324 



ATMOSPHERIC ELECTRICITY. 



librium, it is moved horizontally toward these bodies. If the sky 

 is clear, there is observed a negative divergence, which reached 

 its maximum when the instrument had come under a tree, or as near 

 as possible to a building ; while it returned to zero every time it is 

 carried back to the place from which it started. This observation, 

 which appears to have been reported for the first time by M. Erman,* 

 may be explained by observing that when the electrometer was brought 

 into an equilibrium under a positive influence its stem remained in pos- 

 session of the negative electricity, which, repelled by that of the same 

 name possessed by the tree or building, produces the divergence which 

 is observed. 



The intensity of the electricity increases in proportion as we recede 

 from the surface of the earth. This increase was proved by the phi- 

 losophers who first engaged in this kind of research. De Romas, f 

 CavallOjJ and others obtained signs of electricity, the more powerful as 

 the kite which they used rose to a greater height. Science possesses 

 hitherto few data in respect to this fact. Schiibler sought to verify it 

 by observing the degrees of an electrometer, placed at increasing heights 

 on the side of a tower, so as to leave as nearly as possible the same 

 distance of five feet between its stem and the wall. The following 

 table shows the result of his experiments, which were made under a 

 clear sky, and at a temperature of 20° centigrade : 



Perpendicular height 

 above the srrouud. 



Degrees of the 

 electrometer. 



Observations. 



By a series of experiments made with a kite, the string of which 

 could at pleasure be connected with an electrometer or with a rhe- 

 ometer, M. Peltier§ discovered an important fact relative to the increase 

 respecting which he was inquiring. He observed that the electrometer 

 indicated an increasing positive electricity for 10 feet, while the first 

 indications of the rheometer did not take place except at a height of 

 131 feet. From 131 to 328 feet the needle moved feebly; but 

 beyond this height, even up to that of 810 feet, which was the 



« Journal de Physique, torn. LIX, p. 101. 1804. 



f Memoires des Savants Etrangers, tom. II, p. 406. 1755, 



% Traite complet d'Electricite, p. 294. 



P Journal de Schweigger, tom. IX, p. 351. 



^CoQjptes Eendus, torn. X, p. 712. 1840. 



