Velocity oj Electrons expelled by X-rays. 753 



gas was thus enormously reduced and that due to the elec- 

 trons from the copper became the principal part of the total 

 ionization ; in addition, the range of pressure over which 

 the ionization-pressure curve was obtained was greatly 

 increased, and the sensitiveness was consequently increased. 

 These changes and the substitution of Wilson's Tilted Elec- 

 troscope for that of ordinary pattern were necessary on 

 account of the smallness of the total effect of the corpuscular 

 radiation emerging from the surface of a plate exposed to 

 copper K-radiation. 



In this case after applying the calculated factor, a com- 

 parison of the curves showed them to be identical. There 

 is thus no observable difference between the velocities of 

 K and L electrons emitted by copper under exposure to a 

 particular X-radiation. The maximum velocity and distri- 

 bution appear identical. 



The general conclusion is that though the K and L 

 corpuscular (electronic) radiations have many distinctive 

 properties, or more correctly have distinctive associations, 

 after emission from the parent substance they do not possess 

 distinctive velocities, or the velocity differences are very 

 small if not inappreciable. 



Summary. 



If the electrons in the corpuscular radiation from sub- 

 stances exposed to X-radiation were ejected under the same 

 conditions as those ejected by ultra-violet light, the experi- 

 ments of A. L. Hughes would lead us to expect well marked 

 differences in the velocities from various substances. Careful 

 experiments have shown these differences do not exist. 

 The maximum velocity of ejection does not depend upon the 

 particular substance from which the electron is ejected. 

 (Possible error 1 to 2 per cent.) 



The Kand L electrons ejected from a particular substance 

 under the action of X-rays, though those electrons are 

 different in origin and in association, are emitted with 

 approximately the same velocity. (In one case a variation 

 which might be interpreted as a difference of about 8 per cent, 

 was observed, though in another there was no suggestion of 

 any difference outside the possible error of 3 or 4 per cent.) 



[We should like to express our indebtedness to Mr. J. E. H. 

 Hagger for his valuable help in these experiments.] 



