The Latent Photographic Image

Abstract

IN a recent letter to NATURE (Nov. 15, 1930) A. P. H. Trivelli replies to our criticism (Proc. Roy. Soc., A. 127, 613; 1930) of his “elementary voltaic cell” theory of latent image formation, originally put forward by him in 1927 (J. Franklin Inst., vol. 204, 649), and concludes that our criticism is not justified. It seems from his letter that he has not realised the significance of our experimental results as they affect his theory. We agree with him, of course, that the larger the silver nucleus originally present in the grain, the less is the amount of silver which must be added during the exposure in order that a development centre may be produced, and hence the greater the sensitivity of the grain. But quite independently of the absolute mass of silver which (according to Trivelli's theory) must be deposited electrolytically during the exposure, his theory demands that the electrolytic current in the light shall be enormously great relative to its value in the dark. We say this is extremely improbable, mainly because our experiments show that illumination causes little, if any, increase in the electrolytic conductivity of silver bromide.