STUDIES I.V ATMOSPHERIC ELECTRICITr. 



EFFECT OF RAIN. 



When the rain is moderate and the drops fine, the potential keeps 

 very low positive values with only slight variations. When a down- 

 pour takes place with sufficient violence, the potential becomes at once 

 negative, and exhibits very irregular and energetic variations. As 

 soon as the violence of the rain diminishes, the potential regains its 

 positive value. (See Fig. 6.) These phenomena can all be explained 

 in accordance with Lenard's investigation on the electricity of 

 waterfalls.'' Lenard prt^ved by a series of the most conclusive experi- 

 ments, that when a stream of pure water falls upon a metallic or 

 other conductors previ(3usly moistened, the water droplets splashing 

 in all directions become positively, and the air near them negatively 

 electrified. There is no difficulty in applying this result to explain 

 the negative potential in the case of a steady down-pour of rain. The 

 summer rain gives sometimes a positive as well as a negative potential 

 with violent variations. This is no doubt due to the proper charge 

 of the rain drops, whose formation is probably something different 

 from that in the case (;f the usual cyclonic precipitation. Usually a 

 peal or two of thunder will be heard on such an occasion. 



1) Lemrd, Wied. Ann. 46. ISQ-J. 



