﻿722 Profs. Wellisch and Bronson on the Distribution oj 



The similarity was so striking as to suggest a more detailed 

 study of the ionization curves for emanation in equilibrium 

 and with different applied potentials. 



It was found that within the limits of error the ratio of the 

 two ionization currents obtained for two potentials not too 

 low* was, like the percentage cathode activity, independent 

 of the amount of emanation in the vessel ; and, moreover, 

 that this ratio was identical with the ratio of the percentage 

 cathode activities corresponding to these two potentials. 



As an example of the results obtained in this connexion it 

 will suffice to compare the ratio 1*09 of the percentage 

 cathode activities obtained with potentials 975 and 160 volts 

 respectively with the corresponding ionization currents. 

 From our values for the ionization currents in air at 1 

 atmosphere pressure obtained in three experiments when 

 widely different quantities of emanation were employed, we 

 deduce the following figures: — 



Ratio of current with V volts to that with 1G0 volts : 

 = 1-10 when V = 875. 

 = 1-10 when V = 980, 

 = 107 when V=900. 



It would serve no useful purpose to reproduce in full any 

 oE the ionization curves because, in the first instance, the 

 early slope of the curve depends markedly on the amount of 

 emanation employed, and, secondly, because the comparison 

 could only be made over the limited range from about 100 

 to 1000 volts, as the ionization current could not be accurately 

 measured when the larger potentials were employed. 



That the equality of the ionization and activity ratios still 

 holds approximately at low voltages when a constant amount 

 of emanation was employed was verified by measuring the 

 percentage cathode activity with 18 volts applied, and the 

 ionization currents for 18 volts and higher potentials, it 

 being known that the percentage cathode activity at the 

 higher potentials was independent of the amount of emanation 

 : in the vessel. The following results were obtained : — 



Percentage cathode activity with 18 volts: 42'7. 



Ditto 1G0 volts: 79T. 

 Ratio : '54. 



Ionization current with 18 volts : 6 # G. 



Ditto 160 volts: 11-4. 

 Ratio : *58. 



* The potentials should be sufficiently large to prevent volume re- 

 combination as distinguished from columnar recombination, i. e. should 

 be sufficient to saturate a uniform distribution of Rontgen ray ions equal 

 in number to those produced by the a radiatim. 



