122 



Dr. J. Robinson on the Photoelectric 



at which the sudden increase in current takes place was 

 found to be 10 ~ 7 cm. 



Fijr. 4. 



400 



300 



200 



I 



100 





















































ki 





















1 



kj 



y_ 



Ik. 























N 













i 

















/ 





















1 

































40 80 120 



TH/CKfi/£SS of F/lm. 



160 



200 



Seconds^ 



Another point of interest is the decrease in the magnitude 

 of the currents for films thicker than 10~ 7 cm. It was at 

 first thought that this diminution was spurious, and that it 

 was due to the films beginning to absorb any traces of gas 

 left in the apparatus. The consistency with which this 

 effect was obtained in later experiments leads to the belief 

 that it is not spurious, and that ifc is in some way connected 

 with the sudden rise in current preceding it. 



Still another point of interest is the fact that for films 



thinner than 10 ~ 7 cm. the ratio y currents is practically 



constant, and that it only begins to diminish when the sudden 

 rise in the actual magnitude of the currents takes place. 



7. Maximum Values of the Ratio 



E 



E 



The constant value of the ratio y currents for films 



thinner than the critical thickness 10 " 7 cm. was well marked 

 in all the experiments performed. This ratio was found here 

 to be at least 1*22, whilst Stuhlmann did not obtain experi- 

 mental values greater than 1*14. This difference is so con- 

 siderable that it was necessary to inquire whether there was 

 some flaw in my apparatus. One of the films which gave a 

 ratio 1*26 was taken, and the conditions of the experiment 



