Ionization hy Charged Particles. 



805 



with a velocity greater than V 2 when the velocity of the 

 primary is V x ; the figures are the means of those obtained 

 by Gehrts with several different metals. The column 

 V 1 = c© gives the corresponding figures obtained in the 

 experiments (10) for 8 rays liberated by /3 rays under 

 conditions which seem to make them comparable with those 

 of Gehrts. 



Table I. 



v\ = 



80 



260 



500 



00 



V.,-0 



1-000 

 0-506 

 0-267 

 0-167 

 0113 

 083 

 0-064 

 0-046 

 0-038 

 0023 



1-000 

 0-445 

 0-220 

 0-129 

 0-084 

 0-060 

 0043 

 0032 

 0026 

 0-014 



1-000 

 0-433 

 0-208 

 0-120 

 0-079 

 0-053 

 0036 

 0027 

 0021 

 0-008 



I '000 



0-400 

 0-198 

 0-112 

 0064 



0-004 



2 



4 



' 6 



8 



10 



12 ... 



14 



16 



20 





When the speed of the primary rays lies between 11 and 

 80 volts, the 8 rays are mixed with reflected rays and no 

 precise measurements of their velocities have been obtained. 

 In the reflected rays the proportion of electrons having a 

 given velocity increases as that velocity approaches that of 

 the primary rays, while in the 8 rays it increases as that 

 velocity approaches zero. 



5. Some further experiments have been made on the 

 8 rays liberated by slow ft rays in the hope of throwing 

 fresh light on the mechanism of ionization. Most of these 

 were made with an apparatus essentially similar to that 

 employed by Gehrts (5) ; the results of them need not be 

 described in detail, because they resemble so closely those 

 obtained by Gehrts. Attention was especially directed to 

 three questions : — 



(1) Is it certain that no true 8 rays are liberated by 

 primary rays of a velocity less than 11 volts ? 



.Evidence for the existence of ionization, as distinct from 

 reflexion, would be obtained if the number of electrons 

 leaving the plate were greater than the number of the 

 primary rays falling on it. The velocity of the primary 

 rays for which these numbers are equal gives a maximum 

 estimate of the least velocity required for ionization. The 



Phil. Mag. S. 6. Vol. 25. No. 150. June 1913. 3 I 



