On certain Cases of Electrolytic Decomposition. 37 



overcome the resistance of the ascending air. Part of the 

 charge is thus lost, but the part is smaller the more powerful 

 is the ascending current. There is, moreover, a continual 

 replacement, owing to uninterrupted condensation. 



With very.fine rain, which at once falls to the earth, power- 

 ful charges will scarcely be expected. Much depends, in any 

 case, on the rapidity of the formation of clouds and rain. The 

 rain which falls from a cloud must have the opposite electricity 

 to the cloud, and can of course act by induction on a second 

 cloud which it traverses, and which also rains. 



Moreover, after each flash of lightning the remainder of the 

 electricity will soon attain a maximum if the rainfall is suf- 

 ficient, and the contraction in volume which is inseparable 

 from it. 



The essence of this theory is that the electricity of thunder- 

 clouds acts by induction, and that the thunder-cloud is a self- 

 acting duplicator. The rain which falls from it plays the 

 part of the jet of water in Thomson's drop-accumulator, while 

 the increase of potential is occasioned by the enormous con- 

 traction of volume and surface. 



This theory may claim over preceding ones the following 

 advantages : — 



(1) It enables us to regard the cloud as an aggregate of 

 discrete drops of water. Hence a charge imparted to a cloud 

 does not spread by conduction, but as soon as the cloud begins 

 to rain spreads from point to point by induction. 



(2) It does not require electrification by friction. It is not 

 impossible that friction may give the start ; but this becomes 

 unimportant in the further progress of the phenomenon. 



If it should come out, and a number of experiments we have 

 tried do not allow us to settle the point, that a production of 

 electricity by the friction of water-spray or rain against water 

 or ice cannot be experimentally proved, the presence of 

 atmospheric electricity is sufficient to start the phenomenon. 



(3) The theory finds the equivalent of the work expended, 

 in the establishment of a difference of potential, in the vis viva 

 of the falling drops of water. 



VI. On certain Cases of Electrolytic Decomposition. By 

 J. W. Clark, Assista?it Professor of Physics in University 

 College, Liverpool** 



THE atomic or molecular conditions which determine me- 

 tallic or electrolytic conduction are of great interest, but 

 seem as yet too obscure to allow T of any definite general conclu- 



* Communicated by the Physical Society ; read May 23, 1885, 



