ATMOSPHERIC ELECTRICITY. 295 



inch in diameter, the height being an inch and a half. Its 

 cover of ivory does not project above the glafs, and is per- 

 forated in the middle with a hole in which a fmaller glafs tube 

 is fixed, and through this laft tube partes the metallic rod that 

 ferves to fufpend the gold leaves, and is upon the whole five 

 feet in length, being compofed with feveral pieces fcrewed 

 together, in order that they may be more eafily conveyed 

 from place to place by feparating them. A divergence of 

 three lines in thefe leaves anlwers to two lines in the elec- 

 trometer of Volla ; and that degree of electricity which would 

 produce a divergence of two lines and a half in this laft, 

 caii fes the leaves of Mr. Weifs to touch the fides of the glafs 

 cylinder. 



Mr, Erman walked in the fields with his electrometer, Whenraifed 



having its rod confined to the length of three feet. When he fudde 'y l * 



° diverges fluu 



iuddenly raifed it from the ground, he obferved a ftrong 



divergence of plus electricity. When he lowered it with 

 the fame fwiftnefs, he perceived an equal great divergence 

 of minus. The point of a fixed metallic rod of much greater 

 length, erecled at the fame fpot, did not give the leaft indica- 

 tion of electricity. 



An electrometer placed on a poft of three feet in length, If flowiy raifed it 

 produced no divergence; and, when it was afterwards (lowly £ oes "°^ dlver S e j 

 raifed one foot, or a foot and a half, it likewife afforded no fuddenly de- 

 iign ; but when it was very quickly brought down to the poft, P reffedlt diverges 

 it exhibited minus electricity to fuch a degree, that the gold 

 leaf touched the fides of the glafs. This charge was gradually 

 difperfed in the air, or by touching the electrometer with the 

 hand* ; but by raifing the inftrument with equal fpeed above 

 the poft, a divergence of plus electricity of the fame ftrenglh 

 was afforded which was deftroyed in the fame manner. 



The more inlulating the air the lefs it is neceftary to raife Conducing 

 the electrometer in order to produce this effed; but the longer P ower of the ™ 

 the point, the more ftrikingly will the effed be (hewn, even re f u i t3t 

 in damp weather. A circular motion at a conftant diftance 

 above the earth does not exhibit any electricity, neither does 

 a progreflive motion upon level ground afford any change j 



* From this fa& it appears, that the ele£trometer had not any 

 flips of metal within the tube like thofe of Bennet, who firft ufed 

 gold leaves. N. 



but 



