fame Experiments made with an Air-pu np. 635 
r 
Degrees of exhauf- 
tion according to 
f 
Barom. 
g a g e - 
Pear- 
gag 9 . 
exp. xl v. The pump was then worked as ufuai, — 
Exp. xlvi. The lail experiment repeated with another n 
common pump, the leathers of the piftons of which > 
were alfo foaked in water, — • — J 
37 
34 
38 
37 
From thefe experiments it evidently appeals, that the 
air-pump of otto guericke, and thofe contrived by 
Mr. gratorix, and Dr. hooke, and the improved one 
by Mr. pappin, both ufed by Mr. boyle, alfo hauks- 
BEe’s, s’gravesande’s, muchenbrook’s, and thofe of all 
who have ufed water in the barrels of their pumps, could 
never have exhaufted to more than between 40 and 50, 
if the heat of the place was about 5 7 ; and although 
Mr. smeaton, with his pump, where no water was in 
the barrel, but where leather fcaked in a mixture of water 
and fpirit of wine was ufed to fet the receiver on the 
pump-plate, may have exhaufted all but a thoufandth or 
even a ten thoufandth part of the common air, according 
to the teftimony of his pear-gage; yet io much vapour 
muft have arifen from the wet leather, that the contents 
of the receiver could never be lefs than a feventieth or 
eightieth part of the denfity of the atmofphere : never- 
thelefs, it does not feem that any deficiency in the con- 
ftru&ion of Mr. smeaton’s pump was the caufe of his 
4 N 2 not 
