How to Make Electrical Machines / Containing Full Directions for Making Electrical Machines, Induction Coils, Dynamos, and Many Novel Toys to Be Worked by Electricity

The soft iron cores have now to be converted into magnets as usual, and here comes in the especial advantages of having screws to fasten the magnet together, as you can take the whole thing to bits, wind the wire on the legs in comfort, and then fasten together again. But if you have soldered the magnet together, you can achieve the same end in a different way by making two small bobbins to hold the wire, the exact size to slip on over the soft iron cores when the wire is wound on them. It is generally considered proper to wind the wire on bobbins, which can be removed from the cores if required. I should think it can seldom be required, but the bobbins are convenient in this case. I may remark parenthetically that bobbins wound and unwound, soft iron cores, and yokes, separately or together, and supports fixed to the yokes or not, can be obtained from any large electrician who sells parts of electric bells, etc.; the magnet can also be got put together complete.

We now have to make bobbins, supposing that we are not going to buy them. The elaborateness of their manufacture will depend entirely on the skill of the maker. Some construct them by sawing off top and bottom of a reel of cotton, and forming a roller of cardboard to fit the magnets, finally joining the ends of the reel to this roller, to make an elongated reel of the right size. Others construct their bobbins entirely of cardboard, the ends being merely two circles of card. Others who are versed in the mysteries of wood-turning, and are lucky enough to possess a lathe with which to do it, make two bobbins of solid wood, drilled to fit the iron cores. For these no instructions are needed, as the dimensions will be as given presently. For those who only want to use the magnet for this special purpose, and do not care about the bobbins being removable, the following is the simplest way to set to work:

Cut two circles of thick cardboard, each ⅞ inch in diameter, and in the center cut a hole the exact size to slip over the soft iron core. Now wrap several thicknesses of thin tissue paper—or preferably French note paper or tracing paper—over the magnet, between the circles of cardboard, cutting the strip about 1⅛ inch broad or ⅜ inch less than the length of the cores. Now you can fasten the two circles of cardboard at the ends of the tracing paper, and keep them in their proper places on the magnet by means of mucilage—beat the soft iron before applying, and it will then adhere firmly to it. In this way, of course, you form a roller, on which we now have to wind the wire. If you have soldered the magnet’s parts together, you must have movable bobbins, as it would be simply impossible to wind the wire evenly on the cores when fixed in position, as the edges of the bobbins will be so close together that it is not possible to wind the wire on between them without the coils becoming displaced.

The method of winding the wire is simple enough. No. 24 wire is a good size to use; it can be cotton-covered or, preferably, silk-covered, as in the latter case the insulation is better. Begin by making a hole near the roller in the circle of cardboard that is next to the end where the hole for the screw has been made. Pass about three inches of wire through the hole and then wind it evenly on over the tracing paper from end to end and back again. You ought to have five or six layers of it; an ounce, or an ounce and a half, of wire will probably be enough. When it is all on, make another hole in the disc and pass out the wire. This is only to hold it safe while you wind the other bobbin. When that is finished you can put the magnet together, and ends of the two wires have now to be joined together. The two ends that are joined together must be those which come from the wire that is wound from the right to the left over one core and left to right over the other, that is to say, taking the wire when joined as one, it must be so wound on both limbs of the magnet that if they were bent into one straight bar it would all be wound in the same direction.

With a composite magnet, however, there is no earthly difficulty in getting it right, for you have only to connect the battery to two wires and join the other two, and if they don’t make the magnet work, join up one to the battery instead of one of those joined, and connect the other two wires; whichever gives the best result stick to. You must get all the silk or cotton off the wire, where you join them, and twist them over and over tightly together; if you can solder them, so much the better. Pull the wire tight and wind it on the reels until the place where it is joined is pulled tightly and not left in a loop, which would look untidy. Fig. 2 gives an idea of the magnet completed, and I have endeavored by means of the arrows to show how the wire is wound, they are supposed to give the direction of the top layer of wire in each case; of course either may be wound from the inside, so you must also consider that in this picture the outside coils are joined. The magnet having been thus constructed, we must now turn our attention to the vibrating hammer which is to beat the drum. To make this we want another piece of soft iron of about the same size as that forming the yoke of the magnet, say, 1⅜ inch × ½ inch × ⅛ inch. We shall then require a piece of brass spring about three inches long and half an inch broad. This is made of very thin springy brass, so as to make a spring which will move the armature quickly. One end of the spring should be tapered off as shown in Fig. 3, and at the point P in the figure a small piece of platinum foil (the real thing, not tin-foil, which I am sure is often sold in cheap apparatus instead of it,) should be fastened, by solder if possible.

We now want a piece of rather stout brass wire bent into the shape shown in Fig. 4. It must be about four inches long, but its length will be determined by the size of the drum and the length of the magnet when it is all put together. At the end of this wire you must have a wooden knob (not brass, which doesn’t produce nearly so much noise). This you will have provided ready for you if you purchase the drum, as they will naturally supply drumsticks with it, and the head of one of these cut off and fastened to the end of the wire, by simply making a hole and sticking it in, will answer the purpose beautifully.

This wire has to be fastened to the soft iron armature, a simple way of doing which is to drill a hole the exact size and insert the end; it can then be soldered in. Or, if you cannot drill a hole, you can simply solder it on. The brass spring has the end bent outwards, as shown in Fig. 4, and is fastened to the soft iron armature by screws, as shown in the figure at S S, or simply soldered on. The point C is the end that is tapered off, and the platinum wire is fixed at that point; the spring should extend about 1¼ inch beyond the armature at the other end. Two holes are drilled in the spring at the points H H, through which screws are passed into the support. This support may be either a piece of iron ½ inch long, ¾ inch broad and ¾ inch thick, or a piece of wood will answer very well, and save drilling holes in the iron. If it is wood it had better be larger, say ¾ inch by ¾ inch by 1¼ inch.

PART IV.

We can now proceed to fasten all the parts together. We must have a piece of hard wood for the base, about 3½ inches by 3 inches and ⅜ inch thick. On this the magnet has to be fastened by its support being screwed firmly down. In front of it the armature has to be fastened at such a height as to be exactly in front of the poles of the magnet. The relative positions of the parts are shown in Fig. 5, so I do not think a detailed account of their exact positions on the base is at all necessary.

There is, however, one piece of the mechanism in the figure to which I have introduced you, this is the contact-screw shown at C. To make this we take a piece of brass about 1½ inch long, ½ inch broad, and rather less than ⅛ inch thick, and bend it at right angles, so that one leg is one inch long and the other ½ inch. Now in the part that is ½ inch have to be drilled three holes to fasten it with nails or screws to the base. The other part, one inch long, will then stand erect, but before fastening it in its place we put it to stand in front of the magnet and mark a point which is exactly on a level with the piece of platinum foil on the spring, when the spring and magnet are fixed in position. A hole has now to be drilled through that point and tapped to admit a brass screw with a milled head, and fix the piece in which the screw works to the front hole, so that the screw will work through it.

The point of the screw has now to be cut off and a very small piece of platinum wire fixed at the end. This wire will now come in contact with the platinum foil on the spring, when the brass support is fixed in a certain position on the base, and it is now to be fixed in that position with screws or nails. It should be so fixed that when the screw is turned till it is nearly out of its hole the wire is just out of contact with the platinum foil on the spring. It is now evident that by turning the screw one way you make the spring vibrate more rapidly, and by turning it the other way its efforts are relaxed.

The contact-breaker screw having been fixed in its place, and the support of the spring also fixed as at T in the diagram (Fig. 5)—by screws through the base into the iron, if it is made of iron, or by nails or screws through it into the base if of wood—all the parts are now together, and all that remains to be done is to make the necessary connections. One wire that comes from the magnet is to be joined (soldered, if possible,) to the spring at H in the picture; the other wire is left loose. To the brass support of the contact screw we solder another piece of wire. Now this piece of wire is connected with the zinc of the battery and the other (coming from the coil of the magnet) with the carbon of the battery. What happens?

The electricity passes along the wire X, we will say, and round the magnet coils, thus turning the cores into magnets. It then goes down the other wire to H, up the brass spring, along the screw, and down by the brass support to the other wire, by which it returns to the battery. That is to say, it would do all this if the armature stood still, but, of course, when the cores become magnets they attract the armature, which instantly moves towards them; this breaks the circuit, the spring moving off the platinum point of the screw, and the armature springs back again, which makes the circuit complete and the magnet attracts it again, and so on. The object of the spring is to get a good deal of vibration, and it and the screw should be so adjusted that although the armature is close enough to the magnet to make it certain to “go off” directly it is meant to do so, yet there may be as much scope for the spring to work with elasticity as possible.

We have now completed the electrical part of the business, but a slightly necessary part of the apparatus has yet to be obtained—viz., the drum. You can easily make a drum if you like, by taking a broad piece of tin, twisting it round to form a hoop, and covering the ends with parchment strained tightly over them. However, I should certainly not do so, for there can hardly be any spot, I should think, which boasts of a toy-shop at all, where drums cannot be procured! For twenty-five cents you can get a very superior drum, just about the right size; if you like to get a bigger one and make the mechanical part bigger, you will, of course, be rewarded by more noise.

Now, suppose you have got a 25-cent toy-drum, you must proceed to take off one end. If you look at the construction of the drum you will find (at least it is the case with my own, and I have not seen any that are differently made) that by cutting one of the double strings that fasten the wood hoops at the top and bottom together, and then loosening all the other strings with your fingers, the wooden hoop at one end will come right off, if the nails fastening the ends together are taken out, and that then the inner hoop on which the parchment is stretched will also come off and leave that side of the drum open.

Now, this is simply grand for our purpose, for when we have arranged our little dodges inside the drum, we can put on all the hoops again, replace the one double string, and no one will be an atom the wiser. If you could get off the side without breaking any strings it would save the trouble of replacing any, but I am afraid this is hardly possible. However, off comes the side of our drum, and what is to be done next? Well, the “beater” must be put bodily inside the drum, just so close to the parchment side that was taken off that the wooden head of the drumstick touches it when attracted by the magnet. You can easily find the right place in actual practice by setting the beater going and finding the spot inside the drum where it kicks up the worst racket when working. It must not be too close or it will hinder the vibration, and we want the hammer to go off instanter when required. The beater is fixed to the side of the drum with its side marked Z in the figure (5) downwards. It is easily fastened there by making two holes in the wood (in the thickness of it), and two corresponding holes in the metal side of the drum, and then screwing it down in its proper place.

Two holes are to be made in the side of the drum and two ornamental bits of silk-covered flexible copper conductor let through. They can be secured by simply tying knots inside the drum, and the copper ends are now to be fastened, one to the wire X and the other to the wire K from the contact screw support. Having done all this and made sure that the beater works when the ends of the flexible cord outside the drum are connected with the battery, we seal up our drum again, and that is then concluded.

Now as to fixing it up, I think I may fairly assume that you know how to make it work by an ordinary battery and a “press.” It is only necessary to run a double wire from battery to press and from press to drum, one wire of the double conductor being fastened to the carbon end of the battery and the other to the zinc end, and the other end of one wire to one of the wires coming from the drum. The other wire coming from the drum is then joined to the bottom conductor of the press, and the upper conductor of the press is joined to the other wire of the double conductor that goes to the battery. It is all very easy to understand if you follow the course of the current and consider that it has to pass through the drum and the press when the latter is pushed down, and be stopped when it is left to spring up again.

But the more magical arrangement can be made with the drum, and I think it is well worth while to do it, if merely for the fun of mystifying people. The drum is going to be suspended by the flexible cords; therefore, let them be the same length, and cutting off all the coverings at the end of each, fasten a brass “eye” to the copper, twisting the wire well round the bottom of the eye. Now wind silk of the same color as the rest all round the join, so that the connection of wire and eye is completely hidden, and the eye appears merely fastened to the flexible cord as a means of suspending the drum. Now we want to construct a hook from which the drum can be hung.

PART V.

Take two small pieces of brass wire about an inch long, and turn up the ends of each into a hook. Now get a minute piece of ebonite of the same length, and, putting one hook on one side and one on the other, bind the whole together with silk. If you cannot get ebonite easily you can use a small piece of sealing-wax in the same way; by heating the wires you can sink them into the wax and so make a neater join. Now the wires must not touch each other anywhere, but must be completely separated by the ebonite or sealing-wax. The double wire from the battery and press is now fastened, one wire to the press hook on one side, and one wire to that on the other side of the sealing-wax or ebonite. Wind silk over the whole to cover the joins, and a neat double hook is the result. The picture (Fig. 6) gives the method of making the hook, and it also gives a great deal more, which I now proceed to explain.

Supposing we can rig up a small beam of wood from which to suspend the drum, we can make matters more mysterious still. Let the double wire, being hidden by some means or other all along its course, be conducted on to the end of the beam. It can then be trained along the top of it until it comes to the point from which the drum is to hang. Here there must be a hole drilled, large enough to admit the hook rather tightly. Pull the double wire through and fasten the two wires to the hooks as before described.

Now you can pull back the wire and fix the hook firmly in the hole, hiding the double wire at the top of the beam (of course if it is high up no one will be able to see over the top of the beam, so you will be quite safe); the hook being thus fixed will not attract any one’s notice, and look quite unsuspicious. The chief glory of the double hook thus constructed is, of course, that you can remove the drum whenever you choose, for examination, and whenever you hang it up you have only to hitch one eye over one side of the hook and the other over the other side, and the drum will work. People who are not up in the matter cannot conceive how the electricity can get to the drum, when it is simply hung by an (apparently) ordinary cord and ordinary eyes to what looks like an ordinary hook attached to a beam in a plain and straightforward manner.

You are now possessed of an electric trumpet and an electric drum, which you can put one at one end of the room and the other at the other. By running double wires from battery and press to the trumpet, and another double wire from battery and press to the drum, you can arrange matters so that when you put one press down the trumpet works, and when the other press is put down the drum works. If you want to work both together you must either have a very powerful battery (say 6 or 7 cells, No. 2 Lechlanche) or two batteries, one for trumpet and one for drum. If you want to use one battery for both you can make either work (at different times) from the same battery and presses, wherever they may be, by having a two-way switch in a dark corner of the wire.

It is very confusing business setting up the wires so as to produce the right effect, which is to change the current from drum to trumpet and vice versa in a moment by merely altering the handle of the switch. Readers who are not accustomed to the work will find it most intricate, and as I have done it myself several times, they may as well have the benefit of my trouble. I therefore give an illustration of how to connect up the wires (Fig. 7), and hope it will make matters clear to them. An explanation of the picture is necessary.

Suppose first of all that the switch is at A C, then the current will travel from the right-hand end of the battery, B, up one wire of the double conductor to the press, P, as shown by the lower arrow, through the press and along the wire, as shown by the top arrow, to the middle of the switch, A, down the arm of the switch to C, up one wire of the double conductor to the drum, and down by the other wire to the other end of the battery.

Now let the handle of the switch be moved to the other terminal, as shown by the dotted lines. The current will now go from the right-hand end of the battery to press and center of switch as before, it then goes down the arm of the switch up to the trumpet by the wire on the left side, and down to the other end of the battery by the wire on the right side, as shown by the arrows. Therefore when the arm of the switch is at A C the press will work the drum; when it is at A G the press will work the trumpet.

Suppose we have no press, but instead of it we have only one wire going straight from the right-hand end of the battery to the middle of the switch. Now let two incandescent lamps be substituted for the trumpet and drum. When the arm of the switch is at A C the current goes straight up from the right-hand pole of the battery to the center of the switch, along the arm, up to the lamp on the left-hand side, and down to the other pole of the battery. Now, suppose the arm of the switch is moved to A G, the current will go up as before to the center of the switch, down by the arm, up the wire to the lamp on the right-hand side, and back to the battery by the other wire. In the first case, therefore, the lamp at D lights up, in the second case the lamp at T lights up. The wires from C to D and G to T may be as long as you please, you can therefore control the lamps when they are far apart or in different parts of the house. When the arm of the switch is central neither lamp lights up, or, if you are fitting up the trumpet and drum, the press will not work either when the switch is in this position. This is an advantage, as when people get too inquisitive you can turn off the current, and then whatever they do they will not make the trumpet or drum work till you turn it on again, which you can do when you want them to work for you!

The construction of the switch is so simple that it is hardly necessary to explain the method of joining the wires, but I may say that one is to be joined to the bottom of the brass pillar in the center which supports the brass arm. The others are joined to the right and left terminals, generally by brass screws under the base, but sometimes by screw terminals at the upper surface; this depends on the make of switch which is purchased.

Ingenious readers can easily make a switch for themselves; it only requires a brass arm attached at one end to a central figure, and long enough to touch two screws, or pieces of brass, fixed to the base on opposite sides of it, when turned in their direction. The end of the arm not supported by the brass pillar is provided with a small wooden handle to turn it by.

The switch should be arranged to occupy some dark corner in which you can turn on drum or trumpet to work from the “presses” at will without any one seeing you alter it.

I will only add one thing in conclusion, and that is, that you can have the double wire from the battery and center of switch to the press at the end as long as you like, and it can turn about behind furniture or under the carpet as much as you like, and it will still work instantly from the end press.

Now, by scraping the wire clean at any intermediate point, or as many points as you like, and arranging a simple spring contact fastened to the wires without breaking them so that they can be made to touch when required and spring apart directly the touch is removed (this is easily done with two springs consisting of two strips of sheet brass, one fastened to one wire and one to the other, separated by a piece of wood except at the end when pressed together), you can make the trumpet squeak or the drum roll at any part of the room you like. The springs can be hidden under the carpet so as to be absolutely undiscernible except to the initiated. The best places are under furniture with rather long legs; the foot of the operator can then be placed on the springs, and so make them meet and the trumpet or drum sound without the least chance of detection. The wires not being broken in fixing the springs as described, those springs which are closer to the battery, in no way interfere with those which are further off, as, when these are used, the current simply runs round those that intervene between them and the battery, without being in any way hindered in its course, and the press at the end of the double wire will, therefore, work just as if no intermediate springs existed.

Simple Electrical Experiments.

Frictional electricity is pre-eminently a winter amusement. Not that it is not equally possible to produce the same result in summer, but then other occupations are forced upon us, while in the long winter evenings, with a good fire to dry the air of the sitting-room, the conditions are particularly favorable to electrical phenomena. If a hard frost sets in the conditions will be still more favorable, as this dries the air and the ground outside, while on a wet evening a large fire and warmer room will be needed to produce as good results.

The following experiments are given as a means of amusement to those who know little or nothing of electrical phenomena. Some of them may be recognized by some readers as being standard experiments, others may possess the charm of novelty. To many, however, the whole series will be new, and it is hoped that these will find a new source of interest opened to them, and that they may possibly be impelled thereby to investigate further concerning the causes of what they see. Frictional electrical machines can be purchased from any electrical instrument makers, at a small price, and with these experiments mentioned are more readily performed. In this article I only mention experiments that can be performed with materials to be found in every house, or the necessaries for which can be procured from a shop for a nominal sum. Friction between two substances of any sort probably always produces electricity; but it can only be made visible under certain circumstances.

For instance, if a stick of sealing-wax is warmed and rubbed with a piece of flannel also warm, they both become electrified. This may be proved by holding the wax near an electrometer, which is simply a bottle through the cork of which a wire is passed which has two pieces of gold leaf fastened to its extremity, when the leaves at once diverge owing to the repelling force of the electricity. The flannel is also electrified, but the electricity soon escapes, through the hand of the operator to the ground.

We now proceed to make a simple experiment on the production of electricity on a larger scale. Take a piece of stout brown paper and hold it in front of a hot fire till all the moisture inherent in it is expelled, and the paper is dry and quite hot. Now take it away suddenly, and holding it against the side of the coat rub it briskly with the sleeve by holding the sleeve in the hand. Take it away and hold it against the wall of the room, to which it will instantly adhere firmly, this adherence being caused by the development of electricity over the surface of the brown paper by the friction it has undergone. The paper can be removed from the wall, and on holding it at a short distance will fly towards it and adhere again. In a short time, however, the electricity departs, and the paper falls to the ground. If the hand is spread open upon the paper as it sticks, the electricity departs at once and the paper falls. A spark can be obtained from the paper, but it is hardly strong enough to be visible. In the next experiment, however, it is plainly to be seen.

Take an ordinary tea-tray and place it on the top of four glass tumblers, which must have previously been made quite hot and dry at the fire. They must also be scrupulously clean, as dirt is a good conductor of electricity. Now take a sheet of foolscap paper, and heat it strongly at the fire until perfectly dry, as the brown paper was. Place it while hot flat on the table and rub it from side to side, from the top to the bottom, with a piece of thick india-rubber. It will now adhere firmly to the table on account of the electricity developed. Take hold of two corners, pull it up, and quickly place it on the tray. On approaching the knuckle of your closed hand to the edge of the tray you will now obtain a brilliant spark, which, if the room is dark, will appear vivid. On removing the paper from the tray, and again approaching the knuckle, another spark will pass, but not so bright as the former. The experiment can be repeated as often as wished by heating and rubbing the paper again.

Now take four more tumblers, heat them as before, and place them on the floor with a board on the top of them. Let someone stand on this board, taking care that he is completely separated from all surrounding objects of furniture, etc., and that his clothes do not touch the table while the experiment is performed. Let him place his hand on the tray while the paper is heated, rubbed, and placed thereon.

He will then become charged with electricity, and if he approaches his hand to any one else’s a spark will pass between them. (This should not be done with susceptible parts of the body, the eyes for example, as it would be rather painful.) Let some one be provided with a spoon in which a little methylated spirit is heated; if the charged person holds his knuckle to this spirit it will instantly be ignited. Small pieces of paper—comic paper figures, etc.—will dance up and down briskly if he holds his hand outspread over them while lying on the table. The same thing will happen if the pieces of paper are placed between the tray and the table when the former is charged by the hot paper, or if the brown paper in the first experiment is held above them when excited.

Now take a needle and place it on the tray, its point projecting over the edge. If the room is now darkened, on placing the excited paper on the tray, the point of the needle will be seen to glow brilliantly for some seconds. This is caused by the electricity escaping into the air from the point of the needle, and is known as the “brush discharge.” The tray will consequently speedily lose its electricity. It will be found to be impossible to get a spark from the tray as long as the needle is on it, as the electricity vastly prefers to escape by the point. The escape of the electricity may be rendered still more evident by means of the following piece of apparatus.

Take two pieces of thin wire about two inches long, and bend each at right angles about an eighth of an inch from each end, both the bent portions being in the same direction. These two pieces of wire are now to be joined together at the middle at right angles by means of a piece of finer wire twisted around them. This finer wire can, with a little care, be caused to form a small cap, in which the point of a needle is inserted, the needle acting as a pivot, so that the bent wires turn freely on top of it (Fig. 1). The needle is supported by thrusting it into a large cork to act as a stand.

A fine wire is then twisted several times around the bottom of the needle, and the whole apparatus is then placed on the tray, the end of the wire attached to the needle being carefully arranged so as to touch the tray, a metallic connection with the tray being essential to success. If the needle can be soldered to a metal stand, or the cork covered with tinfoil, the wire is not needed. On rubbing the paper and placing it on the tray, the electricity passes up the wire into the needle, thence into the wire cross, and escapes by the bent portions of the wires, each of which should be filed to a point. In escaping it electrifies the surrounding air, and this, according to the law that “like electricities repel each other,” has a reacting force on the wire arms. Accordingly the windmill begins to turn, and may attain a tolerable rate of speed if the tray is strongly charged.

Another amusing experiment is that known as the “electrical head of hair.” The head of a wooden doll is taken, and either provided with a real head of hair, which must be combed out straight, or a quantity of cotton is fastened to it to resemble hair.

If the head is fastened to a metal stand, and placed on the tray when the excited paper is laid upon it, the hairs become charged, and consequently repel each other, causing the whole head of hair to stand erect, each hair separate from the rest, thus presenting a most remarkable appearance. For the same reason, if a heap of small pieces of paper, feathers, etc., is laid on the tray, on placing upon it the electrified paper they will jump off in all directions, each being repelled by the others, in the same way as the gold leaves of the electroscope were repelled in the first experiment. If two pieces of pith are suspended by silk threads to a support, so as to hang close to each other, on bringing near them the electrified wax or tray they will be charged and will repel each other for some time. If when charged by the wax a heated glass rod rubbed with silk is brought near to them, they will fly to it, instead of retreating. This seems to indicate a difference between the electricities of the wax and the glass, the former of which has therefore been called negative, and the latter positive.

For giving stronger shocks than the tray is capable of, we may have recourse to the apparatus known as the Leyden jar, which may be easily charged by means of the tray and excited paper. A Leyden jar is thus easily and cheaply constructed: Take an ordinary wide-mouthed pickle bottle and a cork to fit it. Cover the outside with tinfoil, which can be fastened on with gum, and should be laid on as smoothly and as free from creases as possible. Tinfoil can be procured from any chemist. The outside being finished, the inside has to be covered also, which is a work of greater difficulty. It can best be performed by cutting another piece not quite so large as that on the outside of the bottle but of the same shape, and passing into the bottle without creasing it more than can be helped, it can be arranged inside the bottle so as to fit smoothly all round. Now a piece of brass wire is to be passed through the cork, at the end of which is a brass knob, or if simply bent round it will work, though the knob is neater. At the end of the wire which is inside the bottle a brass chain is fastened so as to touch the tinfoil inside the bottle when the cork is inserted. The tinfoil inside and outside the bottle must only reach to the bottom of the neck, leaving a space between it and the cork.

The Leyden jar is now complete, and must be thoroughly warmed before charging it. When quite hot it can be charged by bringing the knob (the jar being held by the outer coating of tinfoil) near the tray, when the excited paper is laid upon it. A spark will pass between the tray and the knob, and this must be repeated several times (say twenty for a first experiment), the jar being charged more fully the more sparks are put into it. Any one now taking the jar in one hand by the outer coating and placing a finger of the other hand near the knob will receive a shock, the severity of which depends on the number of sparks put into the jar. Several people can take the shock by joining hands, the outside one on one side holding the jar, and the outside one on the other side touching the knob. Those in the middle will not feel the shock quite so strongly as those on the outside.

This is an example of the “quick discharge” of a Leyden jar. It can, however, also be discharged slowly, and the following experiment makes use of this faculty. Take three small bells, which can be procured at any toy shop, and remove the clappers. Now suspend two of them by wires at opposite ends of a piece of metal or stout wire about three inches long, and suspend this wire in the center by a bent wire (or wooden, if covered with tinfoil) support, which is fixed to a thick piece of board, covered with tinfoil, to act as a base.

The tinfoil must be in communication with the supporting wire, and the height of the bells must be so adjusted that when the Leyden jar is placed between them with the third bell supported on the knob (the support of the clapper will have to be removed from the bell for this purpose), all three bells will be of equal heights and about half an inch distant from each other. (The diagram Fig. 2 will explain the arrangement.) Now suspend two small brass buttons by silk threads so as to hang between the bells when the Leyden jar is placed in the center. Charge the jar with the tray and replace it in position (of course with the bell on the top); the buttons will then begin to move backwards and forwards between the bells, and the latter will keep up a vigorous chiming until the electricity of the jar is exhausted. In this experiment it is essential that the supports be of metal, or wood covered with tinfoil, as the electricity passes from the inside of the jar to the outside while it is standing upon the tinfoil, by means of the balls, and thus causes them to vibrate.

A candle which has just been blown out, leaving the wick glowing, can easily be lighted by means of the charged Leyden jar if a piece of bent wire is held touching the outer coating and the other end on one side of the wick while the knob is approached to the other, so that the spark passes through the glowing wick. In the same way spirits of wine can be lighted, and gunpowder, guncotton, etc., exploded. To do this, it is best to have two pieces of bent wire provided with handles of glass at the middle. These wires are held by the handles, one in contact with the outer coating, and the other with the inner coating, of the charged Leyden jar. On approaching the other two ends of the wires a spark passes between them, and if a small quantity of gunpowder is placed on a table and the spark is made to pass through it by approaching the wire to either side it will be fired.

There are many other experiments which can be performed by the help of the simple apparatus described, but it would take up too much space to describe them.

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3. Little Lou, the Pride of the Continental Army. A Story of the American Revolution by General Jas. A. Gordon
4. Railroad Ralph, the Boy Engineer by Jas. C. Merritt
5. The Boy Pilot of Lake Michigan by Capt. Thos. H. Wilson
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7. The Little Swamp Fox. A Tale of General Marion and His Men by General Jas. A. Gordon
8. Young Grizzly Adams, the Wild Beast Tamer. A True Story of Circus Life by Hal Standish
9. North Pole Nat; or, The Secret of the Frozen Deep by Capt. Thos. H. Wilson
10. Little Deadshot, the Pride of the Trappers by An Old Scout
11. Liberty Hose; or, The Pride of Plattsville by Ex Fire Chief Warden
12. Engineer Steve, the Prince of the Rail by Jas. C. Merritt
13. Whistling Walt the Champion Spy. A Story of the American Revolution by General Jas. A. Gordon
14. Lost in the Air; or, Over Land and Sea by Allyn Draper
15. The Little Demon; or, Plotting Against the Czar by Howard Austin
16. Fred Farrell, the Barkeeper’s Son by Jno. B. Dowd
17. Slippery Steve, the Cunning Spy of the Revolution by General Jas. A. Gordon
18. Fred Flame, the Hero of Greystone No. 1 by Ex Fire Chief Warden
19. Harry Dare; or, A New York Boy in the Navy by Col. Ralph Fenton
20. Jack Quick, the Boy Engineer by Jas. C. Merritt
21. Doublequick, the King Harpooner; or, The Wonder of the Whalers by Capt. Thos. H. Wilson
22. Rattling Rube, the Jolly Scout and Spy. A Story of the Revolution by General Jas. A. Gordon
23. In the Czar’s Service; or Dick Sherman in Russia by Howard Austin
24. Ben o’ the Bowl; or The Road to Ruin by Jno. B. Dowd
25. Kit Carson, the King of Scouts by an Old Scout
26. The School Boy Explorers, or Among the Ruins of Yucatan by Howard Austin
27. The Wide Awakes; or, Burke Halliday, the Pride of the Volunteers by Ex Fire Chief Warden
28. The Frozen Deep; or, Two Years in the Ice by Capt. Thos. H. Wilson
29. The Swamp Rats; or, The Boys Who Fought for Washington by Gen. Jas. A. Gordon
30. Around the World on Cheek by Howard Austin
31. Bushwhacker Ben; or, The Union Boys of Tennessee by Col. Ralph Fenton

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