302 On the Phcenomena of the Eledtophtirus', 



it does not show the whole amount of its superfluoag acqui- 

 sition til! removed, when the positive divergence greatly 

 increases. 



When the sole is insulated with the excited cake imposed, 

 the electrometer diverges as m the former instance, with 

 negative electricity. Now impose the cover, and the elec- 

 trometer connected with it indicates the negative electricity 

 strongly, because the attraction is most eager and powerful 

 at the upper or excited surface : the sole electrometer gra- 

 dually closes ; sometimes, however, coi>tinuing negative for 

 some time, and then opens with positive electricity. This 

 is precisely the state described by Mr. Brook in the act 

 of charging a 5,ar, both sides indicating a simila.r electricity: 

 the negative of the cover appears much stronger tlian the 

 positive of the sole, and, by making a cotcmporaneous com- 

 munication between the cover and sole^ a sensation is felt 

 in the thumb and finger resembling a shock. I am not, 

 however, satisfied that any actual charge takes place in these 

 circumstances : a charged insulated jar cannot be deprived 

 of its charge without offering a conductor to each side ; but 

 in this cas2 the shock is prevented by touching either the 

 sole or the cover separately when a spark passes ; and, on 

 completing the circuit, another spark, but no shock-like 

 sensation : the force of attraction being directed to the upper 

 surface, of course produces a disposition to receive the fluid, 

 or the negative state: the attractive force being diminished 

 at the sole releases a portion of the fluid which is disposed 

 to escape, and produces the positive slate. The sole and 

 cover being thus dift'erently disposed, one to receive and 

 the other to part with, if at the same moment the thumb 

 be presented to one side and the finger to the other, a double 

 spark will pass, and must occasion the sensation of a shock, 

 'i'he cover remains imposed, and in a negative state: on its 

 removal it changes and becomes positive; for, having iiad 

 its capacity enlarged by contact with the excited electric, 

 it holds, when iliat contact is removed, a superabundant 

 quantity : the attraction of the cake is redirected down- 

 wards, and the sole electrometer again becomes negative. 

 Replace thp. cover, preserving its insulation, and the states 

 are again reversed upon the same principles. Let a con- 

 ductor be now brought in contact with the cover; the sole 

 elcclrometer continues positive, and a spark passe? between 

 the cover and the conducting substance ; and so greedy is 

 the cover of tlic eiectric fluid, that the positive state is some- 

 times supcr-mduecd slightly; the cover, bv its communi- 

 cation with the grour;d, has rapidly obtained all the fluid 

 3 its 



