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. The simplest form a j of galvanometer is a magnetic needle a 8 poised upon a point, and surrounded by M ■ one or more coils of copper wire covered 1 "t* ) with silk, the ends a and b being either I left free, or terminating in two small copper cups containing mercury, for the concvenience of communication with the source of electricity. When this needle is placed paiallel to the coil, and in the magnetk 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 cast or the west, according to the direction of the current. Sec ElectboMaqnk i [s. 501]