Galvanometer Amplification by Photo-Cell

Abstract

IN 19311¹ described the use of a differential photoelectric cell connected to a ‘secondary’ galvanometer for amplifying the movements of a ‘primary’ one. The only suitable cell available then was a cuprous oxide one, and the current produced by it was not great enough to allow a quick (and therefore insensitive) secondary galvanometer to be used; consequently, although sufficient amplification was obtained, the movements were slowed. This slowing of movements is an even greater objection to the thermal relay of Moll and Burger since the thermocouple introduces a further lag which the photo-cell does not.