Extension of the field of use of the ballistic galvanometer

Abstract

The paper describes an extension of the field of use of the ballistic galvanometer as well as a novel method of measuring high resistance. Hitherto, tests performed with the aid of the ballistic galvanometer have been confined to the measurement of phenomena which impart to the galvanometer coil impulses lasting a short time compared with the galvanometer period, and to the measurement of small steady state currents. The use of the ballistic galvanometer is therefore somewhat restricted and, furthermore, galvanometers having a very long period are specially constructed. These long period galvanometers are very expensive, fragile and need a constant readjustment of the scale zero. They are generally cumbersome in use. The effect on the ballistic galvanometer of phenomena giving impulses which last for a time comparable with or even longer than the galvanometer period has been investigated in this paper. The effect of these latter impulses has been compared with corresponding short time effects, and the relation between the two has been examined. It appears that this relation is one of extreme simplicity and there seems to be no reason why ballistic galvanometers should not be used for measurements involving long period impulses. Tests have proved the theory and it seems that, as well as generally extending the field of use of the galvanometer, a new method of measuring high resistance has been found.