(a) A reflecting galvanometer, with heavy magnetic needle, dampened by a
copper frame. It was devised by Weber.

(b) An apparatus for measuring the intensity of magnetic force. It may
consist of a magnet suspended by bifilar or by torsion suspension. A
reflecting mirror and scale as in the reflecting galvanometer may be
used to act as indicator of its motions. It is used in investigations of
the intensity of the earth’s field.

If the motions of the spot of light are received on a moving strip of
sensitized paper and are thereby reproduced photographically, the
instrument is self-recording. Such an apparatus is used in the Kew
Observatory, Eng., for recording the terrestrial magnetic elements.