In most phototubes

the photosensitive material of the cathode is deposited on the isolating wall

and the phototube is often made of the central-anode type.This form

with a small central anode surrounded by a large semispherical or round cathode

finds various applications.As the methods of using the phototube are different

so will be the potential distribution in the phototube. In this paper

the potential distribution and its influence on the properties of the phototube are discussed under two conditions:with parallel light falling uniformly on the emissive surface

secondly

with converging light focussing on the center point of the cathode. In the latter case

potentials between points along the axis of the cathode and the anode are calculated.Significance of such potentials are also given.