Abstract
In principle, the nuclear magnetometer is sensitive only to the total intensity of the geomagnetic field. However, it becomes also possible to measure the component or the direction of the field by adding adequate artificial field. This paper reports the general principle of measuring H, Z and D with proton precession magnetometers. Effects of erroneous set-tings of a theodolite and the coil which generates artificial uniform field are eliminated by the suitable combination of observational positions of the instrument. Several types of instruments which have been and now being developed in Geographical Survey Institute are also introduced.
