

Electricity of Atmospheric Precipitation. 9 



easily accounted for by the electricity brought down by the 

 rain. 



It is more difficult to determine how much breaking of 

 drops would be necessary to give the charge found on the 

 rain. For this we ought to know the charge on the drops ; 

 but so far this is entirely unknown. The next approxima- 

 tion is to know the charge on a c.c. of rain-water. This also 

 is practically unknown for non-thunderstorm rain. From a 

 very few observations Schindelhauer concludes that it is about 

 *5 E.S.U. per c.c. This, however, is too high a charge, for 

 it would mean that about 80 per cent, of the "Landregen" 

 he investigated fell at a rate of only *4 mm. per hour, which 

 is unlikely. Probably the mean charge on non-thunder- 

 storm rain is about '1 E.S.U. per c.c. Now the best 

 observations made on the electrification produced by break- 

 ing drops of water are those of J. J. Nolan *, who found 

 that charges up to 1*36 E.S.U. per c.c. could be given to 

 water by breaking it into very fine spray. 



This indicates that if about 1/10 of the rain was broken 

 up once into fine drops the observed charge would be pro- 

 duced. Future observations must decide whether this 

 amount of breaking does occur, at present we can only say 

 that quantitatively the theory is not impossible. 



These considerations lead to the conclusion that with non- 

 thunderstorm rain the si on of the charge on the rain and the 

 reversal of the field are explained by the theory, the only 

 outstanding question is whether there is sufficient breaking of 

 drops during light steady rain to give the charges observed. 



Snow. — Very few observations on the electricity of snow 

 have been made, the chief being those of the writer in Simla t 

 and those of Schindelhauer in Potsdam J. 



At both Simla and Potsdam the snow was sometimes 

 positively and sometimes negatively charged, and on occa- 

 sion the snow proved to be very highly charged. In one 

 important respect the results from the two stations were 

 opposite. In Simla the snow brought down a large excess 

 of positive electricity, while at Potsdam the excess, also 

 large, was negative. 



The chief objection brought against the theory based on 

 the electrification through the breaking of drops has been 

 that it cannot explain the electrification of snow in which 

 there are no drops to break. But there is with solids the 

 exact counterpart of the phenomenon with liquids. AVhen a 

 drop breaks the liquid takes a positive charge and the air a 



* Nolan, Proc. Kov. Soc. A. xc. pp. 531-543 (1914). 



t Simpson, Proc. Roy. Soc. A. lxxxiii. pp. 402-403 (1910). 



| Loc. cit. 



