fome Experiments made with an Air-pump. 639 
gage’s indicating a greater degree of exhauftion than the 
barometer-gage : but what to fuppofe could poffibly 
make it indicate a lefs,! was entirely at a lofs; for after 
having made thefe furprizing, experiments on the vitrio- 
lic acid,. I wiihed once more to try if I could repeat, with 
the lame refult, fome of my former experiments, in 
which the pear-gage had indicated fo nearly the fame 
degree of exhauftion as the barometer-gages. Accord- 
ingly I took away the vitriolic acid from under the re- 
ceiver; the pump was then frefh oiled, and I was very 
eareful to wipe clean and dry the receiver and pump- 
plate, and then cemented down the receiver as ufual. 
EXPERIMENT £l. 
The pump was then worked, and the degree of ex— 
hauftion appeared by the barometer-gage to be 43 2, ; but 
by the pear-gage to be but 370. 
I know of no circumftance attending this experiment 
that differed from thofe in which my former experi- 
ments were made when' the gages agreed fo nearly, un- 
lefs it were that of the weather : 1 recoiled; that it was* 
then very damp,, and now it had been very dry for fome 
time. How this circumftance could make fo great an 
alteration in the refult of thefe experiments,! cannot pre- 
tend 
