A galvanometer is an electromechanical instrument for detecting and measuring electric current. The most common use of galvanometers was as analog measuring instruments, called ammeters, used to measure the direct current (flow of electric charge) through an electric circuit. A galvanometer works as an actuator, by producing a rotary deflection (of a "pointer"), in response to electric current flowing through a coil in a constant magnetic field.
Galvanometers developed from the observation that the needle of a magnetic compass is deflected near a wire that has electric current flowing through it, first described by Hans Oersted in 1820. They were the first instruments used to detect and measure small amounts of electric currents. The name comes from the Italian electricity researcher Luigi Galvani, who in 1791 discovered the principle of the frog galvanoscope – that electric current would make the legs of a dead frog jerk. Wikipedia, Galvanometer