Time Lag in the Formation of the Latent (Photographic) Image

Abstract

Two distinctly separate series of constant energy exposures were made on Hammer Extra-Fast Plates at several different light intensities. Another short series was made on a Hammer Slow Emulsion. The intermittent but constant energy exposures were provided by two different rotating mirrors whose ranges of speeds were 1900 r.p.s. and 750 r.p.s., respectively. The emulsion grains were illuminated for periods varying from 10-5 second to 5.5×10-8 second duration. The rotating mirrors made it possible to obtain data on the intermittency effect for much shorter time exposures than was possible for Davis or for Weinland using selected wave-lengths. In this study, the apparatus permitted, by the use of unselected wave-lengths from light sources, the consideration of the intermittency effect with reference to the influence of intensity upon the exposed emulsion at a constant ratio of rest to flash period, and as well for small changes in this same ratio. The data secured have a bearing on the Brush effect. The diffuse densities of the images on the emulsions were measured by an adaptation of the Richtmyer differential photoelectric photometer. With a decrease in the time of duration of the flash, there was found a gradual diminution of the image density until a critical flash interval or period was reached, after which the density-flash period curve fell rapidly with small decreases in the flash period. The breaking point in the curve varied within experimental limits for the two mirrors but for high light intensities approximated 1×10-7 second while for the lower intensities the break occurred in the region of longer intervals. The conclusions reached from the interpretation of the data are: that the quantum theory applied to light in this particular field fails; that the real intermittency failures of any magnitude occur in the region of shorter flash or exposure intervals; and that the formation of the latent image can probably be explained as a resonance process.