﻿3GG Dr. G. Owen and Mr. J. H. T. Roberts on the 



Fie. 4. 



300 



£J00 



100 



-^ J. 



10 20 



AGE OF CLOUD IN SECONDS. 



^ 



Before the age of 4 seconds, however, the curve exhibits 

 certain irregularities, which are probably the joint effect of 

 the following processes going on in the ionization-chamber 

 immediately after the formation of the cloud : — ■ 



(a) Rapid replacement of the ions caught by the cloud. 



(b) Partial diselectrification of the charged cloud by the 



action of the ionizing rays. 



(e) Thinning of the cloud by the evaporation of drops too 

 small to be in equilibrium. 



(d) Settling of the cloud. 



Now the curve shows that in 06 of a second the current 

 rises to within a few percent, of, say, a 5 second cloud value. 

 Since an expansion of 1*331 catches practically all the ions, 

 it is evident that the replacement of the ions occurs very 

 rapidly. Since, further, the settling of the dense cloud takes 

 place only very slowly, we must regard the shape of the 

 curve for the cloud at ages between 1 and 3 seconds as being 

 mainly due to a combination of (/>) and (c) above. We 

 propose testing this point further, varying the conditions as 

 regards intensity of ionization and density of cloud. 



