an Improved Air-pump , &c. 451 
cap of the receiver ; fo that when the machine was in action, 
the electric fluid in the form of fparks went from the con- 
ductor to the brafs cap, and when the receiver was exhaufted, it 
palled from the cap to the plate of the pump through the re- 
ceiver, illuminating its whole cavity. The more per fed the 
vacuum was made, the better condudor of electricity it be- 
came, and the electric light was more equably diffufed in it ; 
but it became by no means faint, even when the receiver was 
exhaufted to the utmoft, though the light changed appearance 
according as the receiver was more or lefs exhaufted. Thole 
appearances were as follows. 
Degrees of rarefadion as fliewn 
by the fliort gage. 
Appearances of the eleftric light within the 
receiver. 
Air rarefied 40 times.. 
80 
100 
400 
Light in large, long, but divided,, 
it reams. 
Fine diffufed light, of a white co- 
lour. 
Beautiful diffufed light inclining to 
red or purple, and filling the 
whole receiver. 
When the gage fhewcd A diffufed light, filled equally every 
the utmoft degree of part of the cavity of the jar. It 
exhauition. had hardly any reddifh hue. 
In this date, or even when the air within the receiver was 
rarefied not above 100 times, if the brafs cap of the receiver 
was made to communicate with the ground by means of good 
conductors- in perfect contact, the light within the receiver 
occafioned by the electric fparks given by the prime conductor 
to the cap of the receiver was thereby diminifhed, but it did 
not 
