W. Ujanin² has used the earth inductor for the measurement of intensity. He does not, however, discuss the feasibility of his various schemes for observations on a vessel or in an airship. Of the two marine methods for determining intensity used by the Department of Terrestrial Magnetism, viz., the Dip Circle and the “Sea Deflector,”³ the second is undoubtedly the better. The instrument is essentially a sine magnetometer, the suspended magnet being a compass card (liquid).