In order to explain the photographic effeets of pressure reported previously, a tentative theory of the latent image is presented. It is considered that the latent imnge consiste of deformed silver halide erystals of which the deformation must exceed a certain eritical value so as to render the crystals developable. The mechanism of ceformation due to the aetion of light is diseussed. The deformations in the erystal cansed by pressure when it is applied before or during exposure tend to aetivate the detaching of electrons from halide ions,a process which is essential in causing further deformation, However,the deformed regicns act at the same time as potential barriens so that the mobility of the detached eleetrons is loenlized. These two opposing tendeneies. the activation etfeet and the localization effeet,are in the opinion of the author responsible for the various phenomena observed.