450 Mr. cavallo’s Defcripfion of 
that the quickfilver in the long barometer-gage came as high as 
it flood at in a real barometer, and that the pear-gage indicated’ 
a degree of rarefaction about one thoufand. But as it was not 
known, whether the quickfilver had been boiled into the tube 
of the barometer, to which the long barometer-gage had been 
compared, therefore a barometer was accurately made for that 
purpofe. The glafs tube had been juft drawn at the glafs- 
houfe. It was perfectly clean ; the quickfilver was boiled in 
the whole length of it, and care was taken that the dimen- 
fions of the tube, ciftern, and divifons, were alike both in 
this barometer and in the gage. This done, the pump was 
tried again, and the quickfilver in the long gage rofe within 
one-twentieth of an inch of the quickfilver in the barometer,, 
or rather lefis, which thews that the air was rarefied little above 
600 times ; but at this time the pump was not in proper order 
for trying fuch nice experiments. It was leaky, and' had not been 
taken to pieces and cleaned for above fix weeks, in which time it 
had been frequently ufed, and continually left expofed to the 
duft of a working-fhop : yet it fhews, that in thefe unfavoura- 
ble circumftances this pump can rarefy the air above 600 times. 
Confidering all the above-mentioned circumftances and expe- 
riments, I think it may be concluded, that this pump, when 
in good order, can rarefy the air about one thoufand times. 
I fhall, laftly, conclude this paper with a liunmary account 
of feveral electrical experiments, which were made with this- 
pump ; referving to give a more ample and circumftantiaL 
account of them for another opportunity. 
When the air-pump was in good' order, a glafs receiver, - 
-which had a brals cap cemented to its upper aperture or neck, 
was laid upon the plate; then the end of the prime conductor 
of an elc&ric machine was placed within half an inch of the- 
cap 
