334 Mr. Otto Stuhlmann on a Difference in Photoelectric 



produce. Different observers have shown that beams of 

 similar composition under similar conditions produce a photo- 

 electric effect proportional to the intensity of the light, unless 

 the intensity is very small. 



If there were no difference in the photoelectric effect pro- 

 duced by incident and emergent beams of the same intensity, 

 the value of the ratio A/B for Position (1) should always be 

 less than that of A/B in Position (2), on account of the 

 absorption by the quartz plate and by the film. As a matter 

 of fact the reverse was always found to be the case with thin 

 films, showing that the ionization is greater for an emergent 

 than an incident beam of the same intensity. It is not 

 difficult to allow for the absorption by the quartz plate, as 

 will be shown below, but the absorption by the film is a more 

 serious matter. This arises from the fact that these films 

 are so tbin that the electrons must be regarded as produced 

 throughout the volume of the film. The method was there- 

 fore adopted of seeing if the value of the ratio of the fractions 

 A/B in the two positions did not approach a limiting value, 

 as the thickness of* both films was indefinitely diminished. 

 This was found to be the case, as will be seen in the sequel. 

 Under these circumstances one could be certain that the 

 limiting value corresponded to the case in which the absorp- 

 tion of the light by the film was negligible ; so that, after 

 allowing for the absorption by the quartz plate, the only 

 difference between the ratio A/B in the two positions in the 

 limiting case will arise from a difference in the ionization 

 produced by incident and emergent beams of equal intensity. 



The following table gives a set of readings characteristic 



Platinum Set 20. 



Position (1). 



Position (2). 



B-A. 



B. 



A. 



A/B. 



B-A. 



B. 



A. 



A/B. 



20-0 



76-0 



56-0 



•736 











27-0 



99-3 



723 



•726 



39-0 



1150 



76-0 



•661 



25-0 



95-0 



70-0 



•737 



25-0 



70-5 



45-5 



•647 



31-0 



1150 



84-0 



•731 



310 



88-5 



57-5 



•649 



35-0 



140-0 



105-0 



•750 



35-2 



102-8 



67-6 



■657 



27-0 



990 



720 



•729 



26-0 



74-0 



48-0 



•649 



42-0 



178-0 



136-0 



•763 



42-0 



118-0 



76-0 



•644 



30-0 



117-5 



87-5 



•744 



380 



108-0 



700 



•649 







Avera^ 



je -739 

 Ratio T^y 



= 113 





Avera^ 



;e -651 



