622 Mr. nairne’s Account of 
the preffure on the furface of the quickfilver in the 
ciftern, and in the tube of the long barometer-gage, was 
diminifhed to about a three-hundredth part : the pear- 
gage being now pufhed down till its open end was im- 
merfed under the furface of the quickfilver in the cup, 
the air was then let in, and the pump appeared by that 
gage to have exhaufted all but a fix thoufandth part of 
the air; or, in other words, the degree of exhauftion by 
this gage appeared to be fix thoufand times. 
Finding (till this difagreement between the pear-gage 
and the other gages, I tried a variety of experiments ; but 
none of them appeared to me latis factory, till one day in 
April 1776, fhewing an experiment with one of thefe 
pumps to the honourable henry cavendish, Mr. 
smeaton, and feveral other gentlemen of the Royal 
Society, when the two gages differed fome thoufand 
times from one another, Mr. cavendish accounted for 
it in the following manner. “ It appeared,” he faid, 
“ from fome experiments of his father’s, Lord charles 
“ cavendish, that water, whenever the preffure of the 
“ atmofphere on it is diminifhed to a certain degree, is 
“ immediately turned into vapour, and is as immediately 
“ turned back again into water on reftoring the pref- 
“ fure. This degree of preffure is different according to 
“ the heat of the water: when the heat is 72 0 of faii- 
“ renheit’s 
