NATURAL PHILOSOPHY. 



ATMOSPHERIC ELECTRICITY. BY JAMES P. ESPY. 



IT has not yet been ascertained by electricians, so far as I know, what is 

 the cause of atmospheric electricity ; those, however, who have studied my 

 tlicoiy of storms, and agree with me that there is an upmoving current of 

 air in the centre of all storms, kept up by constant evolution of latent caloric, 

 as the vapor condenses by the cold of diminished pressure as the air ascends 

 with its vapor in it, will agree with me that it follows as a corollary from the 

 following experiments, that electricity must be generated simply by the up- 

 moving current of air from the surface of the earth, especially if it be 

 violent enough, as it frequently is, to carry up drops of rain with it to a 

 great height. 



It is well known that all bodies, as Dr. Alex. Palagi, of Bologne, says, in 

 their natural state, give signs of positive electricity; when separating from 

 the soil, and of negative, when approaching it. In the twenty-third volume 

 of Geneva Archives of Science, pp. '28'} and 382, it is stated that Yolpicclli 

 caused a ball of metal to revolve on a horizontal axis of glass, at a distance 

 from that axis one metre and a half, and connected by means of a copper 

 ribbon with a Volta's condenser, during a demi-revolution ascending, de- 

 taching it when descending, and in ftnir demi-rcvolutions he collected 

 positive electricity enough to make the straws diverge so as to touch the 

 interior sides of the electrometer. 



When the connection was made with the ball descending, negative elec- 

 tricity was obtained. 



Xow, in all storms, especially where floods of rain descend, there arc at 

 the sides and under those parts of the cloud where floods of rain descend, 

 down-moving currents of air; and this will account for the sudden change 

 of electricity, from positive to negative, so well known to all observers. 

 Moreover, as there are thousands of up-moving currents of air every day, 

 nearly all over the earth, this theory will account for the upper air being 

 almost always positively electrified ; for a body cannot be removed upwards 

 from the surface of the earth without becoming positively electrified; and, 

 vice versa, a body cannot descend towards the surface without becoming 

 negatively electrified. It would be well to examine the electric state of the 

 air in the belts of high barometer, where the air must in general be descend- 

 ing, and also in the annulus of storms, where the barometer stands above the 

 mean (and of course the air must be descending there), to see if the electricity 

 is not sometimes negative; and if so, electricity may become a means of 

 predicting storms. Jour. Franklin Institute. 



