Get two round pieces of wood, A B, and coat them with tinfoil; or two pieces of metal plate; attach one of them to the prime conductor by a chain, and let it hang about two or three inches from the k.n.o.b. Place some pith-b.a.l.l.s upon the bottom piece of wood B, and bring it under the other. Immediately this is done, and the upper piece is charged with electricity from the machine, the pith-b.a.l.l.s will jump up and down, and from one to the other with great rapidity. If some of the pith be formed into little figures, they will also dance and leap about in the most grotesque manner. The same may be made to dance by merely holding the inside of a dry gla.s.s tumbler to the prime conductor for a few minutes, while the machine is in action, and then if this be placed over them they will jump about, to the astonishment of the spectators, as the cause of their motions is not quite so apparent.

THE ELECTRICAL KISS.

This amusing experiment is performed by means of the electrical stool.

Let any lady challenge a gentleman not acquainted with the experiment to favour her with a salute. The lady thereupon mounts the gla.s.s stool, and takes hold of a chain connected with the prime conductor. The machine being then put in motion the gentleman approaches the lady, and immediately he attempts to imprint the seal of soft affection upon her coral lips, a spark will fly in his face, which generally deters him from his rash and wicked intention.

RINGING BELLS.

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Bells may be made to ring by electricity in the following manner. Let three small bells be suspended from a bra.s.s wire, D D, and supported by a gla.s.s pillar A, pa.s.sing through bell B to the bell E. The electrical apparatus being attached to the k.n.o.b F, the electricity pa.s.ses down the wires D D to the bells, which are then positively electrified and attract the clappers C C, that are negatively so, in consequence of being insulated by the silken strings, which are not conductors. The bells therefore attract the clappers till they are charged, when they strike against the centre bell to discharge themselves, and thus a peal is rung on the bells until the electricity is driven off.

WORKING POWER OF ELECTRICITY.

This may be shown in a variety of ways. The subjoined machine will exhibit the principle upon which many ingenious toys may be made by the young philosopher. In the figure A is a wooden board or stand, B B B B, four pillars of gla.s.s, gutta-percha, or sealing-wax, having fine wires, C C, stretched above. On these rest the rotatory wire or wheel F, having its points turned the reverse ways. By means of a chain attached to the conductor, and to the instrument at B, the electricity pa.s.ses over the pillar B, up the wire C into the wheel, and off at the points, which causes it to be turned round on an inclined plane till it reaches the top.

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THE ELECTRIFIED WIG.

While a person is on the electrical stool, if he be charged with much electricity,

"Each hair will stand on end, Like quills upon the fretful porcupine."

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A wooden head--not your own, but a real wooden head--with a wig of streaming hair, and a handsome face to correspond, may be made in the following form, with a wire in the neck to support it by, and fixed in the conductor of an electrical machine. When this is put in motion the hair will rise up, as in the figure, in a manner to astonish even the "big-wigs."

IMITATION THUNDERCLOUDS.

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To show the manner in which thunderclouds perform their operations in the air, A A is a wooden stand, on which are erected two uprights, B B; C C are two small pulleys, over which a silken cord can pull easily; E is another silken line stretched across from one upright to another; on these silken cords two pieces of thin cardboard covered with tinfoil, and cut so as to represent clouds, are to be fixed horizontally, and made to communicate, by means of thin wires F and G, one with the _inside_, and the other with the _outside_, of a charged jar, D. Now, by pulling the loop of the silk line, the clouds will be brought near the cloud 2; continue this slowly, until the clouds (which are furnished with two small bra.s.s b.a.l.l.s) are within an inch of each other, when a beautiful flash, strongly resembling lightning in miniature, will pa.s.s from one cloud to the other, restoring electrical equilibrium.

THE LIGHTNING STROKE IMITATED.

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If the jar D be put behind the stand, and the cloud 2 removed, a vessel communicating by means of a wire with the outside of the jar may be swum in water under the remaining cloud; the mast being made of two pieces, and but slightly joined together, with a hollow s.p.a.ce in one half of the mast, into which the ends of the conductor pa.s.s, but do not touch, leaving an interval of about a quarter of an inch between them. The hollow is then filled with gun-cotton, and closed with cork. When the cloud is pa.s.sed over the vessel, the mast will be struck and shattered to pieces. A strip of tinfoil, arranged with pins over the hollow part of the mast, will show how a continuous conductor will convey the discharge safely away.

THE SPORTSMAN.

This apparatus is capable of affording much amus.e.m.e.nt. A is a stand of wood, B is a common Leyden jar, out of which proceed the wires H H--one terminating in ball F, the other in the ball D--to which are attached a number of pith birds by silken strings; E is a shelf for the birds to rest upon; C is the sportsman; G his gun.

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To put this operation in motion the Leyden jar is to be charged with electricity by affixing a chain to the bottom part of it, and connecting it with an electrical machine in the usual manner, or by applying it to a prime conductor, when the birds will fly off the k.n.o.b to which they are fixed in consequence of their being repelled. If the sportsman and gun be then turned, so that the end of his gun shall touch the k.n.o.b F, an electric spark will pa.s.s from one to the other, a report will be heard, and the birds will fall down as if shot, in consequence of the electricity having been taken from the Leyden jar. There should be a communication between the sportsman and the jar formed of tinfoil, or some metal, as shown by the dotted line on the stand.

Such are a few of many numerous experiments which may be made by the young experimenter, who is fond of science and has any ingenuity; but should he like to amuse himself with an electrifying machine of little cost, he may warm a sheet of brown paper, and then rub it briskly on a teatray with india-rubber; on raising the paper in a dark room, he will see many pretty electrical sparks.

The back of a black tom cat is sometimes recommended as a cheap electrical machine; but as the wishes of the animal have to be consulted, perhaps it is wiser to leave the cat alone.

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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 quant.i.ty, 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 circ.u.mstances.

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 crown and place it on the top of his tongue, and place a half-crown underneath it, and bring the edges of the half-crown 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.

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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 pa.s.ses 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 quant.i.ty 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 gla.s.ses and the number of the pieces of metal. If we take six such gla.s.ses 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 gla.s.s to gla.s.s 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 gla.s.s 1 is connected with the zinc of gla.s.s 2, and so on.

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TO MAKE A MAGNET BY THE VOLTAIC CURRENT.

To effect this, make a connexion 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 pa.s.sed 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 pa.s.s along a wire under which, and in a line with it, a compa.s.s 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.