﻿On Photo-Fleet vie Fatigue. 



Zoo 



The following table gives the viscosities deduced from a 

 comparison of transpiration times : the same conditions do 

 not hold throughout, but only for each comparison. 



Gas. 



Mean Eatio of Transpiration 

 time to that of Air. 



Mean Temp. 



fi. 



i Air 



Direct calculation. 

 48-5 

 101 -o 

 60-8 

 75-5 

 560 

 75 7 5 



ll°-75 C. 

 12°-25 C. 

 12°-60 C. 

 12° -90 C. 



•000180 

 •0000864 

 •000145 

 •000133 



i Hydrogen 



i Carbon dioxide... 



i 



1 



I take the opportunity of thanking Professor Wilberforce 

 for constant interest and advice, in this and in other work. 



Georpre Holt Physics Laboratory, 

 University of Liverpool. 



XXIT. Photo-Electric Fatigue. By J. Robinson, M.Sc, 

 Ph.D., Demonstrator in Physics at the University of Sheffield*. 



SOME very interesting results on photo-electric fatigue 

 were given by H. Stanley Allen in the Phil. Mag. for 

 October 1910. He showed that the fatigue takes place 

 practically at the same rate in darkness as in light, that it is 

 independent of the electric field, but that the size of the 

 vessel used has an influence on it. Some results which are 

 brought forward in the following seem at first sight contra- 

 dictory to those of Allen. To understand these differences, 

 it will be necessary to consider closely the conditions under 

 which the different experiments were made. 



Allen polished his plates immediately before an experiment, 

 and measured the photo-electric currents at atmospheric pres- 

 sure directly afterwards, making measurements at regular 

 intervals. He found the current to diminish with the time, 

 and the rate of diminution to be independent of light. 



In the present experiments, the electrodes were polished by 

 rubbing with steel, and inserted in a glass vessel which was 

 pumped out to a high vacuum as quickly as possible. The 

 experiments were made under these conditions, and extended 



Communicated bv the Author, 



