A sine galvanometer for determining in absolute measure the horizontal intensity of the Earth's magnetic field

A brief historical statement was made with reference to the measurement of the horizontal intensity of the earth's magnetic field by electrical methods, and a general description of sine and tangent galvanometers was given, with the suggestion of an improvement in the latter. Then followed a detailed description of a new sine galvanometer, constructed, with certain exceptions mentioned below, in the workshop of the Department of Terrestrial Magnetism. The base of the instrument, including the tripod, circles, etc, was taken from one of Wild's theodolites, constructed by Edelmann, and was much improved by the substitution of non‐magnetic parts for parts too magnetic, and by the substitution of electrical illumination of the precision circle for daylight illumination by mirrors.