190 BELL SYSTEM TECHNICAL JOURNAL 



the platinum. This electric intensity is found, using the optical 

 constants of platinum, by computing the intensities of the wave 

 patterns formed by the interference of the reflected and incident 

 beams. These computations are made for various angles of incidence 

 and for light polarized in and at right angles to the plane of incidence. 

 The intensities thus found exhibit very large ratios of value for the 

 two planes of polarization, in striking agreement with the character- 

 istics of the vectorial photoelectric effect. The changes of amplitude 

 of the perpendicular electric vector on entering the alkali metal film, 

 as computed from the optical constants of the alkali metal, account 

 for the experimentally found low values of the emission ratios at long, 

 and their high values, at short wave-lengths. 



The PhotoeJectric Effect from Thin Films of Alkali Metal on Silver}^ 

 Herbert E. Ives and H. B. Briggs. The thin films of alkali metals 

 which spontaneously deposit in vacuo on other metals have long been 

 known to exhibit photoelectric eiTects which vary in amount and 

 character, depending on the underlying material, but the exact nature 

 of this dependence has been obscure. Silver, because of its region of 

 exceedingly low reflecting power in the ultraviolet and the accom- 

 panying ^'ariation of optical constants, is exceptionally well suited 

 for studying the influence of the underlying metal. It is found that 

 the region of low reflecting power profoundly affects the photoemission, 

 but in a manner not to be explained simply by reduction of light 

 reflected back through the alkali metal film or by the absorption of 

 light by the silver. The results obtained are very satisfactorily 

 explained upon computing, from the optical constants, the intensity 

 at the surface, of the interference pattern formed by reflection just 

 above the silver surface. The positions of the maxima and minima 

 of photoemission, and their variations with angle of illumination and 

 plane of polarization are accurately indicated. 



The Applicability of Photoelectric Cells to Colorimetry}^ Herbert 

 E. Ives and E. F. Kingsbury. It is the purpose of this paper to 

 consider critically the requirements for a precision physical colorimeter, 

 and to estimate, in the light of a large body of experimental data on 

 the new types of photoelectric cells, to what degree the requirements 

 for physical colorimetry may be met at the present time. The paper 

 is intended to be very specifically limited to the problems of precision 

 color measurement, and it is assumed that the reader is already 

 acquainted with the principal facts relating to photoelectric cells and 



iop%5. Rev., October 15, 1931. 



" Jour. Optical Soc. America, September, 1931. 



