GALVANISM, this surprising branch of philosophy has been denominated gal vanism, from Galvani, an Italian professor, whose experiments led to its discovery.
In 1789, some time before he made the most important discovery, he was by ac cident led to the fact, of electricity hav ing the property of exciting contractions in the muscles of animals. Stimulated by the then prevailing idea of electricity being a principal inherent in animals, which, acting upon the muscular suscep tibility, was the immediate cause of mus lar motion, he was induced to persevere in the inquiry, during the prosecution of which he brought to light other facts, which laid the foundation of this valuable scientific acquisition.
After having observed that common electricity, even that of lightning, pro duced vivid convulsions in the limbs of recently killed animals,he ascertained that metallic substances, by mere contact, un der particular circumstances, excited si milar commotions.
He found that it was essential, that the forces of metals employed should be of different kinds. He applied one piece of metal to the nerve of the part, and the other to the muscle, and afterwards con nected the metals, either by bringing them together, or by connecting them by an arch of a metallic substance ; every time this connection was formed, the con vulsions took place. The diversity in the metals employed in these experiments appeared, in the very early stages of this I, inquiry, to be connected with their re , spective degrees of oxydability, the one , being possessed of that property in a I great degree, and the other little liable ' to the change. Hence zinc, and silver, or gold, was found to produce the great est muscular contractions. The experiments of Galvani were con firmed by many able philosophers, by I whom they were repeated. Those who particularly distinguished themselves by their labours on this subject were, Valli, Volta, Drs. lilonro and Fowler. , Galvani had theorised upon the pheno inena which he had observed to a consi, derable extent. He conceived, that the convulsions were produced by a disturb ance of the electricity inherent in aM mals, which was identical with the ner vous fluid, and that the metallic substan ces employed had not any other effect, than that of transmitting the electricity from the nerve to the muscles producing the contractions in question.
Simon Volta, with much labour and in genuity, successfully opposed the hypo thesis of Galvani. He had recourse to those valuable experiments made by Ben net, by which to explain the phenomena observed by Galvani. Bennet had some time before observed, when plates of dif ferent metals were brought in contact, that one of the metals transmitted a por tion of its electricity to the other, each of which, when separated, being at the same time insulated, evinced signs of contrary states of electricity. When the plates, for instance, were one of copper and the other zinc, the former, while the two were in contact, gave a portion of its electricity to the latter. Hence, when they were separated, and thus presented to the electrometer, the copper exhibited signs of negative electricity, and the zinc that of positive.
On this ground it was that Volta object ed to the hypothesis of Galvani, and esta. blished the more plausible idea, that the electricity was furnished by the disturb ance of that fluid, arising from the con tact of the different metals, and that the convulsions were excited by the stimulat ing effect of that active agent. It was in the investigation-of this experiment, that this truly ingenious philosopher was led to the discoveryof the pile, which,from its inventor, has been called the Voltaic pile. This apparatus consisted, in combining the effects of a number of pairs of the dif ferent metals, and by that means constitut ing a battery in galvanism, similar in effect to the Leyden phial in common electricity.
As silver and zinc had been found in the minor experiments to produce the greatest effect, these metals were employ ed by Volta in the construction °Phis bat tery. The silver plates generally consisted of coins ; and the zinc plates were of the same size, being frequently cast in moulds made with the silver. The same number of pieces of cloth, pasteboard, or leather, of the same size, and steeped in solution of common salt, were also provided. The above substances were formed into a pile, in the following order : zinc, silver, wet cloth ; zinc, silver, wet cloth ; and so on, in the same order, till the pile became sufficiently high. If it were to be elevat ed to any considerable height, it was usual to support it on the sides with three pil lars of glass, or varnished wood.