494 Wellisch and JBronson — Distribution of the Active 



The increase of the percentage cathode activity in the neigh- 

 borhood of 2000 volts is probably real, although the number 

 of experiments in this connection is not yet sufficient to justify 

 any definite statement. It is, however, of interest to record 

 that throughout the exposure with these high potentials a 

 large current due to ionization by collision was passing through 

 the gas. 



Finally, it might here be mentioned that a complete set of 

 observations for the distribution of the activity with various 

 applied potentials, both for air at 1 atmosphere and for air at 

 a pressure of 250 mm , had previously been made, using the same 

 test-vessel, but with the guard-tube projecting a short distance 

 into the volume of the gas. By reason of this some of the 

 activity which belonged properly to the cathode was measured 

 as " case activity," so that the resulting values for the percent- 

 age cathode activity were too small. The curves obtained both 

 for activity and ionization exhibited the same general features 

 as those previously described. Some of the results obtained 

 are given below ; these figures are not comparable with those 

 given above, which were all obtained after the guard-tube had 

 been cut down. 



Emanation in Air at 1 atmosphere. 



Potential in 

 volts 



Percentage cathode 

 activity 



160 



880 

 2750 



76-2 

 84-1 

 86-2 



Emanation in Air 



at 250 mm pressure. 



Potential in 



volts 



Percentage cathode 

 activity 



160 



920 



2500 



81-2 

 81-9 



82-1 



6. Experiments with Air at Pressures greater than 

 1 atmosphere. 



Several experiments were performed to ascertain the distri- 

 bution of activity when the air in the testing vessel was at a 

 pressure greater than 1 atmosphere. The results are given in 



