ELECTRICAL ORIGIN OF RAIN, DEW, ETC. 303 



reject from their leaves ! Most probably the 

 non-conducting properties of snow, by prevent- 

 ing the dangers of excessive cold to plants, are 

 those to which its serviceable reputation is 

 chiefly due. It is, however, very certain, that 

 snow contains proportionably more ammonia, 

 and probably more carbonic acid, than rain- 

 water. 



There can be no doubt now, that electricity 

 plays a most important part in these aqueous 

 phenomena of the atmosphere. Humboldt 

 writes " In fogs, and at the beginning of 

 falls of snow, I have, in the course of a long 

 series of observations, seen the previous per- 

 manently vitreous " (or positive) " electricity, 

 change suddenly into the resinous " (or negative) 

 " electricity ; and these alternate repeatedly, 

 as well in the plains of the frigid zone as under 

 the tropics in the Paramos or Alpine wilder- 

 ness of the Cordilleras, between ten and twelve 

 thousand feet high. The alternate transition 

 was in all respects similar to that which the 

 electrometer had shown shortly before during 

 the continuance of a thunderstorm." Mr. Of. A. 

 Rowell, in a communication laid before the 

 British Association in 1847, states his convic- 

 tion, that most of the phenomena of evapora- 

 tion, rain, hail, and even of the winds of 

 temperate regions, are due to electricity. He 



