.90 



ON THE ELECTRIC COLUMN, 



conacquently of the pile) ; since each part may cliange from 

 positive to negative, or inversely, according to circumstances, 

 by the different motions impressed on the electric Jluid; 

 which motions may be concluded from these phenomena 

 themselves, but will be directly perceived in the folio-wing 

 experiment. 



Ej^kS. Exp. Q. a necessary condition of this class of experi- 



ments is, that the state of the ambient air be such, that 

 alternately, at each extremity of the column, one of the gold 

 leaves strikes the side of the electroscope, and at last sticks 

 at one of the extremities. The following are three different 

 cases in these phenomena. 



1, When the strikings are alternate at the extremities, 

 these instantaneous communications of the column with the 

 ground at each side, by the contact of the gold leaf with the 

 tinfoil, produce in the former a Jlux and rejiux of electric 

 Jluid. When the gold leaf strikes at the cupper extremity, 

 some fluid ascends from the ground into the column, and 

 repairs the deficiency on this side; but this additional quan- 

 tity of electric fluid in the column occasioning a striking at 

 the zinc extremity, the new quantity o^ fluid returns that 

 way to the ground. These rises awd ebbs of the electric 

 fluid in the column are observed at the middle electroscope, 

 but only when bome time elapses between the strikings; for, 

 on account of the slowness of motion of the fluid, directly 

 shown above, when the strikings rapidly alternate, before 

 one of the effects has extended itself in the column, the 



Cause of the contrary effect begins; in the same manner as the rise and 



want of tides ^^^ ^f ^},g water are not sensible within the Mediterranean^ 



intheMcditor- i i ir. »• • r i • 



raneanandBal- •^^'^ 'i'ld the Baltic, on account or their narrow entrance; 



*•*• for before the ^?U' has extended itself some way up these 



seas, the reflux operates in the contrary direction. But 

 these mo/ioH6' of the electric fluid are very sensible at the 

 middle paint, m the following cases. 



i. When the gold leaf comes to adhere at the copper ex- 

 tremity, thus placing it in a continued communication with 

 the ground, tjje strikings, which become more frequent at 

 the zinc side, produce a pulselike stream of the electric 

 fluid in the column, manifested by the motions of the gold 

 leaves ia the middle electroscope : their divergence is positive^ 



the 



