﻿by Moving Electrified Particles. 453 



Ionization by Positively Charged Particles. 



In this case, as the mass of the moving particle is very 

 large compared with that of the corpuscle, M 2 is large com- 

 pared with M 2 , so that the equations 



r, 4M X M 2 m . 9 ^ . 9A 1 



Q = /Tt/r \A* T sin o> sm e = 





reduce to 



QiJ-lVlo -9/1 • 9- /I J" 



= -ir sin ^' Bmga : wv* ; 



or if T' is the kinetic energy of a corpuscle moving with the 

 velocity of the positive particle^ 



Q=4T'sin*0; sin a = 



or -_/*?! 



"I Q 



1 + 



//IT' \ 



d 2 



4T x 2 i 2 



r j,, 2 c jl^ . 



Thus the number of ions made per centimetre of path by 

 the action of the positively charged particles on the negative 

 corpuscles is, when T' is large compared with W, 



mre 2 W 

 WT' • 



Thus when £ = E the number of ions produced by the 

 positively electrified particle is the same as the number pro- 

 duced by a corpuscle moving with the same velocity. When, 

 as in the case of the u particles,- E — 2<?, the ionization 

 produced by the a. particle is four times that produced by a 

 corpuscle moving with the same velocity. We can test this 

 result by comparing the ionization due to the a particles 

 from radium C, which have an initial velocity of 2*06 x 10 9 

 cm./sec, with that due to Glasson's cathode rays with the 

 velocity of 4*7 X 10 9 cm./sec. In consequence of the slower 

 velocity the a particles ought by our rule to make (4'7/2'OG) 2 

 or 5"4 times the number made by the cathode particles, and 

 in consequence of the double charge 4 times the number; 

 hence the a particle should make 4 x 5*4 or 21 times as many 

 as the cathode ray. As the cathode ray makes 1140 the 

 a particle should make 23940 ions per centimetre ; the number 

 as measured by Geiger is 22500, the difference is not greater 

 than could be accounted for by errors in the experiments. 



