The Summation of Different Color Radiations by a Photographic Emulsion*†

The problem of determining the manner in which a photographic emulsion sums different color radiations divides itself naturally into two parts depending upon whether the different radiations are applied simultaneously or successively. The first part of this problem was thoroughly investigated by A. Van Kreveld who announced a beautifully simple theoretical law for the manner in which an emulsion adds different colors applied simultaneously. In the first part of the present paper results are presented in verification of Van Kreveld’s summation law. The second, and main, part of this paper is concerned with the addition of colors applied successively. A special technique had to be developed for the execution of these experiments and for the reduction of the data. The method of making the exposures consisted of crossing intensity scale curves, and the comparison of the separate and combination color exposures was carried out by graphical means. The results show that an emulsion adds radiations of different color (applied simultaneously or successively) according to the same rule that it adds radiations of identical quality. Van Kreveld’s summation law was tested for the case of successive addition and was shown to hold in a restricted form here also. A brief discussion of the theoretical significance of the results is included.