Galvanism. Galvanism is so intimately connected with electricity, that it may be considered as a branch of that science. It was first accidentally discovered in the chemical laboratory of M. Lewis Galvani, pro-fessor of anatomy in the university of Bologna, upon the following occasion : The lady of the professor being of a delicate habit, was occasionally supported by soup made from frogs as a restorative. Some of these animals, skinned for that purpose, were lying upon a table in the laboratory of the professor, in which stood an electrical machine. One of the assistants, in experiment, by accident brought the point of the scalpel near the crural nerves of a frog recently killed, lying not far from the conductor; the muscles of the limb were instantly set in motion, being agitated with strong convulsions. By a long series of new experiments, the law of nature, as far as respects the influence of this principle, was investigated, of which mere accident had at first afforded him a glimpse only. Galvani published a treatise on the subject, addressed to the Institute of Bologna, in the year 1791. On the appearance of this work, the universal attention of the philosophers of Europe was arrested. This discovery was made at a time when something more than hypothesis was necessary to satisfy the mind of the inquisitive inquirer after scientific truth. To this desire, may be referred the almost innumerable experiments which were made in every district in Europe, in consequence of this publication ; by which means the science became considerably enriched by the addition of a great variety of new facts, by contemporaries and successors, insomuch that it is said the labours of Galvani, the original discoverer, bear but a comparatively small proportion to what have been since adduced for its illustration.

Galvani found, that, by the mere agency of a metallic substance, where he had no reason to suspect the presence of electricity, the limbs of a recently-killed frog were convulsed ; and having ascertained the fact by a number of experiments, he in the course of his inquiries found that the convulsions or contractions were produced only when dissimilar metals were employed. It was now inferred that electricity is not only pro-duced by the friction of bodies, but even by the mere contact of certain substances. At the same time it was admitted, that these substances must have some chemical agency or action upon each other, and that the effect produced seems to be proportionate to the degree of chemical action. The following well-known facts were now supposed to be explained by this science. Porter taken from a pewter pot has always been held by connoisseurs in that liquor to be better than when taken from china or glass: this was now said to arise from a certain decomposition, effected by means of the liquor in the vessel - the porter and the saliva on the under lip coming in contact with the metal. Pure mercury retains its metallic splendour a long time, but its amalgam with tin, etc., is almost immediately oxydated or tarnished. Inscriptions of very ancient date, on pure lead, have been found in a perfect state, while others of modern times, made on compound metals, are corroded and scarcely legible. Works of metal, whose parts are soldered together by means of other metallic substances, soon tarnish, or are oxydated about the places in which the different metals are joined. So likewise is the copper on ships, which is fastened on by means of iron nails. Zinc also may be kept a long time under water, with scarcely any change; but if a piece of silver touch the zinc while under water, there will be very soon a sensible oxydation. Take a piece of zinc and place it under the tongue, and lay a piece of silver as big as half-a-crown on the tongue, and no particular taste will be observed ; but, bring the outer edges of the metals together and a very disagreeable taste will be per-ceived, which is said to arise from the de-composition of the saliva, a watery fluid. The same thing may be noticed with a guinea and a piece of charcoal. These fact's have been thus explained, and the theory generally admitted: - The conductors of electricity, however they may differ from each other in their conducting powers, may be divided into two classes. The first class, which are denominated the dry and more perfect conductors, consist of metallic substances and charcoal the second class, called also imperfect conductors, are waters, acids, etc. From these, or some of them, all Galvanic Circles, as they are named, are formed.

Hitherto this influence or agent had been chiefly investigated with reference to its operation on animal substances. Hence its popular name was for a long time, Animal Electricity : but it being soon found that its agency was more extensive, that it possessed powers not indicated by this denomination, and that of course the retention of this name would lead to error, the word Galvanism was adopted in its stead. This extension of the Galvanic principle was connected with new discoveries, and improvements from various quarters; these, however, for a considerable time, were generally small, and unimportant in their nature. But among all the recent discoveries in Galvanism, that made by Professor Volta, in 1800, is most remarkable in its nature, and most interesting in its relations. Volta 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, Vo/taism.