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Abstract
A general account is given of a new and comprehensive theory of the nature and formation of the photographic latent image. The difficulties which are experienced in the application of the Gumey-Mott theory to a number of aspects of latent image formation and photolysis are first outlined and it is pointed out that they arise principally from the fact that recombination between electrons and positive holes was not considered by these authors. The new theory is then presented together with such experimental evidence as is available to support the successive stages which are postulated. Attention is drawn to the possible role of crystal imperfections in photographic sensitivity and a new approach to the treatment of dye sensitization is suggested which removes a number of outstanding theoretical difficulties. The account is fully illustrated with photomicrographs, diagrams and energy level diagrams which have not been included in previous general papers. Four basic principles which may serve to focus attention on important features of the mechanisms of photochemical change in silver halide crystals are formulated in the concluding section.