Abstract
Relative maximum velocities of incident and emergent photo-electrons from a thin Pt film.—Previous observers have obtained ratios of emergent to incident energies of 1.25 or more, contrary to the quantum theory, but these ratios are shown to be due to the rounding off of the feet of the current voltage curves as a result of the presence of stray light of shorter wave-length. When monochromatic light was used and precautions were taken to avoid stray light, a photo-electric cell of the ordinary type with a thin Pt film deposited on glass as target, gave straight line curves crossing the line of zero current at the same voltage point. Additional experiments showed that the maximum energy is the same in all directions and equal to 1.76 volt for 1850 A and.20 volt for 2540 A.