﻿7l ; G Profs. Welliseh and Bronson on the Distribution of 

 Emanation in Air at 250 mm. pressure. 



Potential in 

 volts. 



Percentage cathode 

 activity. 



6* «o i— 



81-2 

 8P9 

 82-1 



6. Experiments with Air at Pressures greater than 

 1 atmosphere. 

 Several experiments were performed to ascertain the dis- 

 tribution ot activity when the air in the testing vessel was at 

 a pressure greater than 1 atmosphere. The results are given 

 in Table TIL; they were obtained in the early stages of' the 

 research when little information was at hand concerning the 

 distribution of the activity for various potentials. For this 

 reason the experiments appear very unsystematic ; however, 

 the results will serve to convey a good idea of the difficulty 

 of obtaining approximate saturation of the activity, even 

 with large applied potentials. 



Table TIL 



Pressure, 



Potential in 



Percentage cathode 



atm. 



volts. 



activity. 



1-6 



+ 700 



G8-8 



2-0 



6o0 



64-1 



25 



160 



552 



25 



750 



60- J 



3 13 



880 



57*5 



3 3:$ 



3750 



80-6 



353 



750 



53-8 



The difficulty of saturating the ionization current through 

 the gas likewise made itself manifest at these pressures ; as an 

 example it may be mentioned that with an applied potential 

 of 1100 volts the ionization current due to a constant source 

 of radiation increased as the pressure was increased from 1 

 to 2\ atmospheres, and then continually decreased with any 

 further increase in the pressure. 



These considerations afford an explanation for the maximum 

 of cathode activity which has been found by several experi- 

 menters to set in at certain pressures when a constant potential 

 is employed. 



