382 Mr Wilson, Measurement of the Earth- Air Current, etc. 



the existence of penetrating radiations reaching the earth's surface 

 from cosmical sources, the coexistence of low values of the radiation 

 Avith low values of potential gradient is what might be expected, 

 as the upper layers would be exposed to more intense radiation 

 than the lower (for we must suppose that there is considerable 

 absorption in traversing the atmosphere) ; the variation in 

 ionisation would thus be greater above than below, and the 

 potential gradient and radiation would thus vary together. 



If the existence of a penetrating radiation from cosmical 

 sources were established it would be of the greatest importance 

 in connection with atmospheric electricity. For it would open 

 the question as to whether the negative charge of the earth might 

 not be supplied by these rays. At present I think it is much 

 more likely that precipitation will prove to be a sufficient source. 



