﻿452 Sir J. J. Thomson on Ionization 



the velocity of Eve's rays will be V 1140/48, or 4' 7 times 

 those of: Glasson's. As the latter rays had a velocity of 

 4-7 xlO 9 , the velocity of Eve's rays would be 2'2 X 10 10 , 

 which is a very reasonable value for the velocity of the ft rays. 

 We have neglected the correction for the alteration of the 

 mass of the ft rays with their velocity ; this correction would 

 have the effect of reducing slightly the calculated velocity of 



the ft rays. As the ionization in a gas is equal to T^m, and 



as n is proportional to the atomic weight of the gas, the 

 number of ions produced by a cathode ray of given velocity 

 moving through given gases will be proportional to the density 

 of the gas divided by W, the energy required to ionize an 

 atom of the gas. Hence W will vary as the density of the gas 

 divided by the ionization per cm. of path. Kleeman (Proc. 

 Royal Soc. Ixxix. p. 220) gives the relative ionization in 

 different gases produced by ft rays. From his values I have 

 calculated the relative values of Q for several gases : — 



Gas.. 



H. 



C. 



N. 



0. 



S. 



CI. 



Br. 



I. 



W... 



1, 



4-75, 



5-26, 



4 9, 



3-6, 



4-5, 



5-4, 



5-6. 



Thus it would appear from this result that hydrogen is 

 much more easily ionized than any of the other substances 

 tried. 



The deflexion which we have been considering of a rapidly 

 moving corpuscle by another corpuscle would not give rise 

 to much dissipation of energy by radiation. For the accele- 

 ration of one corpuscle is equal and opposite to that of the 

 other; hence the electric force in one pulse will be equal and 

 opposite to that in the other, so that when the pulse due to 

 one overlaps that due to the other the energy will be small. 

 The study of the positive rays in a discharge-tube shows, 

 however, that sometimes a rapidly moving corpuscle is 

 stopped and remains firmly attached to the atom when it 

 collides with it. In collisions of this kind the energy of the 

 corpuscle will be radiated away, and they may be regarded 

 as the chief source of the Eontgen rays produced when 

 cathode particles fall upon matter. That collisions of this 

 kind occur is shown by the fact that atoms travelling with 

 great velocity through a perforated cathode, and uncharged 

 when they pass through the cathode, on passing through 

 ionized gas at rest sometimes attract a corpuscle and become 

 negatively charged. The conditions are the same as if the 

 atoms were at rest, and the corpuscle moving with the velocity 

 of the atom and colliding against it, the impact resulting in the 

 stoppage of the corpuscle and its imprisonment by the atom. 



