<2g(5 ATMOSPHERIC ELECTRICITY. 



but when the ground rifes even infenfibly, the phenomenon 

 is obferved, and it is rather extraordinary, that it even affords 

 a means of afcertaining the level, 

 Variations of the To vary the experiment, the electrometer may be placed 

 experiment. u p Qn a j qw f n pp 0rtj an( j touched with an infulated flick or 

 wire which has been quickly moved towards the ground, and 

 is afterwards raifed with the fame quieknefs. The elec- 

 trometer in the fir ft cafe exhibits phis electricity, and in the 

 fecond minus. 



It is very remarkable, that the minus electricity paffes 

 through Zero before it changes into plus, and vice verj'a, ac- 

 cordingly as the instrument is raifed or lowered even when 

 there is no interval between the two motions; but the diver- 

 gence will be more vifible, if time be allowed for the elec- 

 trometer to difcharge itfelf between the two experiments. 

 Sauflure's obfer- Sauffure formerly obferved the eftential requifites in this 

 vations. phenomenon; but his electrometer was not fo fenfible, and 



he explained the phenomenon by fuppofing that the elec- 

 trometer was the moft infulated, and the fixed rod not fuf- 

 ficiently fo to indicate fuch flight degrees of electricity. 

 The electrometer Mr. Erman has afcertained, that the phenomenon muft 

 is affefted not by b e attributed to the manner in which the electricity is diftribut- 

 the atmofphere, ec ^ ' n bodies. The mafs of the ground exerts its influence 

 but {imply by the very fenfibly to a certain difiance, and the electric atmofpheres 

 **~th which an- a ^ l, P on eacn other without any intervention of the air. The 

 pears to poffefs infulated metallic rod which we raife from the ground by 

 the minus ftate. folding it perpendicularly, undergoes no other change than 

 is owing to its own proper electricity, which is then lefs com- 

 penfated by the influence of the ground. Whether the elec- 

 trometer or the plate of an eleclrophorus be flowly raifed, 

 the electricity becomes communicated to the furronnding air, 

 The termination and is not manifefted. A ball placed on the point of the rod 

 of the conductor Q f ^ e electrometer does not at all change the divergence of 

 endofedV glafc, the leaves; and even when the conducting rod of the elec- 

 mak.es no dif- trometer is encloied in a lube of glafs not open at the top, 

 the phenomena are the fame, and the divergencies of plus 

 and minus are equally feen according to the direction of the 

 motion. And when a iecond tube is put over the firft, tor 

 the purpofe of more exactly preventing the contact of the air, 

 the refults are not at all changed. 



3 Mr. 



