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The Table of Contents was created by the transcriber and placed in the public domain.

[Additional Transcriber’s Notes] are at the end.

CONTENTS

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.

WITHOUT SNOW OR ICE.

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.