Proceedings of the Polytechnic Association. 917 



frequently these fires resemble, more or less, the brush, as of electri- 

 city in motion ; but it sometimes happens that the light is concen- 

 trated into small globes, without any trace of diverging jets. These 

 are, doubtless, of electricity in the opposite direction, or negative. 

 But it is not only at the extremities of objects at the surface of the earth 

 that luminous appearances are perceived in times of storms ; some- 

 times fog, rain, snow and hail are decidedly luminous ; but it is snow 

 which most frequently presents this phenomenon, which is now taken 

 as unquestionably due to electricity. The elecitric property of snow 

 is so decided that atmospheric electrometers are sometimes power- 

 fully charged during a tall. According to Beccaria, a cloud' charged 

 with snow, diffused in all directions a reddish light, sufiiciently 

 intense to enable one to read books printed on ordinary type. Fre- 

 quently, people, in the midst of a storm, become foci of electricity, 

 which is not only manifest by a light, but by a particular whizzing 

 noise. 



Brewster cites the case'of two English travelers who, surprised 

 in their descent of Etna, b}^ a heavy fall of snow, accompanied by 

 violent claps of thunder, heard a hissing noise every time they 

 extended their arms into the air ; and on extending a finger and 

 moving it through this snowy atmosphere, in various directions and 

 with rapidity, they were able, at pleasure, to generate a great variety 

 of musical sounds, the intensity of which was such that they were 

 perfectly heard at the distance of several yards. 



I shall endeavor to show, presentl}-, that aurora Ijorealis is a phe- 

 nomenon similar in its essential character to those above 'cited, and 

 that all are due to what has been called atmospheric electricity. 



Causes of Atmosphekic Electkicity. 



Many hypotheses have been propounded to explain the origin of 

 Atmosplieric Electricity. Some have ascribed it to the friction of the 

 air against the ground ; some to the growth of plants, or to the evapor- 

 ation of water ; some have compared the earth to a vast voltaic pile ; 

 others to a thermo-electric apparatus. Some of these causes, and per- 

 haps all, may concur, in some degree, in producing the phenomena. 

 According to the theory of Peltier, the " electrical phenomena of the 

 atmosphere are entirely due to the induction of the earth, which is 

 primarily and constantly negative." 



It is difficult for me to conceive how the earth should be rendered 

 thus constantly negative, unless there be some force, constantly in 



