it has been withdrawn.


THE SOUNDLESS BELL.

Set a bell on the pump-plate, having a contrivance so as to ring it at
pleasure, and cover it with a receiver; then make the clapper sound
against the bell, and it will be heard to sound very well; now exhaust
the receiver of air, and then when the clapper strikes against the
sides of the bell the sound can be scarcely heard.


THE FLOATING FISH.

If a glass vessel containing water, in which a couple of fish are put,
be placed under the receiver, upon exhausting the air the fish will be
unable to keep at the bottom of the glass owing to the expansion of
the air within their bodies, contained in the air bladder. They will
consequently rise and float, belly upwards, upon the surface of the
water.


THE DIVING BELL.

The diving bell is a pneumatic engine, by means of which persons can
descend to great depths in the sea, and recover from it valuable
portions of wrecks and other things. Its principle may be well
illustrated by the following experiment. Take a glass tumbler, and
plunge it into the water with the mouth downwards, and it will be
found that the water will not rise much more than half way in the
tumbler. This may be made very evident if a piece of cork be suffered
to float inside the glass on the surface of the water. The air
within the tumbler does not entirely exclude the water, because air
is elastic, and consequently compressible, and hence the air in the
tumbler is what is called condensed. The diving bell is formed upon the
above principle; but instead of being glass it is a wooden or metal
vessel, of very large dimensions, so as to hold three or four persons,
who are supplied with air from above by means of powerful pumps, whilst
the excess of air escapes at the bottom of the bell.


EXPERIMENTS.

1. Place a cylinder of strong glass, open at both ends, on the plate
of the air-pump, and put your hand on the other end, and you will of
course be able to remove it at pleasure. Now exhaust the air from the
interior of the cylinder, and at each stroke of the pump you will feel
your hand pressed tighter and tighter on the cylinder, until you will
not be able to remove it: as soon as the air is again admitted to the
interior of the cylinder, the pressure within will be restored, and the
hand again be at liberty.

2. Tie a piece of moistened bladder very firmly over one end of a
similar glass cylinder, and place the open end on the plate of the
pump. As soon as you begin to exhaust the air from the interior, the
bladder, which was previously quite horizontal, will begin to bulge
inwards, the concavity increasing as the exhaustion proceeds, until the
bladder, no longer able to bear the weight of the superincumbent air,
breaks with a loud report.

3. The elasticity of air, or indeed of any gaseous body, may be shown
by introducing under the air-pump receiver a bladder containing a very
small quantity of air, its mouth being closely tied. As you exhaust
the air from the receiver, that portion contained in the bladder being
no longer pressed upon by the atmosphere, will gradually expand,
distending the bladder until it appears nearly full: on readmitting the
air into the receiver, the bladder will at once shrink to its former
dimensions.

A shriveled apple placed under the same conditions will appear plump
when the air is removed from the receiver, and resume its former
appearance on the readmission of the air.

4. There is a very pretty apparatus made for the purpose of showing
the pressure of the atmosphere, consisting of a hollow globe of brass,
about three inches in diameter, divided into two equal parts, which
fit very accurately together. It is furnished with two handles; one of
them screwed into a hollow stem, communicating with the interior of the
globe, and fitting on to the air-pump; the other is attached to a short
stem on the opposite side of the globe. In the natural state the globe
may easily be separated into its two hemispheres by one person pulling
the handles, but after the air has been exhausted from the interior it
requires two very strong men to separate the parts, and they will often
fail to do so. By turning the stop-cock, and readmitting the air into
the interior of the globe, it will come asunder as easily as at first.

We are indebted to the weight of the atmosphere for the power we
possess of raising water by the common pump; for the piston of the pump
withdrawing the air from the interior of the pipe, which terminates in
water, the pressure of the atmosphere forces the water up the pipe to
supply the place of the air withdrawn. It was soon found, however, that
when the column of water in the pipe was more than thirty feet high,
the pump became useless, for the water refused to rise higher. Why?
It was found that a column of water about thirty feet high exerted a
pressure equal to the weight of the atmosphere, thus establishing an
equilibrium between the water in the pipe and the atmospheric pressure.

This is the principle on which the barometer, or _measurer of weight_,
as its name imports, is constructed. The metal Mercury is about
thirteen and a half times heavier than water; consequently, if a column
of water thirty _feet_ high balances the pressure of the atmosphere, a
column of mercury thirty _inches_ high ought to do also--and this is
in fact the case. If you take a glass tube nearly three feet long, and
closed at one end, and fill it with mercury; then, placing your finger
on the open end, invert the tube into a basin or saucer containing
some of the same metal; upon removing your finger (which must be
done carefully, while the mouth of the tube is completely covered by
the mercury), it will be seen that the fluid will fall a few inches,
leaving the upper part of the tube empty. Such a tube with a graduated
scale attached is in truth a barometer, and as the weight of the
atmosphere increases or decreases, so the mercury rises or falls in
the tube. This instrument is of the greatest value to the seaman, for
a sudden fall of the barometer will often give notice of an impending
storm when all is fine and calm, and thus enable the mariner to make
the preparations necessary to meet the danger.

It was discovered by an Italian philosopher named Torricelli, and from
him the vacuum formed in the upper end of the tube above the surface
of the mercury has been called the Torricellian vacuum. It is by far
the most perfect vacuum that can be obtained, containing necessarily
nothing but a minute quantity of the vapor of mercury.


EXPERIMENT.

Pass a little ether through the mercury in the tube, and as soon as
it reaches the empty space it will boil violently, depressing the
mercury, until the pressure of its own vapor is sufficient to prevent
its ebullition. If you now cool the upper part of the tube, so as to
condense the vapor, the pressure being thus removed, the ether will
again begin to boil, and so alternately, as often as you please. In
order to show this fact with effect, the bore of the tube should not be
less than half an inch in diameter.


EXPERIMENT.

To show that the heat abstracted by the boiling of one liquid will
freeze another, fill a tall narrow glass about half full of cold water
(the colder the better), and place in it a thin glass tube containing
some ether. Put them under the receiver of an air-pump. As you exhaust
the air, the ether will begin to boil, until at length, by continuing
the exhaustion, the water immediately surrounding the tube of ether
will freeze, and a tolerably large piece of ice may thus be obtained.

Ether evaporates so rapidly even under the pressure of the atmosphere,
that a small animal, such as a mouse, may be actually frozen to
death by constantly dropping ether upon it. If poured on the hand,
it produces a degree of cold that soon becomes, to say the least,
unpleasant.


EXPERIMENT.

Place a flat saucer containing about a pound of oil of vitriol under
the receiver of the air-pump, and set in it a watch glass containing
a little water, supported on a stand with _glass_ legs. Exhaust the
receiver, when the water will evaporate, but without boiling; and the
vapor being absorbed as it forms by the oil of vitriol, the vacuum
is preserved, and the evaporation continues, until the vapor has
abstracted so much caloric from the remainder of the water that it is
all at once converted into ice.

In most elementary works on chemistry may be found a long table of
freezing mixtures, as they are called, some with and others without
ice or snow. We have selected a few from each division.


WITH ICE OR SNOW.

  {Snow or powdered ice          2 parts.
  {Powdered common salt          1   “

  {Snow                          5   “
  {Powdered common salt          2   “
  {Powdered sal ammoniac         1   “

  {Snow                          3   “
  {Dilute sulphuric acid         2   “

  {Snow                          2   “
  {Crystallized muriate of lime  3   “


WITHOUT SNOW OR ICE.

  {Sulphate of soda    3 parts.
  {Dilute nitric acid  2   “

  {Nitrate of ammonia  1   “
  {Water               1   “

  {Phosphate of soda   2   “
  {Dilute nitric acid  1   “

  {Sulphate of soda    2   “
  {Muriatic acid       1   “

The effects of most of these mixtures may be considerably increased
by previously cooling the ingredients _separately_ in other freezing
mixtures.

In connection with this branch of science, and especially with
chemistry, the youthful philosopher should practice the art of
decanting air from one jar to another standing over water, beginning
by passing it from a small to a larger jar, then with two of equal
size; and when he can accomplish the transfer without permitting even
one bubble to escape, he may essay the much more difficult task of
transferring the air from a large to a smaller jar.

He should also practice using the blowpipe until he can keep up a
steady and uninterrupted flame for ten minutes or a quarter of an hour,
without stopping for breath. It is quite possible to replenish _wind_
in the mouth, which alone ought to be used, without interrupting the
breathing for an instant, but it requires some practice.




HOW TO BECOME AN OPTICIAN.


Optics is the science of _light_ and _vision_. Concerning the nature
of light, two theories are at present very ably maintained by their
respective advocates. One is termed the Newtonian theory, and the
other the Huygenean. The Newtonian theory considers light to consist
of inconceivably small bodies emanating from the sun, or any other
luminous body. The Huygenean conceives it to consist in the undulations
of a highly elastic and subtle fluid, propagated round luminous centers
in spherical waves, like those arising in a placid lake when a stone is
dropped into the water.


LIGHT AS AN EFFECT.

Light follows the same laws as gravity, and its intensity or degree
decreases as the square of the distance from the luminous body
increases. Thus, at the distance of two yards from a candle we shall
have four times less light than we should have were we only one yard
from it, and so on in the same proportion.


REFRACTION.

Bodies which suffer the rays of light to pass through them, such as
air, water, or glass, are called refracting media. When rays of light
enter these, they do not proceed in straight lines, but are said
to be refracted, or bent out of their course. But if the ray falls
perpendicularly on the glass, there is no refraction, and it proceeds
in a direct line; hence, refraction only takes place when rays fall
obliquely or aslant on the media.


THE INVISIBLE COIN MADE VISIBLE.

If a coin be placed in a basin, so that on standing at a certain
distance it be just hid from the eye of an observer by the rim or edge
of the basin, and then water be poured in by a second person, the first
keeping his position; as the water rises the coin will become visible,
and will appear to have moved from the side to the middle of the basin.


THE MULTIPLYING GLASS.

The multiplying glass is a semicircular piece of glass cut into facets
or distinct surfaces; and in looking through it we have an illustration
of the laws of refraction, for if a small object, such as a fly, be
placed at the further end, a person will see as many flies as there are
surfaces or facets on the glass.


TRANSPARENT BODIES.

Transparent bodies, such as glass, may be made of such form as to
cause all the rays which pass through them from any given point to
meet in any other given point beyond them, or which will disperse them
from the given point. These are called lenses, and have different
names according to their form. 1. Is called the plano-convex lens. 2.
Plano-concave. 3. Double convex. 4. Double concave. 5. A meniscus, so
called from its resembling the crescent moon.


THE PRISM.

The prism is a triangular solid of glass, and by it the young optician
may decompose a ray of light into its primitive and supplementary
colors, for a ray of light is of a compound nature. By the prism the
ray is divided into its three primitive colors, blue, red, and yellow;
and their four supplementary ones, violet, indigo, green, and orange.
The best way to perform this experiment is to cut a small slit in a
window-shutter, on which the sun shines at some period of the day, and
directly opposite the hole place a prism; a beam of light in passing
through it will then be decomposed, and if let fall upon a sheet of
white paper, or against a white wall, the seven colors of the rainbow
will be observed.


COMPOSITION OF LIGHT.

The beam of light passing through the prism is decomposed, and the
spaces occupied by the colors are in the following proportions: Red, 6;
orange, 4; yellow, 7; green, 8; blue, 8; indigo, 6; violet, 11. Now,
if you paste a sheet of white paper on a circular piece of board about
six inches in diameter, and divide it with a pencil into fifty parts,
and paint colors in them in the proportions given above, painting them
dark in the center parts, and gradually fainter at the edges, till they
blend with the one adjoining. If the board be then fixed to an axle,
and made to revolve quickly, the colors will no longer appear separate
and distinct, but becoming gradually less visible they will ultimately
appear _white_, giving this appearance to the whole surface of the
paper.


A NATURAL CAMERA OBSCURA.

The human eye is a camera obscura, for on the back of it on the retina
every object in a landscape is beautifully depicted in miniature. This
may be proved by the


BULLOCK’S EYE EXPERIMENT.

Procure a fresh bullock’s eye from the butcher, and carefully thin the
outer coat of it behind: take care not to cut it, for if this should
be done the vitreous humor will escape, and the experiment cannot be
performed. Having so prepared the eye, if the pupil of it be directed
to any bright objects, they will appear distinctly delineated on the
back part precisely as objects appear in the instrument we are about to
describe. The effect will be heightened if the eye is viewed in a dark
room with a small hole in the shutter, but in every case the appearance
will be very striking.


THE CAMERA OBSCURA.

This is a very pleasing and instructive optical apparatus, and it may
be easily made by the young optician. Procure an oblong box, about two
feet long, twelve inches wide, and eight high. In one end of this a
tube must be fitted containing a lens, and be made to slide backwards
and forwards so as to suit the focus. Within the box should be a plain
mirror reclining backwards from the tube at an angle of forty-five
degrees. At the top of the box is a square of unpolished glass, upon
which from beneath the picture will be thrown, and may be seen by
raising the lid. To use the camera place the tube with the lens on it
opposite to the object, and having adjusted the focus, the image will
be thrown upon the ground-glass as above stated, where it may be easily
copied by a pencil or in colors.

The camera obscura used in a public exhibition is a large wooden box
stained black in the inside, and capable of containing from one to
eight persons. It contains a sliding piece, having a sloping mirror
and a double convex lens which may with the mirror be slid up or down
so as to accommodate the lens to near and distant objects. When the
rays proceeding from an object without fall upon the mirror they are
reflected upon the lens, and brought to fall on the bottom of the box,
or upon a table placed horizontally to receive them, which may be seen
by the spectator.


THE MAGIC LANTERN.

This is one of the most pleasing of all optical instruments, and it
is used to produce enlarged pictures of objects, which being painted
on a glass in various colors are thrown upon a screen or white sheet
placed against the wall of a large room. It consists of a sort of tin
box, within which is a lamp, the light of which passes through a great
plano-convex lens fixed in the front. This strongly illuminates the
objects which are painted on the slides or slips of glass, and placed
before the lens in an inverted position, and the rays passing through
them and the lens fall on a sheet or other white surface, placed to
receive the image. The glasses on which the figures are drawn are
inverted, in order that the images of them may be erect.


PAINTING THE SLIDES.

The slides containing the objects usually shown in a magic lantern,
are to be bought at opticians with the lantern, and can be procured
cheaper and better in this way than by any attempt at manufacturing
them. Should, however, the young optician wish to make a few slides of
objects of particular interest to himself, he may proceed as follows:

Draw first on paper the figures you wish to paint, lay it on the table,
and cover it over with a piece of glass of the above shape; now draw
the outlines with a fine camel’s hair pencil in black paint mixed with
varnish, and when this is dry fill up the other parts with the proper
colors, shading with bister also mixed with varnish. The transparent
colors are alone to be used in this kind of painting.


TO EXHIBIT THE MAGIC LANTERN.

The room for the exhibition ought to be large, and of an oblong shape.
At one end of it suspend a large sheet so as to cover the whole of the
wall. The company being all seated, darken the room, and placing the
lantern with its tube in the direction of the sheet, introduce one
of the slides into the slit, taking care to invert the figures; then
adjust the focus of the glasses in the tube by drawing it in or out as
required, and a perfect representation of the object will appear.


EFFECTS OF THE MAGIC LANTERN.

Most extraordinary effects may be produced by means of the magic
lantern; one of the most effective of which is a


TEMPEST AT SEA.

This is effected by having two slides painted, one with the tempest as
approaching on one side, and continuing in intensity till it reaches
the other. Another slide has ships painted on it, and while the lantern
is in use, that containing the ships is dexterously drawn before the
other, and represents _ships in the storm_.

The effects of sunrise, moonlight, starlight, etc., may be imitated
also, by means of double slides, and figures may be introduced
sometimes of _fearful_ proportions.

Heads may be made to nod, faces to laugh; eyes may be made to roll,
teeth to gnash; crocodiles may be made to swallow tigers; combats may
be represented; but one of the most instructive uses of the slides is
to make them illustrative of astronomy, and to show the rotation of
the seasons, the cause of eclipses, the mountains in the moon, spots
on the sun, and the various motions of the planetary bodies, and their
satellites.


THE PHANTASMAGORIA.

Between the phantasmagoria and the magic lantern there is this
difference: in common magic lanterns the figures are painted on
transparent glass, consequently the image on the screen is a circle of
light having figures upon it; but in the phantasmagoria all the glass
is made opaque, except the figures, which, being painted in transparent
colors, the light shines through them, and no light can come upon the
screen except that which passes through the figure.

There is no sheet to receive the picture, but the representation
is thrown on a thin screen of silk or muslin placed between _the
spectators and the lantern_. The images are made to appear approaching
and receding by removing it further from the screen, or bringing it
nearer to it. This is a great advantage over the ordinary arrangements
of the magic lantern, and by it the most astonishing effects are often
produced.


DISSOLVING VIEWS.

The dissolving views, by which one landscape or scene appears to pass
into the other while the scene is changing, are produced by using two
magic lanterns placed side by side, and that can be a little inclined
towards each other when necessary, so as to mix together the rays of
light proceeding from the lenses of each, which produces that confusion
of images, in which one view melts as it were into the other, which
gradually becomes clear and distinct; the principle being the gradual
extinction of one picture, and the production of another.


HOW TO RAISE A GHOST.

The magic lantern, or phantasmagoria, may be used in a number of
marvelous ways, but in none more striking than in raising an apparent
specter. Let an open box, about three feet long, a foot and a half
broad, and two feet high, be prepared. At one end of this place a small
swing dressing-glass, and at the other let a magic lantern be fixed
with its lenses in a direction towards the glass. A glass should now
be made to slide up and down in the groove, to which a cord and pulley
should be attached, the end of the cord coming to the back part of the
box. On this glass the most hideous specter that can be imagined may
be painted, but in a squat or contracted position, and when all is
done, the lid of the box must be prepared by raising a kind of gable at
the end of the box, and in its lower part an oval hole should be cut
sufficiently large to suffer the rays of light reflected from the glass
to pass through them. On the top of the box place a chafing-dish, upon
which put some burning charcoal. Now light the lamp in the lantern,
sprinkle some powdered camphor or white incense on the charcoal, adjust
the slide on which the specter is painted, and the image will be thrown
upon the smoke. In performing this feat the room must be darkened, and
the box should be placed on a high table, that the hole through which
the light comes may not be noticed.


THE THAUMATROPE.

This word is derived from two Greek words, one of which signifies
_wonder_, and the other _to turn_. It is a very pretty philosophical
toy, and is founded upon the principle in optics that an impression
made upon the retina of the eye lasts for a short interval after the
object which produced it has been withdrawn. The impression which the
mind receives lasts for about the eighth part of a second, as may
be easily shown by whirling round a lighted stick, which if made to
complete the circle within that period, will exhibit not a fiery point,
but a fiery circle in the air.


THE BIRD IN THE CAGE.

Cut a piece of cardboard of the size of a penny piece, and paint on
one side a bird, and on the other a cage; fasten two pieces of thread,
one on each side at opposite points of the card, so that the card can
be made to revolve by twirling the threads with the finger and thumb:
while the toy is in its revolution, the bird will be seen within the
cage. A bat may in the same manner be painted on one side of the card,
and a cricketer upon the other, which will exhibit the same phenomenon,
arising from the same principle.


CONSTRUCTION OF THE PHANTASMASCOPE.

The above named figure is a Thaumatrope, as much as the one we are
about to describe, although the term Phantasmascope is generally
applied to the latter instrument; which consists of a disc of darkened
tin-plate, with a slit or narrow opening in it, about two inches in
length. It is fixed upon a stand, and the slit placed upwards, so that
it may easily be looked through. Another disc of pasteboard, about a
foot in diameter, is now prepared and fixed on a similar stand, but
with this difference, that it is made to revolve round an axis in the
center. On this pasteboard disc, paint in colors a number of frogs in
relative and progressive positions of leaping; make between each figure
a slit of about a quarter of an inch deep: and when this second disc
is made to revolve at a foot distance behind the first, and the eye is
placed near the slit, the whole of the figures, instead of appearing
to revolve with the disc, will all appear in the attitudes of leaping
up and down, increasing in agility as the velocity of the motion is
increased. It is necessary, when trying the effect of this instrument,
to stand before a looking-glass, and to present the painted face of the
machine toward the glass.

A very great number of figures may be prepared to produce similar
effects--horses with riders in various attitudes of leaping, toads
crawling, snakes twisting and writhing, faces laughing and crying,
men dancing, jugglers throwing up balls, etc.; all of which, by the
peculiar arrangement above detailed, will seem to be in motion. A
little ingenuity displayed in the construction and painting of the
figures upon the pasteboard disc will afford a great fund of amusement.


CURIOUS OPTICAL ILLUSIONS.

One of the most curious facts relating to the science of vision is
the absolute insensibility of a certain portion of the retina to the
impression of light, so that the image of any object falling on that
point would be invisible. When we look with the right eye, this point
will be about fifteen degrees to the right of the object observed, or
to the right of the axis of the eye, or the point of most distinct
vision. When looking with the left eye, the point will be as far to the
left. The point in question is the basis of the optic nerve, and its
insensibility to light was first observed by the French philosopher,
Mariotte. This remarkable phenomenon may be experimentally proved in
the following manner:--

Place on a sheet of writing-paper, at the distance of about three
inches apart, two colored wafers; then, on looking at the left-hand
wafer with the right eye, at the distance of about a foot, keeping the
eye straight above the wafer, and both eyes parallel with the line
which forms the wafers, the left eye being closed, the right-hand wafer
will become invisible; and a similar effect will take place if we close
the right eye, and look with the left.


ANOTHER.

Cut a circular piece of white paper, about two inches in diameter, and
affix it to a dark wall. At the distance of two feet on each side, but
a little lower, make two marks; then place yourself directly opposite
the paper, and hold the end of your finger before your face, so that
when the right eye is open it shall conceal the mark on your left, and
when the left eye is open the mark on your right. If you then look with
both eyes at the end of your finger the paper disc will be invisible.


ANOTHER.

Fix a similar disc of paper, two inches in diameter, at the height of
your eye on a dark wall; a little lower than this, at the distance
of two feet on the right hand, fix another of about three inches in
diameter; now place yourself opposite the first sheet of paper, and,
shutting the left eye, keep the right eye still fixed on the first
object, and when at the distance of about ten feet, the second piece of
paper will be invisible.


THE PICTURE IN THE AIR.

One of the numerous optical illusions which have from time to time been
evolved by scientific minds, is that of making an image or picture
appear in the air. This is produced by means of a mirror, and an object
in relief, upon which a strong light is thrown--the mirror being set at
such an angle as to throw up the reflection of the image to a certain
point in the view of the spectator. This illusion is produced as
follows: Let a screen be constructed in which is an arched aperture,
the center of which may be five feet from the floor; behind the screen
is placed a large mirror of an elliptical form. An object is now placed
behind the screen, upon which the light of a strong lamp is thrown from
a point above the mirror, and is received by the mirror and reflected
to the center of the arched cavity in the screen, where it will appear
to the spectator. Care should be taken to place the image in an
inverted position, and the light, which must be very powerful, should
be so placed that none of it may reach the opening.


TO SHOW THAT RAYS OF LIGHT DO NOT OBSTRUCT EACH OTHER.

Make a small hole in a sheet of pasteboard, and placing it upright
before three candles, placed closely together, it will be found that
the images of all the candle flames will be formed separately on a
piece of paper, laid on the table to receive them. This proves that the
rays of light do not obstruct each other in their progress, although
all cross in passing through the hole.


OPTICS OF A SOAP-BUBBLE.

If a soap-bubble be blown up, and set under a glass, so that the motion
of air may not affect it, as the water glides down the sides and the
top grows thinner, several colors will successively appear at the top,
and spread themselves from thence down the sides of the bubble, till
they vanish in the same order in which they appeared. At length a black
spot appears at the top, and spreads till the bubble bursts.


THE KALEIDOSCOPE.

If any object be placed between two plane mirrors, inclined towards
each other at an angle of thirty degrees, three several images will
be perceived in the circumference of a circle. On this principle is
formed the kaleidoscope, invented by Sir David Brewster, and by means
of which the reflected images viewed from a particular point exhibit
symmetrical figures, under an infinite arrangement of beautiful forms
and colors. The kaleidoscope may be bought at any novelty store, but
it is requisite that every young person should be able to construct
one for himself. He must, therefore, procure a tube of tin or paper,
of about ten inches in length, and two and a half or three inches in
diameter. One end of this should be stopped up with tin or paper,
securely fastened, in which is to be made a hole, about the size of a
small pea, for the eye to look through. Two pieces of well-silvered
looking-glass are now to be procured; they must be not quite so long
as the tube, and they should be placed in it lengthways, at an angle
of 60 degrees, meeting together in a point, and separating to an angle
wide enough to insert the third piece; the polished surfaces looking
inwards. A circular piece of the glass is now to be laid on the top of
the edges of the reflectors; which, by their not being quite so long as
the tube, will allow room for its falling in, and it will be supported
by the edges of the tube, which may be slightly bent over, to prevent
the glass from falling out. This having been done, now proceed to make
the “cap” of the instrument. A rim of tin or pasteboard must be cut,
so as to fit over the glass end of the tube; and in this, on the outer
side, a piece of ground glass must be fastened, so that the whole may
fit on the tube like the lid of a pill-box. Then, before putting it
on, obtain some small pieces of broken glass of various colors, beads,
little strips of wire, or any other object, and place them in the
cap; and by passing it over the end, so that the broken glass, etc.,
has free motion, the instrument is complete. To use it, apply the eye
to the small hole, and, on turning it, the most beautiful forms will
appear, in the most wonderful combinations.

The following curious calculation has been made of the number of
changes this instrument will admit of. Supposing it to contain 20 small
pieces of glass, and that you make 10 changes in a minute, it will
take an inconceivable space of time, _i.e._ 462,880,899,576 years, and
360 days, to go through the immense number of changes of which it is
capable.


SIMPLE SOLAR MICROSCOPE.

Having made a circular hole in a window-shutter, about three inches
in diameter, place in it a glass lens of about twelve inches focal
distance. To the inside of the hole adapt a tube, having at a small
distance from the lens a slit, capable of receiving one or two very
thin plates of glass, to where the object to be viewed must be affixed
by means of a little gum-water exceedingly transparent. Into this tube
fit another, furnished at its extremity with a lens half-an-inch focal
distance. Place a mirror before the hole of the window-shutter on the
outside, in such a manner as to throw the light of the sun into the
tube, and you will have a solar magic lantern.

The method of employing this arrangement of lenses for microscopic
purposes is as follows:--Having darkened the room, and by means of the
mirror reflected the sun’s rays on the glasses in a direction parallel
to the axis, place some small object between the two movable plates
of glass, or affix it to one of them with very transparent gum-water,
and bring it exactly into the axis of the tube; if the movable tube be
then pushed out or drawn in, till the object be a little beyond the
focus, it will be seen painted very distinctly on a card, or piece of
white paper, held at a proper distance, and will appear to be greatly
magnified. A small insect will appear as a large animal, a hair as big
as a walking-stick, and the almost invisible eels in paste or vinegar
as large as common eels.




THE MICROSCOPE.


At any time of the year or hour of the day there are few pursuits more
interesting, and at the same time instructive, than the study of Nature
by means of the microscope.

All of us must admire the more than awful grandeur of that universe
whereof we form so infinitesimal a part, wherein the stars are
scattered as the sand on the sea-shore, and every star a sun, the
center of a system of orbs too distant for the eye of man to perceive.
Looking at our nearest planet, and observing on her face vast
mountain-chains, ravines into which the light of the sun can never
penetrate, and volcanoes whose craters are so wide that they would
take in the whole of New York, the whole of Philadelphia, and all the
country between them, we can judge by analogy of the unseen wonders
which must exist in the world beyond our ken.

But to him who can read Nature rightly, the microscope is a teacher as
grand as its sister instrument, and the awful magnificence of Nature
is as evident in a midge’s wing as in the more patent glories of the
sun, moon, and stars. In the following pages we hope to put the readers
of this book in the way to read their microscope rightly--possibly
to make it--and to show that much can be done with small means when
“there’s a will,” and to indicate to them that objects of no small
interest can be found without stirring from the room in which we sit,
or even from the table on which our microscope is placed.

Some of our readers may say, when they read the heading of this paper,
that they should like a microscope very much, but that they have no
money to buy it, and that their parents cannot afford one.

This is just the feeling which we used to have when a boy, for in
those day microscopes were microscopes indeed, and you had your choice
between a little instrument, with a series of brass cups, having
glasses in them, which magnified slightly but defined clearly, or a
great composition of brass and iron, looking like a rocket-tube, with
an eye-piece at one end and a glass shot at the other. It was very
costly, very imposing, and magnified very highly; but it strained the
eyes painfully, had no defining capacities, and made all the objects
look as if they were seen through a thick fog. Practically, therefore,
the former was the only instrument that was available.

A still more useful instrument, however, was that which can always be
obtained for a dollar or so, and which is now made wonderfully cheap
and wonderfully good; we mean the double or treble pocket-lens. So
we say, if you cannot afford a really good microscope, do not waste
your money upon inferior and pretentious instruments, but get a sound
pocket-lens.

It has a thousand advantages. It is portable, and is even more useful
in the fields than in the house. It defines very clearly, and needs
little trouble in manipulation. We need not say how difficult is the
task of getting a complicated instrument to define properly, how
impossible with a bad one. The object and the glass can be held in any
light,--a matter of no small consideration when examining anything
new, and trying to make out its structure. It is not easily put out
of order, and if treated with the most ordinary care, will last for a
lifetime.

You can push it under water, and it will magnify as well as in the
air; and if you are wandering on the river-side, you can lie down
on the bank, dip the upper part of your head in water, together
with the glass, and watch carefully the sub-aquatic objects without
removing them. The water will not hurt the eye in the least, though
a non-swimmer may perhaps find a little difficulty in his first
attempt. It makes a good burning-glass, should fire be needed, and no
other means of procuring a spark be at hand. It can be used so as to
show the principle of a camera obscura, and to illustrate the manner
in which photographic portraits are taken. It can be made into an
admirable dissecting microscope, and needs scarcely any practice in
the manipulation. These are some of its advantages, and there are many
others which need not be mentioned.

Even if you should be able to procure a good microscope, get a
pocket-lens as well, for you will want them both, and we may say that
the most practiced microscopists, and those who are possessors of the
most elaborate instruments, are the very men who are the most certain
to have a pocket-lens about them, and to use it most frequently.
Practice well with the pocket-lens before you meddle with the compound
microscope. You will waste no time, but will rapidly gain by it; for
you will be learning the rudiments of a new science, and laying a solid
foundation on which to build.

One or two practical remarks on the proper handling of the pocket-lens
may be of use. Do not always employ the same eye in looking through the
lens, but use the eyes alternately. There is always a temptation to
employ the same eye, which receives a kind of training in vision; but
it is a temptation always to be resisted. With some persons the right
eye is most in favor, and with others the left; and when the favorite
eye gets all the work, it too frequently suffers. Whether you look with
the right or the left eye, _keep both eyes open_.

At first the beginner will find a little difficulty in restricting his
vision to one eye while the other remains open, just as a beginner
on the piano-forte feels himself puzzled when he tries to make his
right hand go one way and his left hand another; but in either case a
little practice and plenty of perseverance are sure to overcome all
obstacles, and in a wonderfully short time the difficulty will not only
be overcome, but forgotten.

We speak here with some feeling, because, while engaged on a work on
the microscope, we were necessarily obliged to work much at night,
and inadvertently employed the left eye more than the right; the
consequence of which imprudence was that we have been obliged ever
since that time to give the left eye perfect rest, as far as artificial
vision goes, and, except when looking through a binocular instrument,
we have not ventured to use it either to a microscope or a telescope.
The vision accommodates itself to circumstances with wonderful
ease, and the observer learns the curious art of cutting off all
communication between the unused eye and the brain; so that, although
the objects around may imprint themselves upon the retina, the mind is
as totally unconscious of them as if they had no existence.

If possible, always examine an object _without removing it_, as thereby
you see it as it is, without altering any of the conditions with which
it is surrounded. Should this not be practicable, take the object to
be viewed in the left hand and the lens in the right. Place the wrists
of the two hands together, and then you will find that one supports
the other, and that the lens can be held in the proper focus without
the least difficulty. After you have used the lens for some little
time, you will learn to hit upon the right focus almost to a hair’s
breadth,--so as to lose no time, a matter of some importance when a
living creature is to be examined, especially if it be in motion.

We are now about to suggest a very simple piece of mechanism, by which
the pocket-lens can be converted into a microscope that will serve for
dissection and many other purposes.

Melt three or four pounds of lead in an iron ladle, and make a mold,
consisting of a hollow hemisphere of paper or cardboard, through the
center of which an iron rod has been passed. The hollow of the paper
should resemble an ordinary saucer. Pour the lead into the saucer, and
let it cool. The paper mold will be scorched by the heat and rendered
useless, but an outer coating of lead will be cool and hard before the
paper is quite destroyed. Next take a piece of stout brass wire and a
wine-cork; twist the wire round the cork several times; cut off one end
close to the cork; sharpen the other, and turn it up.

Bore a hole through the cork, just large enough to allow the upright
rod to slip through it, and there is the “stand” of your microscope.
Now take your pocket-lens, and get an optician to bore a hole through
one end of it, just large enough to receive the upturned end of the
wire; slip the lens on the wire, and the microscope is complete.

The cork, though grasping the upright stem with tolerable firmness,
can be slid up and down so as to insure the correct focus, and can be
pushed aside whenever the object has to be viewed with the naked eye,
and must not be removed from its place. This instrument is a capital
one for dissecting purposes, and will answer quite as well as those
expensive affairs that are to be purchased in the shops.

If the object be transparent, and requires to be seen by transmitted
light, the following plan will answer:--Take a thin piece of wood, cut
or punch a round hole out of the middle, and support it on four legs.
Wires or wooden pegs fixed in corks will answer the purpose well, and
if the corks be glued to the corners of the board, the legs can be
inserted or removed at pleasure. The wood of which cigar-boxes are
made will answer the purpose very well. Its dimensions should be about
three inches in length by two in width. Now buy one of the doll’s
looking-glasses that are sold for a penny, and put it under the stand.
Lay a flat piece of glass over the hole, place the object upon it, and
direct the light through it by means of the mirror below. If such a
mirror cannot be obtained, it is easy enough to make one, by mounting a
piece of looking-glass in a cork frame, and making it swing on pivots,
like the glasses of our dressing-rooms.

The young microscopist must remember that when he is examining
any object by transmitted light, he must arrange it as flatly as
possible on the glass. In many cases, a still neater manipulation
is required--as, for example, when the petals of flowers are under
examination. Thin glass is to be purchased at any optician’s, and if
cut in squares, instead of circles, is very much cheaper, and quite as
useful for all practical purposes. Lay the petal on the glass plate,
place a piece of the thin glass upon it, and press it gently while
examining it. If it still remains thick and dull, put a drop of pure
water on the petal, and replace the thin glass, when the structure will
almost invariably be detected.

Everything depends on the proper management of the object and the
arrangement of the light. Some opaque objects can be seen best by
direct light, and others by transmitted light. If a leaf be examined,
particularly if it be a thick and heavy one, like that of the ivy,
the upper and lower membranes must be stripped apart--a task which is
easily performed by tearing a small slit, and then ripping it smartly
across. A pair of forceps will be required for this and other delicate
work, and may be obtained at a cheap rate. Care must be taken to keep
the points exactly even, and if at any time one of them appears to be
shorter than the other, they should be rubbed on a hone until they are
brought perfectly level.

These should be made of steel; but the young microscopist will find
that a second pair, made of brass, and much rougher in finish, are
invaluable aids as he takes his walks into the country. By their aid
he can pick up minute objects, draw insects out of crevices without
damaging them, and pluck the tiniest flowers without harming their
petals. They can be carried in the waistcoat pocket, and the cost is
sixpence. Any lad who knows how to handle solder can make a pair for
himself in a few minutes.

A penknife with one blade kept scrupulously sharp is essential, and we
have found an old lancet of the greatest service. Lancets have gone
so much out of fashion, that the second-hand instrument shops abound
with them. We did not allow our own lancet to be shut up, but removed
the blade from the tortoise-shell handle, and fixed it upon a wooden
handle, about four inches in length, so that it looked very clumsy, but
was extremely useful.

Two pairs of scissors are needful,--one very fine and the other
moderately strong. Both pairs, however, must have very short blades
and very long handles, and the scissors such as ladies use are of very
little use, the short handles causing the fingers of the right hand to
shade the object. As to the fine pair, it is hardly possible to have
the handles too long or the blades too short; for if the points can be
separated a quarter of an inch, nothing more is needed. If a pair of
bent scissors can also be obtained, they are extremely pleasant to work
with, and save much trouble.

Pill-boxes of various sizes are of very great service to the
microscopist. We always have them arranged in “nests,” _i. e._, six or
seven inside each other, so that space is greatly economized, as long
as they are not in absolute use. All delicate objects should be placed
in separate boxes, and the predaceous insects must be treated in the
same manner, or they will certainly destroy one another, or, at all
events, inflict such injuries as will make them useless for microscopic
purposes.

When the insects are to be killed on the spot, we employ another and a
very simple plan.

We take one of the old-fashioned wooden lucifer-match boxes, bore a
hole in the lid, and push through the hole a swan-quill, or the barrel
of one of the swan-quill steel pens. A glass tube is still better, but
is too fragile. Beeswax is tightly worked into the junction of the tube
with the wood, so as to make it as nearly air-tight as possible. A cork
stopper is then cut to fit the tube. When this is finished, we take the
smallest-sized pill-box, bore a number of holes in it with a red-hot
needle, place a little piece of solid ammonia within it, and inclose it
in the lucifer-box. Its effects are almost instantaneous; for scarcely
has the insect touched the bottom of the box before it is helpless, and
in a very few moments it is quite dead, so powerful is ammonia towards
insects. The reader will of course understand that the pill-boxes
must never have been used for pills, and that the match-box must be
carefully cleaned before employing it in the microscopic service.
Moreover, any boxes that have been used for insects become useless,
inasmuch as the scales always fall from the wings, and cling to the
sides of the box, so as to mix with succeeding objects, and very much
puzzle the observer.

Aquatic and marine objects require bottles, and, as a general rule,
these bottles ought always to have wide mouths. Indeed, if there be no
shoulder at all, their purpose will be better served, as a small object
is very apt to be caught under the shoulder, and to give much trouble
before it can be removed without injury. Wide and short test-tubes
answer admirably for collecting; and it will always be advisable to
have a few small test-tubes ready fitted with corks, for the purpose of
isolating those specimens which might receive or cause injury by being
mixed with others.

To remove minute objects from one vessel into another is a very easy
process. Take a glass tube, mark off a portion about eight inches in
length, cut a little notch with a file, and bend it smartly, when
it will break neatly across, without leaving points or having the
regularity of its ends injured by gaps. Turn each end round and round
in the flame of the spirit-lamp, and you have an ordinary “pipette.”
The object of placing the ends of the tube in the flame is to render
the edges quite smooth and rounded.

Now mark off the same length of tube, and place the marked portion
in the flame, taking care to warm it well first, lest the sudden
heat should crack the glass. Keep it continually turning between the
fingers, and when it is quite soft, and of a fine red heat, draw the
hands smartly apart, and you will produce a couple of tubes tapering
to very fine points. Break off the tapering portions at any convenient
point, round the edges as before, and you will then have pipettes
suitable for small objects. As there are many specimens, especially the
smaller animalculæ, which have a habit of retiring into the remotest
corner, it is necessary to bend another pipette, so as to follow them.
For our own part, we prefer the pipette to be bent nearly to a right
angle.

The mode of using these simple instruments is as follows:--Place the
forefinger or thumb firmly on the large end, and push the point under
water. When the opening is close to the sought-for object, lift the
finger suddenly, and admit the air into the tube. The water will
immediately rush in at the lower end, and if the orifice has been
properly directed, will carry the object into the tube. The finger is
again applied to the mouth of the tube, and the object can be then
carried off.

As with the pocket-lens almost every object is to be viewed by means
of direct light, the young observer will find himself much aided by
a suitable background. Any small object, such as a minute insect, a
seed, or a hair, becomes very indistinct if held up against the light,
or even when viewed against a broken background of trees, houses, or
herbage. The simplest plan of securing a proper background is to take
a disc of ivory or even of white cardboard, and to blacken one side
of it. The black paint which is used for this purpose must be without
gloss, and have what is called a “dead” surface. Ink answers very well
for the purpose, and so does ivory-black; but Indian ink is too glossy
to be serviceable.

To procure specimens from the water is a matter of some difficulty if
managed badly, but easy enough when the collector knows his business.
It is of course needful to attach the collecting vessel to the end
of a rod, and to plunge it into the spots which look most favorable.
Now even so simple a matter as this requires some little care, if the
young microscopist really wishes to obtain the best specimens. A common
walking-stick will answer most purposes; but the most efficient rod for
the purpose is one of the common walking-stick fishing-rods without the
top joint, as it can be carried without attracting attention, and can
be lengthened at will by adding the different joints.

Many methods have been proposed by which the vessel is to be attached
to the rod; but that which I am about to describe is certainly
the simplest and most effective that I have tried. Get a piece of
gutta-percha tubing, just large enough to be slipped on the end of the
rod or stick; mark off an inch or so, and cut the tube nearly through,
then cut it away longitudinally, so that a long tongue of gutta-percha
is left, and the instrument is completed.

Its application is as simple as its structure. Bend the tongue over,
so as to form a loop, and push the end through the short tube. Slip
the neck of the bottle into the loop, and draw the tongue until it is
tolerably tight. Push the end of the stick into the tube, taking care
to hold the tongue firmly in its place, and the vessel will then be
fastened at right angles to the stick.

The method of collecting by means of this instrument is as follows:
Immerse the vessel in the water, with the mouth downwards, so that
no water may enter. Push it gently towards the spot which is to be
investigated, move it about a little, so as to cause a disturbance, and
then turn the vessel with its mouth upwards. Water will instantly rush
in, carrying with it the objects which are to be examined. The contents
of the vessel may then be transferred to the large bottle, and another
dip made. Confervoid growths, especially those which accumulate in a
kind of scum on the surface, should be obtained very quietly, without
previous disturbance of the water.

After the pond, or stream, or ditch has been well searched, the bottle
should be roughly examined, by means of a pocket-lens, and the contents
sorted into the smaller tubes, as has already been mentioned. This
precaution is especially needful when any of the minute crustacea
called Entomostraca are captured, as they are most voracious beings,
and will make sad havoc among other specimens, unless they are placed
in separate bottles. They are mostly large enough to be detected with
the naked eye, and look something like little fleas as they move along.

As the Entomostraca cast their shells repeatedly during their lives,
some species performing this operation every two days, a beautiful
series of objects can be obtained by gathering the cast shells and
preparing them for the microscope, according to the directions that
will be found in the following pages. These shells are peculiarly
valuable, as they retain the chief external characteristics of the
creature to which they belonged, the limbs, plumes, and even the
delicate bristles being preserved entire. It is in the power of the
microscopist to retard or hasten the change of shell, heat and light
aiding development, and cold and darkness retarding it. The remarkable
“ephippium,” or saddle, which is found on the backs of the Daphnia, the
Moina, and other Entomostraca, and which is used as a receptacle for
eggs, should be searched for and preserved.

A very thin and a very flat bottle is a most useful assistance in
detecting the character of any unknown object, especially if it be
living. Such a bottle may easily be made by heating one of the small
test tubes in the spirit lamp until it is of a glowing red heat, and
then pressing the sides together. Some little neatness is required
in this process, as an unskillful operator is apt to press the sides
unequally, and to leave a bulging projection at the end.


THE COMPOUND MICROSCOPE.

We have already described the simpler forms of magnifying instruments,
together with the best method of using them. We now purpose to describe
the more complicated instrument called the compound microscope, and
hints will be given as to the best method of making preparations for it.

The great distinction between the simple and compound microscope is,
that whereas the former instrument magnifies the object, the latter
magnifies the magnified image of the object. In the least elaborate
form of this instrument there are two glasses, one at each end of
a tube, the small glass magnifying the object, and being therefore
called the “object-glass,” while the other, which magnifies the image
of the object, is placed next to the eye, and is therefore termed the
“eye-glass.” In practice, however, this arrangement is found to be so
extremely defective, that the instrument was quite useless except as
an experimental toy; for the two enemies of the optician, chromatic
and spherical aberration, prevailed so exceedingly, that every object
appeared as if surrounded with prismatic colors, and every line was
blurred and indistinct.

In this uncertain state the compound microscope remained for many
years, its superb capabilities being scarcely recognized. The chief
fault was thought to be in the material of which the object-glass was
made, and for a long series of years all experiments were conducted
with a view to an improvement in this respect. When, however, the
diamond had been employed as an object-glass, and had failed equally
with those of less costly material, attention was directed to the right
point--namely, the arrangement of the different glasses,--and at length
opticians succeeded in obtaining a pitch of excellence which can be
almost termed perfection. It would be impossible to describe the method
which is employed for this purpose, and it must suffice to say that the
principle is that of playing off one defect against another, and so
making them mutually correct their errors.

The magnifying powers of the compound microscope can be very great,
and it is therefore necessary that extreme care should be taken in its
manipulation. It will be possible for a clumsy person to do more damage
to a good instrument in three minutes than can be repaired in as many
weeks.

Before proceeding to the management of the microscope and the
construction of the “slides,” we will briefly describe one or two chief
forms of the compound microscope.

The simplest form of the compound microscope, as at present made,
consists of a stand and a sliding tube, in which are set the glasses
which magnify the object and its image. At the top is the tube, which
is capable of being slid up and down in the shoulder of the stand, so
as to obtain the proper focus. Above is seen the eye-glass; and the
object-glass is shown at the bottom of the tube. Below the object-glass
is the “stage” on which the object to be magnified is laid; and lowest
of all is a mirror, which serves to reflect the light upwards through
the object, and which can be turned by means of the knobs at the
sides. The object-glass is composed of two pieces, which can readily
be separated. If both are used, sufficient magnifying power is gained
to show the scales on a butterfly’s wing and similar minute objects;
while, if one is removed, the object is not magnified to so great
an extent, but a larger portion can be seen, and the definition is
clearer. The cost of this instrument, together with a few accessories,
is about $2.50.

The proper light is our next point, and upon it rests the chief
beauty of the effect. The light which will suit one object will not
suit another, and even the same object should be examined under every
variety of light. Some objects are best shown when the light is
thrown _upon_ them from above, and others when it is thrown _through_
them from below. Again, the direction of light is of vast importance;
for it will easily be seen that an oblique light will exhibit minute
projections by throwing a shadow on one side and brilliancy on the
other, while a vertical illumination would fail to show them. On the
same principle, one object will be shown better with the light in
front, and another when it is on one side.

One of the most effective means of attaining this object is by using
the “bull’s-eye condenser,” which is sometimes fixed to the stage, but
is usually detached. As the upright stem is telescopic, the glass can
be raised to a considerable height, while the joint and sliding-rod
permit the lens to be applied at any angle which promises the most
brilliant light.

As for the kind of light that is employed, there is nothing which
equals that of a white cloud; but such clouds are rare, and are at
the best extremely transient, and can only be seen by day, various
artificial methods of illumination have been invented. Novices
generally think that when the sky is bright and blue they will be very
successful in their illumination, and feel grievously disappointed
at finding that they obtained much more light from the clouds, whose
disappearance they had anxiously been watching. Finding that the blue
sky gives scarcely any light at all, they rush to the other extreme,
turn the mirror towards the sun, and pour such a blaze of light upon
the object, that the eye is blinded by the scintillating refulgence,
and the object is often injured because the mirror is capable of
reflecting heat as well as light.

In the daytime there is nothing better than the “white-cloud
illuminator,” which is made easily enough by means of plaster of
Paris. A sheet of thin white paper fastened against a window-pane is
also useful; and the simple plan of dabbing the glass with putty will
have a beneficial effect in softening the light, when the window has
a southern aspect. In default of these conveniences, it will be often
sufficient to fix a piece of white letter paper over the mirror, or
even to dull its surface with wax. At all events, he who aspires to
be a true microscopist must be ready with expedients, and if he finds
himself in a difficulty, he must summarily invent a method of obviating
it.

At night a lamp is necessary; candles are useless, because they have
two faults--they flicker, and they become lower as they burn. The
latter defect can be cured by using a candle-lamp, but no arrangement
will cure the flame of flickering; it is peculiarly trying to the
eyes, and destructive of accurate definition. An ordinary moderator
lamp answers pretty well, and a small one is even better for the
microscopist than one of large dimensions. The chief drawback to the
moderator lamp is that the flame cannot be elevated or lowered, so
that the only way to procure a light at a higher elevation is to stand
the lamp on a block of wood or a book. Small lamps are, however, made
expressly for the microscope, and, if possible, should be procured, and
used for no other purpose, and intrusted to no other hands.

If you want a really brilliant, clear, white light, you must trim
the lamp yourself. A small piece of pale blue or neutral-tint glass
interposed between the lamp and the microscope has a wonderful effect
in diminishing the yellow hue which belongs more or less to all
artificial lights which are produced by the combustion of oil or fat.
We have no doubt but that in a few years we shall be rid of the clumsy
and dirty machines that we call lamps, and have substituted for them
the pure brilliancy of the electric light.

Whatever lamp you use, a shade is absolutely necessary, in order to
defend the eyes. Let me here warn my young readers that they cannot
be too careful of their eyes. In the exuberance of youthful strength
and health we are too apt to treat our eyes as unceremoniously as our
digestion, and in later years we awake to unavailing repentance.

Another point which calls for extreme attention is the perfect
cleanliness of the glasses. It is astonishing how a tiny dust-mote,
or the least condensation of damp, will diminish the powers of the
microscope, and how often the instrument is blamed for indistinctness
when the real fault lies in the carelessness of the operator. Even
when the greatest care is taken, dust is sure to settle on the
glasses, especially on the eye-piece, and before using the microscope
the glasses ought to be carefully examined. Never wipe them with an
ordinary handkerchief, but get a piece of new wash-leather; beat it
well until no dust issues from it, and then put it into a box with a
tightly-fitting cover. Use this, and nothing else, for cleaning the
glasses, and you will avoid those horrid scratches with which the
eye-glass and object-glass of careless operators are always disfigured.

Moisture is very apt to condense on the glasses and to ruin their
clearness. If the microscope be brought from a cold into a warm room,
the glasses will be instantly covered with moisture, just as the
outside of a tumbler of cold water is always covered with fine dew
when brought into a warm room. The microscope should therefore be
kept at least an hour in the room wherein it is to be used, so that
the instrument and the atmosphere may be of the same temperature.
You should make the microscope a trifle warmer than the surrounding
atmosphere, and so avoid all danger of condensation. When changing
the object glass or eye-piece, always keep the hand as far away from
the glass as possible, and manipulate with the tip of the forefinger
and thumb. The human skin always gives out so much exhalation, that
even when the hand is cold the glasses will be dimmed; and it is a
peculiarity of such moisture, that it adheres to the glasses with great
pertinacity, and does not evaporate like the dew which is condensed
from the atmosphere.

In order to insure perfect success in this important particular, the
young microscopist will do well to get the optician from whom he
purchased his instrument to explain its construction, and to give him a
lesson or two in the art of taking it to pieces and putting it together
again; for unless each glass can be separately cleaned, no one can be
quite sure that the instrument will perform as it ought to do. The best
method of ascertaining whether it is quite clean is to throw the light
upwards by means of the mirror, and then to turn the eye-piece slowly
round. If any dust or moisture has collected either upon the eye-glass
or the “field-glass,” which forms the second lens of the eye-piece,
it will be immediately detected. Turning the object-glass will in a
similar manner detect impurities upon its surface.

THE END.

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Transcriber’s Notes:

Punctuation has been made consistent.

Variations in spelling and hyphenation were retained as they appear in
the original publication, except that obvious typographical errors have
been corrected.

The notation 1-2 for fractions has been standardized to the current
convention 1/2.