634 Mr. C. T. R. Wilson on 



layer, and, what is still more important, the cloud itself from 

 base to summit during the time that the liffhtninff-discharffes 

 were taking place was never 2,500 metres in height : thus 

 supersaturation to a fourfold degree could not possibly have 

 taken place. 



To sum up the discussion, we may state that the following 

 six reasons have been given for considering the theory, first 

 proposed by Wilson, and subsequently expanded by Gerdien, 

 unsatisfactory as an explanation of the electrical effects 

 connected with thunderstorms. 



A. Electrical. 



(1) The theory does not account for the frequent lightning 



discharges observed during thunderstorms. 



(2) It cannot account for the large charges of electricity 



carried down by rain during thunderstorms. 



(3) It is extremely improbable that any electrical separa- 



tion would take place as the result of water vapour 

 being condensed from fourfold supersaturated air 

 onto negative ions. 



B. Meteorological. 



(4) An extensive stratum of supersaturated air could not 



form above an ascending current. 



(5) Even if such a stratum were once formed it could 



not exist after precipitation commenced from the 

 condensation layer above it. 



(6) The meteorological phenomena observed during 



thunderstorms do not lend any support to the 

 theory. 



Simla, Nov. 11, 1908. 



LYI. On Thunderstorm Electricity. 

 By C. T. R. Wilson, M.A., F.R.S.* 



MR. SIMPSON has been kind enough to send me a 

 copy of his paper ; ' On the Wilson-Grerdien Theory 

 of Thunderstorm Electricity." 



I should like at the outset to remark that I have nowhere 

 myself attempted to account for the strong electric fields of 

 thunderstorms by the theory which Mr. Simpson attributes 

 to me. I have merely regarded condensation on negative 

 ions as one of the possible factors in the production of such 

 fields. 



* Communicated bv the Author. 



