ATMOSPHERIC ELECTRICITY. 325 



maximum of height which the kite could attain, the deviation increased 

 so that the needle struck the check at 90°, and was maintained be- 

 tween 70° and 80°, consequently the current had at least a force of 

 600 proportional degrees of the electrometer. Thus, then, under a 

 clear sky the intensity of atmospheric electricity increased slowly 

 up to a certain height, beyond which it increased with very great 

 rapidity. Another fact, not less important, is the existence of a stratum 

 of negative air interposed between the positive strata, a fact which 

 M. Peltier observed when in the course of warm days light clouds 

 were formed. The reverse of the sign in atmospheric electricity 

 was exhibited for the first time April 21, 1840. The sky was quite 

 clear, except that here and there the vapor formed into long cirrus 

 clouds, which moved slowly from the south, while the lower wind 

 was from the northwest. The kite reached the height of 100 feet, 

 and the rheometer had as yet given no signs of a current, though 

 the electrometer had indicated an increasing positive tension at the 

 height of 10 feet. At from 100 to 1 64 feet the rheometer deviated from 

 2° to 3°, and indicated a descending positive current. Above this 

 height the two instruments remained an instant without giving any 

 electric sign, after which the rheometer indicated a descending current 

 of 2° or 3°, but negative. The electrometer assigned to this negative 

 zone a thickness of about 66 feet, above which the positive electricity 

 reappeared. The new positive current, of which notice was given by 

 the rheometer, was at first feeble ; but the kite being raised to 394 feet, 

 the needle began to move rapidly. When it had reached 590 feet, the 

 current showed 60°, corresponding to 160 proportional degrees. 



Some experiments on atmospheric electricity at different heights in 

 the air have also been made by Messrs. Becquerel* and Breschet, on 

 one of the plateaus in the vicinity of the Great St. Bernard, by 

 means of an arrow provided with a conducting wire, the extremity 

 of which communicated with a straw electrometer. The results at 

 which these philosophers arrived prove, 1. That on high mountains, in 

 clear weather, the electricity increases in intensity from leaving the 

 ground up to the height of at least 262 feet, the limit to which the 

 observations were carried ; 2. That this electricity always remains 

 positive, without any appearance of change of sign. 



We ought also to mention the experiments which Messrs. Gay 

 Lussac and Biotf made during their t\3rostatic ascension. These 

 philosophers likewise found atmospheric electricity increasing with 

 the height ; but it appeared to them negative, though the sky was 

 perfectly clear. This result is not surprising, if we consider that 

 the mode of experimenting adopted in this case consisted in suspend- 

 ing, by one end, a metallic wire of 164 feet long, terminated at the 

 lower end by a ball of metal, and that it was the electricity at the 

 top of the wire which was observed. This electricity would, then, be 

 of the same nature as that produced by a charged plate held over the 

 point or the ball of an electrometer; the point or ball would be 

 charged negatively by the positive induction of the plate. M. Biot* 



"' Traits de rElectricite et du Magnetisme, torn. IV, pag. 110. 

 j- Journal de I'hysiqiie, torn. LIX, pages 315 and 318. 



