simple contact. If electricity be made to pass through the prepared limb by the immediate contact of the electrified body, a much smaller quantity of it is sufficient to occasion the contractions, than when it is made to pass from one conductor to another, at a certain distance from the prepared limb; and these contractions are much stronger, when the electricity passes through a nerve to the muscles, than through any other part. Similar effects may be produced in the prepared animal, without any apparent aid of electricity, merely by making a communication between the nerves and muscles by a conducting substance. But if the communication between the nerve and the muscle be formed by substances which are non-conductors of electricity, as glass, sealing-wax, &c. then no contractions take place.

The conducting substances, which answer best for this purpose, are silver and zinc; but silver and tin, or silver and copper, will answer very well. If part of the nerve of a prepared limb be wrapped up in a piece of tin-foil, or be laid upon zinc, and a piece of silver be laid with one end on the muscle, and with the other upon the tin or zinc, the contractions of the limb will be violent.

Let

The two metals may be placed either in contact with the preparation, or in any other part of the circuit, which may be completed by means of other conductors, as water. two wine-glasses, nearly full of water, be near to, but not actually touching each other. Put the prepared thigh and leg of a frog into the water of one glass, and laying the nerve over the edges of the two glasses, let the tin-foil, which is wrapped round it, touch the water of the other glass. If now a communication be formed between the water in the two glasses, by means of silver, or by putting the fingers of one hand into the water of the glass that contains the leg, and holding a piece of silver in the other, the coating of the nerves being touched with it, the prepared legs will be so much excited as sometimes actually to jump out of the glass. These contractions may be excited in living as well as in dead animals,

Take, for instance, a live flounder, and having made it dry, put it in a pewter-plate, or upon a large piece of tin-foil, and place a piece of silver on its back; then with one end of a piece of metal touch the pewter-plate, and apply the other extremity of the metal to the silver, and contractions will immediately ensue.

Experiments of a similar kind, which are recorded by Aldani and others, were made upon many different kinds of animals, and even upon persons who had suffered death from the hands of the executioner; the actions produced were ascribed to a principle of electricity, and the science, then only in its infancy, thus limited to general experiments on the animal frame, was denominated, after its earliest discoverer, Galvanism.

Galvani explained the phenomenon, by conceiving the muscles to resemble a charged Leyden phial, having electricity accumulated in the inside, while the outside was charged minus. The nerves he considered to be connected with the inside when it was united with the outside by conductors, the surplus electricity was discharged, which caused the motions of the limb.

Signior Volta, the illustrious improver of this science, set out with the idea, contrary to that of Galvani, that the electricity did not belong to the animal, but to the different metals employed. Galvani was not likely to produce any greater effect than what could be obtained by two pieces of metal, because he believed the electricity to be in the animal. Volta was led to the discovery of the battery by combining a number of pieces of metal together, because he was persuaded that the electricity was in the metals or fluids employed. These repeated combinations obtained the name of Galvanic, or more properly, Voltaic batteries, and the science itself is usually denominated from the discoveries resulting from these batteries, Voltaism.

VOLTAISM.

THE batteries of Volta are said to be of the first or second order, according as the simple combinations of which they consist, are of the first or second order. The batteries of the first order are composed of two perfect conductors, and one imperfect conductor, as zinc with gold, or silver, or copper, &c. and a solution of nitric acid in water.

The batteries of the second order, are composed of two imperfect conductors and one perfect conductor, as one metal with two fluids.

In Plate IV. fig. 5, we have the representation of a voltaic battery. It consists of a number of pieces of silver, zinc, and flannel cloth, of equal sizes; the flannel is moistened with an oxydating fluid, and they are so arranged that the zinc, silver, and flannel, may succeed each other in regular order as often as the combinations are repeated. If the lower piece of metal is touched with one hand, and the upper one with the other, an electrical shock will be felt. The same experiment may be repeated till the metals become, in a measure, oxydated and unfit for action, when they must be taken down and cleaned.

In fig. 6 is a different kind of battery, in these four glasses, and twenty or more might be used, in order that the effect might be more powerful, is a solution of salt and water: into each, except the two outer ones, is plunged a small plate of zinc, and another of silver, these communicate with each other by a thin wire, so fastened 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. If one hand be now dipped into the first glass, and the other into the last, there will be made a communication between the zinc and silver, and a shock will be felt.

Another and more powerful kind of battery, consists of a trough of baked wood three inches deep, and as many in breadth, fig. 7. In the sides of this trough are grooves opposite to each

other, and about a quarter of an inch asunder. Into each pair of grooves is put a plate of zinc, and another of silver, and they are cemented in such a manner as to prevent a communication between the different cells. The cells are now filled with some oxydating fluid, and the battery is complete; if a communication be made with the two hands between the two end cells, a strong shock will be felt. With batteries of this kind, only much increased in size, a number of curious and interesting experiments may be made. Wire may be melted, and gunpowder, gold and silver leaf, &c., may be inflamed. Water has also been decomposed by means of batteries of this kind; let AB, fig. 8, represent a glass tube filled with distilled water, having a cork at each end. A and B are two pieces of brass wire, which are brought within about an inch of one another in the tube, and the other ends are carried to the battery, viz. A to the positive and B to the negative end; when, if the battery be in full action, and the circuit be uninterrupted, a stream of bubbles will proceed from the wire B, and ascend to the upper part of the tube: these bubbles are hydrogen gas, or inflammable air, and they no doubt proceed from the water, being one of the component parts of it. The experiment, as described in several books, may be varied, and both the oxygen and hydrogen gas collected separately.

In the hands of Sir Humphry Davy, the Voltaic battery has achieved the most important and interesting discoveries, which the student in natural philosophy will take much pleasure in examining for himself in the papers of that great chemist, to be found in the different volumes of the Transactions of the Royal Society since the year 1806; in the course of which he proves most satisfactorily, that the voltaic energy has the property of decomposing all compound substances, provided the battery be sufficiently powerful, and the constituents of such compound bodies will range themselves about the wires that pass from the extremities of the batteries, according to the following law : oxygen and acids arrange themselves about the positive wire, being themselves possessed of negative qualities: while hydro

gen, alkalies, earths, and metals, being possessed of positive qualities, are attracted naturally to the negative wire.

Hence it is inferred, that when two substances are chemically combined, they are in different states of electricity; and the more completely opposite these states, the more intimately will they unite. Thus water is an instance of the complete chemical combination of the negative oxygen and positive hydrogen gases: and to separate the two constituents from each other, we have, as we have seen, only to bring them to the same electrical state, and this effect the voltaic energy produces; which fact is supposed to prove that chemical affinity, that most important law in nature, is nothing more than the attraction which exists between bodies in different states of electricity. See Chemistry.

The decomposition of the fixed alkalies, of the alkaline earths, of boracic acid, and other substances, of which very interesting and detailed accounts are given in the papers above referred to, was discovered by Sir Humphry Davy, and the result of his original discovery. "These facts, though very striking and important, are not to be compared, in point of value, to his original discovery of the principle, the decomposing power of Voltaism, which has made us acquainted with a new energy in nature, and put into our possession a much more efficient chemical agent than any with which we were before acquainted. This is the discovery which does so much honour to Sir Humphry Davy, and has put him on a level with the small number of individuals who have been fortunate enough to lay open to the world a new law of nature."

The first grand experiment upon the igniting powers of large voltaic plates formed into batteries, was made by the French chemists, Fourcroy, Vauquelin, and Thenard; but a much larger combination for exhibiting the effects of an extensive surface was constructed by Mr. Children; it consisted of a battery of twenty double plates four feet by two, of which the whole surfaces are exposed, in a wooden trough, in cells covered with cement, to the action of diluted acids. The