The Brownian movement of a galvanometer coil and the influence of the temperature of the outer circuit

Abstract

Some time ago, in connection with certain curves published from this Institute, and illustrative of the thermo-relay method for the magnification of galvanometer deflections, Ising pointed out* that the current irregularities superposed upon the baseline-current, as traced out photographically, could be interpreted as due to the Brownian movement of the suspended coil of the galvanometer, and indeed were of the order required theoretically. To prove definitely that these small variations are really due to the Brownian movements, it is evidently necessary to show that the temperature of the galvanometer system has an influence upon the mean value of the movement. The difficulties involved in maintaining the galvanometer itself at sufficiently low temperatures are great, and it is much more convenient to cool a series-connected coil in the outer circuit. This introduces the problem of the Brownian movement in a system at two different temperatures, and this has not, until recently, been investigated theoretically. The purpose of the present work is, then, to develop the necessary theoretical methods for such problems, and to obtain an expression for the Brownian movement which can be subjected to direct experimental verification.