GALVANISM

(From Galvani, profe or of anatomy at Bologna, the discoverer of some of the phenomena connected with this form of electricity in the year 1790.) Under this term are frequently included the phenomena of Voltaic electricity (which see). We shall here limit it to the apparent evolution of electricity by the contact of different metals: this is best observed by the muscular contractions which are produced in the leg of a frog recently killed, when two different metals, such as zinc and silver, tin and gold, ., one of which touches the crural nerve, and the other the muscles, are brought into contact. Every time the metals touch each other the limb becomes powerfully convulsed; and if the experiment be made with a dead rabbit, so that one of the metals be in contact with the brain, and the other wiih the muscles of the extremities, the whole body of the animal is strangely agitated. Similar experiments have been made upon the bodies of criminals shortly after execution. These results, which have till lately been considered to depend upon the effects of electricity excited by the contact of the metals upon the nervous and muscular systems, led Volta to his celebrated researches, which terminated in the discovery of the Voltaic battery. Nearly all the cases, however, of the apparent production of electricity by contact have been satisfactorily traced by Faraday to chemical action. See Voltaic Battery. GALVANOMETER, An instrument for ascertaining the presence of a current of electricity, especially Galvanic or Voltaic electricity, by the deviation which it occasions in the magnetic needle. J The simplest form of galvanometer is a magnetic needle poised upon a )- point, and surrounded by one or more coils of copper wire covered with silk, the ends a and h being either left free, or terminating in two small copper cups containing mercury, for the convenience of communication with the source of electricity. When this needle is placed parallel to the coil, and in the magnetic meridian (as represented in the margin), it immediately deviates when the electric current pa es through the coil; and the deviation is either to the east or the west, according to the direction of the current. See ElectroJVIagnetism. [s. 497]