This article constitutes part of a dissertation submitted in July 1942 to the Faculty of the Graduate School of Yale University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. The writer is indebted to Dr. Walter F. Grether, Dr. Walter R. Miles, and Dr. Carl I. Hovland for their assistance in numerous technical matters, and to Dr. Donald G. Marquis for his critical reading of the manuscript. * For definitions of the technical terms used in this paper the reader is referred to Troland (»4). 24 * Technical considerations relating to the exit slit width and the purity of the entire spectrum for this slit width will be found in the original thesis (3). * This calibration was made by Dr. W. E. Forsythe of the General Electric Company. Actually the energy distribution contained a little too much green, but for purposes of the experiment, this deviation is probably not significant.