The Primary Process in the Formation of the Latent Photographic Image

I HAVE read with much interest the communication from Dr. F. C. Toy and Mr. G. B. Harrison in NATURE of May 4, 1929, p. 679. The experiments described on the photo-conductance phenomenon in silver bromide afford valuable confirmation of the results obtained by Dr. W. Vanselow and myself on the photo-voltaic effect at silver bromide: silver electrodes, which were briefly described in the sixth Hurter and Driffield Memorial Lecture.1 These results, we consider, not only demonstrated the primary separation of electrons by light in the photolysis of silver bromide, but also gave the first evidence that this separation of electrons is actually related to the liberation of bromine. The negative potential difference ascribed to electron liberation is produced within 1600 second of the incidence of the light, attaining a maximum within 165 to 120 second.