^8o Mr. cavendish’s Account of 
when the water boils vehemently than when it boils 
gently; and if the mouth of the chimney is covered by 
any light body, in fuch manner as to leave no more paf- 
fage for the fleam than what is neceffary to prevent the 
body from being blown off by the preffure of the in- 
cluded vapour, the thermometer will Hand only half or 
three quarters of a degree higher, if the ball is immerfed 
a little way in the water, than if it is expofed only to the 
lteam. But if the covering of the chimney is removed, 
the thermometer will immediately fink feveral degrees, 
when the ball is expofed only to the Beam, at leaf; if the 
cover does not fit clofe; whereas when the ball is im- 
merfed in the water, the removal of the covering has fcarce 
any effect upon it. Whence it appears, that the lteam of 
water boiling in a veffel, from which the air is perfectly 
excluded, is a little but not much cooler than the water 
itlelf, but is confiderably lb if the air has the leaft admif- 
lion to the veffel. Perhaps a ftill more convenient 
method of adj ulting the boiling point would be not to 
immerfe the ball in the water at all, but to expofe it only 
to the fteam, as thereby the trouble of keeping the wa- 
ter in the veffel to the right depth would be avoided;: 
and belides, feveral thermometers might be adjufted at 
the fame time, which cannot be done with proper accu- 
racy when they are immerfed in the water, unlefs the 
diftance of the boiling point from the ball is nearly the 
fame in all of them. At prefent there is l’o little uni- 
formity obferved in the manner of adj lifting thermome- 
ters, that the boiling point, in inlh uments made by our 
3 bell 
