452 Mr. cavallo’s Defcription of an improved Air-Pump. 
not intirely vanifh ; which fhews, that the eleCtric fluid, which 
proceeded from the conductor to the cap of the receiver in the 
form of fparks, did not pafs to the earth ail through the con- 
ductor, by which the cap was made to communicate with the 
ground ; but part of it went at the fame time through the 
vacuum, fo that when the pump in this experiment was infu- 
lated, fparks could be drawn from the plate of it. 
Having repeated the above mentioned experiments with only 
this variation, viz. that the extremity of the prime condu&or 
was put in contaCt with the cap of the receiver, the appearances 
of eleCtric light within the receiver were very nearly the fame 
as in the preceding experiments ; but if now the cap of the re- 
ceiver was made to communicate with the ground, the light 
within the exhaufted receiver vanished intirely, though the 
cleCtrical machine aCted very vigoroufly. 
When a pith-ball electrometer was fufpended within the re- 
ceiver from its brafs cap, and fome electricity was communi- 
cated to the outflde of the laid cap, its balls diverged very little 
when the air within the receiver was rarefied about ioo times ; 
their repulfion was hardly difcernible when the air was rarefied 
about 300 times j but in a greater degree of rarefaCtion they did 
not diverge in the leaf!, and that was the cafe whether a fmall 
or a large quantity of eleCtric fluid was communicated to the 
cap of the receiver. 
June 24, 1783. 
1 
