On the Asymmetric emission of Photo-Electrons from Thin Films of Platinum. I

A S early as 1889, W. Hallwachs 1 showed that a photo-electric effect could be obtained from a silvered quartz plate when light was incident through the quartz.Later Rubens and E. Ladenburg 2 took up the work and observed a similar effect for gold leaf.They found the ratio of the photo-electric effect for incident and emergent light to be 100 to unity while the fraction of the ultra-violet light transmitted, photo-electrically measured, was one one-thousandth of the incident.The work was taken up by the writer 3 who showed that the photoelectric effect of thin cathode films of different metals deposited on quartz depends on the thickness of the film and whether the film is on the side of the quartz facing the light (incident effect = /) or on the side away from the light (emergent effect = E).The ionization currents were measured in air.It was shown that when the films are thin enough, about io~7 cm. or less, that the ratio emergent to incident currents (E/JT) was greater than unity and for thicker films less than unity.This ratio was constant for thin films and was shown to be equal to 1.17 for platinum.Independent experiments carried out by R. D. Kleeman 4 both in hydrogen and in vacuo led to the same conclusion as to the asymmetry of the photo-electric effect for emergent and incident light.Recently J. Robinson 5 showed that the above observed dissymmetry of emission should be separated into two quite distinct effects; the actual number of electrons emitted and the velocities of the electrons emitted.As TO THE ACTUAL NUMBER OF THE ELECTRONS EMITTED.It was shown by Robinson 6 that the magnitude of the ratio of emergent to incident current depended upon the source of illumination.When the