I. INTRODUCTION To create an electrostatic latent image, a photoreceptor is uniformly charged by a corona discharge, then exposed to an imagewise pattern of radiation that selec­ tively dissipates the surface potential in the exposed regions. To be useful for creating visible images, it is necessary that the surface potentials be sufficiently high for image development and persist in the dark for periods of time well in excess of the time between the exposure and the image development steps. In practice, the surface charge is determined by the current output of the corona charger, the time of exposure in the corona discharge, the charge acceptance, and the rate of dark discharge of photoreceptor. Thus the charge acceptance and rate of dark discharge are of considerable importance to xerography.