VOLTA

VOLTA, ALESSANDRO. See SIXTH DISSERTATION, § 740.

Voltaic Electricity. VOLTAIC ELECTRICITY properly designates that branch of electricity to which the name of Galvanism is generally applied. The term voltaic has been given to it in consequence of the science having been founded by M. Volta, professor of natural philosophy at Pavia, although the experiments of Galvani were prior to those of his countryman. At present we propose to comprehend under this general title, the sciences of galvanism, electro-magnetism, magneto-electricity, and thermo-electricity; and we have adopted this arrangement in order that we might avail ourselves of the various discoveries which might be made up to the close of the work.¹

Galvanism. The science of galvanism derives its name from some interesting experiments performed in 1789 by M. Galvani, A. D. 1789. professor of anatomy at Bologna. When one of his pupils was using an electrical machine, a number of frogs were lying skinned on an adjoining table for the purposes of cookery. The machine being in action, the young man happened to touch with a scalpel the nerve of the leg of one of the frogs, when, to his great surprise, the leg was thrown into violent convulsions. Madame Galvani, having observed the fact, communicated it to her husband, who speedily repeated and extended the experiment. He found that the convulsions took place when a spark was drawn from the prime conductor; and when the blade of the knife, or any other good conductor, was brought into contact with the nerve. When a frog formed part of an electric circuit, a very small quantity of electricity, whether common or atmospheric, produced convulsions in the muscles. Having hung a number of frogs by metallic hoops on an iron railing, he observed that the limbs were frequently convulsed when no electricity was indicated in the atmosphere. In studying this experiment, he was led to the conclusion that the convulsions were not produced by extraneous electricity, but that they always took place when the muscle and nerve of a frog were each placed in contact with metallic bodies, themselves connected by a metal. A still more powerful effect was produced when two metals, such as zinc and copper, were employed, the nerve being armed or coated with one of these metals, the muscle brought into contact with the other, and the two metals joined by an electrical conductor.

This experiment is shown in fig. 1, where Z is the rod