A type of galvanometer, now rarely used, in which a small magnetic needle is pivoted horizontally at the centre of a vertical coil that is adjusted to be parallel to the horizontal component of the earth’s magnetic field. When a current I is passed through the coil, the needle is deflected so that it makes an angle θ‎ with its equilibrium position parallel to the earth’s field. The value of I is given by I=(2Hrtanθ‎)/n, where H is the strength of the earth’s horizontal component of magnetizing force, r is the radius of the coil, and n is the number of turns in the coil. Although not now used for measuring current, the instrument provides a means of measuring the earth’s magnetizing force.