306 Discharge of Electricity through Argon and Helium. 



take the average of the ratios of successive readings (coupled 

 by lines in the tables). 



The mean ratio of conductivities thus found from the first 

 set of experiments was 



1 : 1-07. 

 From the second set 



1 : 1-00. 



The mean of all these experiments gave as the ratio of the 

 conductivity in cell No. 1 to that in cell No. 2 



1 : 1-04. 



Cell No. 2 was then attached to a mercury-pump and 

 exhausted. Helium was admitted to atmospheric pressure. 

 The cell was then carefully readjusted to exactly its original 

 position. 



The deflexion produced by 10 seconds' exposure to the rays 

 for each of the cells alternately was noted. 



Air (cell No. 1). Helium (cell No. 2). 



32 3^-15 



The ratio of conductivities from this last set of experiments 

 is 1 : *4(>. Other experiments gave results very nearly the 

 same. But in no other case was the radiation quite so steady. 

 I prefer therefore to rely on the above. 



Correcting for the inequality of the cells, the ratio is 1 : *44. 



It follows that the rate at which ions are produced in 

 helium is about half that at which they are produced in air. 



General Remarks. 



The peculiar interest of the gases argon and helium is in 

 their monatomic characters. 



The view is now generally taken that the electric discharge 

 is conveyed in all cases by ions, these ions being produced by 

 a dissociation process of some kind. If this be admitted 

 there can be no escape from the conclusion that the ions of 

 monatomic gases are split up into something smaller. 



The above experiments make it sufficiently clear, I think, 

 that these gases convey the discharge in a normal manner. If 

 the potential-fall at the cathode is a measure of the energy 

 expended in the ionization of the gas when effected by an 



