Stabilization of Disturbing Magnetic Field upon the Interior of an Artificial Field Coil for Testing Compasses

When doing experiments about magnetic elements such as parts of magnetic compasses, a weak magnetic test field is often required. Especially, if there is heavy traffic near the test place, the magnetic field varies depending not only on the fluctuation of geomagnetic field, but the heavy magnetic influence caused by the traffic. In the urban area much magnetic effects are superposed. These magnetic disturbances greatly affect upon the weak test field direction. The Authors measured such disturbing magnetic fields, such as the ones caused by the traffic, and tried to cancell them, by using a controll circuit and a Helmholz coil. The result showed that even the fluctuation of geomagnetic field as well as the effect of magnetic disturbances produced by external causes were cancelled to the level of one tenth of the diurnal variation of the geomagnetic field.