Wheelock — Nature of Ionization Produced hy a Rays. 253 



% lack saturation 





at different 





5 



voltages 

 20 



100 



19-1 



10-9 



2-7 



9-2 



7-1 



0-4 



5-5 



3-4 



2-1* 



5-7 



2-3 



0-0 



Pressure Distance 



mm. from 



mercury chamber 



A 544-7 4-3 



B 354-0 4-3 



C 224-0 4-3 



D 224-0 9-0 



* The large value is probably due to an experimental error. 



4-3°"' at 544-7""" pressure corresponds to S'OS'"™ at 760""" pressure. 



4-3 " 354-0 " " " 2-0 " 760 



4-3 " 224-0 " " " 1-27 " 760 " 



9-0 " 224-0 " " " 2-65 " 760 " 



111 cases A, B, and C, the percentage lack of saturation 

 decreases as the pressure is diminished, which would be 

 expected on either hypothesis. 



In addition to the direct effect of diminishing the pressure 

 there is an indirect effect due to the change in range of the a 

 particle-prodiicing ions. Since the range varies inversely as 

 the pressure, diminishing the pressure and keeping the radio- 

 active source at a fixed distance (^-S*^"^) from the chamber is 

 equivalent to bringing the source nearer the chamber. This 

 indirect effect is small, however, compared with the effect of 

 decreasing the number of molecules of gas in the chamber. 



It is of interest to see how the curve represented by the 



equation, Qx = ^9 s log (l H — ^ ) , which was based upon 



the hypothesis of columnar ionization and a uniform distribu- 

 tion of ions within the columns, compares with the curves 

 experimentally obtained at reduced pressures. 



To make this comparison the values of gs were found, which 

 would make the equation fit the experimental curve (pressure 

 761""" mercury) at different potential gradients applied. 



2A;X 

 Values of as = — Tra'' were then calculated for pres- 



a 



sures of 354""° and 224™" of mercury respectively, taking into 

 account the variation of the mobility (Ic) of the ion, also the vari- 

 ation of a, the coefficient of recombination, with the pressure. 

 The mobility varies inversely as the pressure'* for the range of 

 pressure used. The variation of a with the pressure was obtained 



by plotting Langevin's values of e = — — , given by J. J, 



Thomsonf and interpolating for the pressures used. 



* Alois F. Kovarik, Physical Eeview, April, 1910. 



f Conduction of Electricity through Gases, by J. J. Thomson (second 

 edition), p. 73. 



