132 Photoelectric Properties of Thin Films of Platinum. 



(c) Possibly some part of the photoelectric effect is due to 

 some other radiation accompanying ultra-violet light, 

 which radiation is more easily absorbed by platinum 

 than light. Millikan's * work seems to show that 

 this is not very probable. 



Prof. C. H. Lees suggested another possibility to me, that 

 the form of the light-waves may have an influence on the 

 dissymmetry. It is supposed that light-waves are modi- 

 fied in going through matter. Some experiments were 

 performed by Stuhlmann f which seem to support this view. 

 He showed that the dissymmetry was much less marked 

 when the light had to pass through a greater thickness o£ 

 quartz, and explained this by the absorption of light by 

 quartz. As quartz does not absorb ultra-violet light appre- 

 ciably, it seems probable that the view here suggested might 

 have some bearing on the dissymmetry. 



14. Summary of Results, 



1. y currents and y velocities are both unity for the 



same thickness of film. 



2. The dissymmetry for velocities is not so strongly 

 marked as for currents. 



3. As the thickness of film increases through 10~ 7 cm., 

 the photo-current increases suddenly. 



E 



4. The ratio j- currents is constant for films thinner than 



10 ~ 7 cm. and begins to diminish after the sudden increase in 

 current has set in. 



5. Radiations from the spark produce much quicker 

 electrons than those from the arc. 



6. The dissymmetry is more strongly marked the quicker 

 the electrons produced. 



7. It has been shown that it is possible that photoelectrons 

 possess sufficient energy to ionize molecules of platinum, and 

 that it is this which leads to the best explanation of the 

 sudden rise of photo-current at 10 ~ 7 cm. 



8. The thickness of film which gives the sudden rise in 

 current is the same for slow and quick moving electrons. 



9. The orientation of the plane of polarization of the light 

 has no influence on the dissymmetry. 



East London College, 

 Oct. 24th, 1912. 



* Loo. cit. f Loc. cit. 



