42 



THE THEORY OF IONIZATION OF GASES 



18. Agreement between experiments and theory. 



To illustrate the theory the experiments 1 may be 

 quoted in which the currents between two parallel plates 

 in air at one millimetre pressure were determined, the 

 electric force being 350 volts per centimetre in each 

 case. The distance between the plates I is given in 

 centimetres in the first line of Table XII. ; the second 

 line gives the charge q acquired by one of the plates 

 while the light was acting on the negative electrode for 

 a fixed time ; the third and fourth lines give the values 



of J* and 



respectively, where a =5* 25 



and /3=-0141. 



a 



The values of e agree only with the experiments at 

 the shorter distances, but the numbers in the fourth 

 line show that the positive ions (although /3 is small 

 compared with a) produce an appreciable effect when 

 the plates are about 6 millimetres apart and have a very 

 large effect for larger distances. 



TABLE XII. 



1 See papers in Electrician, April 3, 1903, and Philosophical 

 Magazine, November, 1903, on "The Genesis of Ions by the 

 Motion of Positive Ions in a Gas." 



