These batteries may be constructed in an infinite variety of forms. We shall describe those that have been as yet most generally used.

The apparatus of Volta was constructed in the following manner : Take a number of plates of copper, or, what is better, of silver, and an equal number of tin plates, or, what is still better, of zinc, and the same number of pieces of card, leather, or woollen cloth, the last of which seems to answer the best. Let these last be well soaked in common water, or rather in a solution of common salt, sal ammoniac, nitre, or nitrous acid. The silver, or copper, may be pieces of money, and the zinc pieces may be cast of the same size. A pile is to be formed of these substances in the following manner: a piece of zinc, a piece of sil- ' ver, and a piece of wet cloth, or card; then another piece of zinc, a piece of silver, and a piece of wet cloth; and so on in the same order, till the number required has been placed. The instrument is then fit for use; but as the pieces, when unsupported, are apt to fall down when their number is considerable, it is best to support them by means of three rods of glass, stuck into a piece of wood, and touching the metallic pieces at three equally distant points, as represented in Fig. 7. Down these rods may slide a small circular piece of wood, having three holes in it, and which will serve to keep the top of the pile tight, and the different pieces in close contact. The moistened pieces should likewise be somewhat less than the pieces of metal, and though they should be well moistened, they should be gently squeezed before they are applied, that the superfluous moisture may not run down the pile, or insinuate itself between the pieces of metal.

The instrument, constructed in this manner, will afford a perpetual current of the electric fluid, through any conductor communicating between the uppermost and lowest plate: and if one hand be applied to the lowest plate, and the other to the upper, a shock is felt, which is repeated as often as the contact is renewed. The principal objections to this construction of the pile, or battery, is the trouble of placing the pieces in the proper order, and also that of cleaning the pieces of zinc, which are rapidly oxydated. The best method of doing this, is by a file, or by putting them into diluted muriatic acid, which dissolves the oxyd.

The battery, Fig. 8, consists of a row of wine glasses, or cups, containing salt and water, or nitrous acid and water. Into each of these is plunged a plate of zinc, and another of silver. These plates are made to communicate with each other by means of a thin wire, fastened so that the silver of the first glass is connected with the zinc of the second, the silver of the second with the zinc of the third, and so on progressively through the whole chain of glasses. When one hand is dipped into the first glass, and another into the last, the shock is perceived.

But though this machine will continue in action a very long time, and when the pieces of zinc are oxydated, they may be easily taken out and cleaned; yet it occupies a great deal of room, when an apparatus of considerable power is wanted.

The battery represented in Fig. 9, is found much more convenient, not being liable to the objections of the two last. It consists of a trough of baked wood, about three inches deep, and about as broad. In the sides of this vessel are grooves opposite to each other, and about a quarter of an inch apart. Into each pair of these opposite grooves is

put a plate of zinc and silver, or zinc and copper soldered together.. These plates are well fixed in the grooves, in the proper order of silver and zinc, silver and zinc, as in the pile, by a cement made of five parts of resin, four of bees-wax, and two parts of powdered red ochre. This cement must be run in very carefully, so as absolutely to prevent any communication between the different cells, which would entirely prevent the action of the machine. The cells are then filled with water containing a little acid, common salt, or muriate of ammonia.

When a communication is made between the first and last cell, by means of the hands, a strong shock is felt.

Instead of silver, or copper and zinc, any of the above-mentioned combinations will answer.

The action of all these batteries is greatest, when they are first completed, or filled with the fluid; and it declines in proportion as the metal is oxydated, or the fluid loses its power. Hence, after a certain time, not only the fluid must be changed, but the metallic pieces must be cleaned by removing the oxydated surface, which is done either by filing or by rubbing them with sand-paper, or by weak muriatic acid, which dissolves the oxyd.

When a galvanic battery of the first order (the action of those of the second order being weaker, and much more transient), consists of twenty repetitions of simple combinations, if you touch with one hand one extremity of the battery, and apply your other hand to the other extremity, you will feel a very slight shock, like that which is communicated by a Leyden phial weakly charged, and it will be hardly felt beyond the fingers, or at most the wrists. This shock is felt as often as you renew the contact. If you continue your hands in contact with the extremities, you will perceive a slight but continued irritation; and when the hand, or the other part of the body which touches the other extremity of the battery, is excoriated or wounded, this sensation is disagreeable, and rather painful.

The intensity of the charge is, however, so low, that it cannot make its way through the dry skin of the hand, which is but an imperfect conductor: the fingers should therefore be well moistened with water. It will be better to immerse a wire that proceeds from one extremity of the battery in a bason of water, wherein you may plunge one of your hands; then grasping with your other hand well moistened a large piece of metal, for instance a large silver spoon, touch the other end of the battery with it, and the shock will be felt more distinctly.

Several persons may receive the shock together, by joining hands in the same manner as in receiving the shock from a Leyden phial. For this purpose, the hands must be well moistened with water. But the strength of the shock is much diminished by passing through so long a circuit, the last person feeling it much less violently than the first. In general, its effect is lessened by passing through imperfect conductors.

The galvanic shock is similar to that from a common electrical battery weakly charged, and not like a small Leyden phial fully charged. The difference appears to consist in this, that the latter contains a small quantity of the electric fluid much condensed, so that it can force its way through a certain distance, perhaps an inch of air; but the former contains a vast quantity of the electric fluid, in a very rare, or little condensed state: it cannot, therefore, force a passage through the air,

and the substances that form the communication must come into actual contact, or very nearly so. Thus a discharge of a very powerful battery will not take place, if the wires forming the communication be more than a fortieth of an inch apart.

It appears very probable, that a galvanic battery pats into action a great quantity of the electric fluid, in a state little condensed. From the circumstance of the substances of which the pile is composed being all good conductors of electricity, it would appear, that the electric fluid in a galvanic battery cannot be in a very condensed state, otherwise it would easily pass from one end to the other, and restore the equilibrium. And, indeed, it is not easy to be conceived why this does not always happen.

In this case a small but very vivid spark is seen at the points of the wires, accompanied with a pretty loud snapping noise. There is no perceptible difference of appearance between the spark of the positive, and that of the negative end of the battery.

If a wire proceeding from one extremity of a pretty strong galvanic battery, be made to communicate with the inside coating of a common large jar, or electrical battery, and a wire which proceeds from the other extremity be made to communicate with the outside coating : the latter will become weakly, but almost instantaneously, charged, in the same manner as if it had been charged by a few turns of a common electrical machine; and with that charge you may produce the same effects as by an equal quantity of common electricity.

The shock from a battery consisting of 50 or 60 pairs of zinc and silver, or zinc and copper, may be felt as far as the elbows: and the combined force of five or six such batteries will give a shock that few men would be willing to receive. The prepared limbs of a frog, or other animal, are violently convulsed, but soon exhausted of their irritability by the action of this battery.

The spark from a galvanic battery acts with astonishing activity upon inflammable bodies when sent through them. It fires gunpowder, ether, spirit of wine, cotton, hydrogene gas, phosphorus, &c. it renders red hot, fuses, and consumes very slender metallic wires, and metallic leaves, as tin-foil, gold, silver, and brass-leaf. The method of making these experiments is as follows: having filled the cells of the battery (Fig. 9.) with water containing a little nitrous acid (about one-tenth of acid will form a very active fluid), wipe carefully the edges of the plates with a towel, to prevent any communication between the cells. Having fastened bits of copper to the ends of two pieces of wire, as Fig. 10, of which annealed copper wire is the best, insert them into the fluid in each of the extreme cells, as in Fig. 9. Upon the other ends of the wires, slip on a bit of small glass tube to lay hold of the wires by. After a few minutes the acid will act upon the plates; and if the points of the wires be brought near to each other by moving them by the glass tubes, a spark will be perceived between them. Some of the inflammable substance intended to be acted upon may be laid upon a plate of glass, or put between the points of the wires. In this manner the combustion of gold and silver leaf, &c. may be shewn, forming some of the most beautiful experiments that have ever been exhibited. Copper or brass leaf, commonly called Dutch gold, burns with a beautiful green light, silver with pale blue light, and gold with yellow light, and all

with a crackling something analogous to the noise heard in the burning of paper rubbed over with wet gun-powder.

When very great power is wanted, several of these batteries may be united, by placing them together, as in Fig. 11. Pieces of copper are cut into the form shewn by Fig. 12, and bent as in Fig. 13: the bent ends of these pieces being inserted into the adjoining cells, at the extremities of each battery, a communication is formed from the end A of the first battery, to the end B of the last battery. If wires be now placed in these ends, in the same manner as in the battery Fig. 9, the collected force of the whole will be exhibited at the points of the wires.

It is usual to make these batteries with 50 pairs of metallic plates in each, so that four batteries contain 200 pairs of plates, which are sufficient to produce all the effects above-mentioned in the most satisfactory manner. Two of these batteries will, if properly prepared, exhibit most of the usual experiments.

One of the most extraordinary effects of the galvanic pile or battery, is the apparent decomposition of water. Fill a small glass tube with distilled water, and fitting a cork to each extremity, as in Fig. 14, make a piece of brass or copper wire pass through each of the corks into the water. Connect then the wire A with one of the extremities of the battery, while the wire B communicates with the other extremity. You will then find, that minute bubbles of gas proceed in a constant stream from the end of the wire which passes from the negative end of the battery, and ascending to the upper part of the tube, accumulate by degrees. This gas, if examined, will be found to be hydrogene, and may be inflamed by the approach of an ignited body on pulling out the cork. At the same time the other wire deposits a stream of oxyd in the form of a cloud, which gradually accumulates on the sides and bottom on the tube. If you interrupt the circuit, the streams of gas and oxyd disappear, but are renewed again upon restoring the communication.

In this experiment it would appear, that the hydrogene is separated from the water, and is converted into a gaseous state by the wire connected with the negative extremity of the battery: whilst the oxygene unites with, and oxydates the wire connected with the positive end of the battery. If you connect the positive end of the battery with the lower wire of the tube, and the negative with the upper, then the hy drogene proceeds from the upper wire, and the lower wire is oxydated.

If two wires of gold or platina be used, which are not oxydable, then the streams of gas issue from each, the water is diminished, and the collected gas is found to be a mixture of hydrogene and oxygene, and explodes violently on the approach of an ignited body, or by the electric or the galvanic shock."

To obtain these gases separately, let the two ends of the gold wires be immersed in a vessel of water (Fig. 15), and be about one inch apart. Then hang over them two wine-glasses, inverted, and full of water. The gases will then ascend into the separate vessels.

It is well known that hydrogene gas, in its nascent state, reduces the oxyds of metals. Accordingly, when the tube (Fig. 14) is filled with a solution of acetite of lead in distilled water, and a communication is made with the battery as above described, no gas is perceived to issue from the wire which proceeds from the negative end of the battery; but in a few minutes, beautiful metallic needles are perceived on the