The Tamm Level and Reciprocity Failure

Abstract

Early grain counts imply that the entry of two photo-electrons into a unique feature of the grain makes certain the formation of a development centre either internal or external, the site being decided afterwards. The unique feature is identified with the Tamm conducting surface level, lying between the crystal and a colloidal coating formed during digestion. The Tamm level separates order from disorder and is undisturbed by the external centre but is obstructed by the internal which interferes with the ordered crystal surface. The commercial emulsion favours the external image, the undigested emulsion the internal. Both are affected by recombination of the first electron, and the properties of the colloidal coating, which alone is sensitive to weak light, are deduced. The external centre is a new source of low intensity reciprocity failure for the internal image, and the internal centre a new source of high intensity reciprocity failure for the external image. The early grain counts are identified with those for an undigested emulsion developed “to completion”.