An instrument for detecting and measuring small electric currents, invented by Luigi Galvani. In the moving-coil instrument a pivoted coil of fine insulated copper wire surrounds a fixed soft-iron core between the poles of a permanent magnet. The interaction between the field of the permanent magnet and the sides of the coil, produced when a current flows through it, causes a torque on the coil. The moving coil carries either a pointer or a mirror that deflects a light beam when it moves; the extent of the deflection is a measure of the strength of the current. The galvanometer can be converted into an ammeter or a voltmeter. Digital electronic instruments are increasingly replacing the moving-coil type. See also ballistic galvanometer.