18 THE THEORY OF IONIZATION OF GASES 



or if the experiments be examined it will be noticed that if 

 a' corresponds to a force X' and a pressure p r , then at a 

 pressure zp', the value of a will za! when the force is 

 *X', z being any multiplier. 



In the later experiments the pressures were chosen so 

 as to show this by inspection. 1 Thus, with air at a 

 pressure of 1 millimetre and a force of 350 volts per 

 centimetre, a=5'25 ; at 2 millimetres pressure and 

 with a force of 700 volts per centimetre, a=10*5. 

 Another example may be taken from the experiments 

 with hydrogen : 



p=S mm., X=1050 volts per cm., a=14*8 

 p=4: mm., X= 525 volts per cm., a= 7*4 

 p=2 mm., X= 262 volts per cm., a= 3'7 



The results of all the experiments for any one gas can 

 therefore be recorded by a table of values of a/p and X/p 

 or by means of a curve 2 representing one of these ratios as 



a function of the other -=/*( ). 

 p J \pJ 



9. Agreement between the experimental results and 



the equation -J ( 



It is easy to see that the theory requires that this 

 relation should exist between the variables a, X, and p. 



In passing through a centimetre in a gas an ion 

 traverses free paths of various lengths between the 

 collisions. The chance of producing a new ion by 

 collision will depend on the velocity at impact, and this 



1 Many examples may be found in the researches published in 

 the Philosophical Magazine, November, 1903, and December, 1904. 



3 This result was first obtained from the experiments with 

 Eontgen rays. See Philosophical Magazine, February, 1901. 



