On Evaporation. 583 
twice have seen it at 62°: in changeable and 
windy weather it is liable to considerable fluc- 
tuation; but this is not the place to enlarge 
upon it. 
For the purpose of observing the evaporation 
in atmospheric temperatures I got two light tin 
vessels, the one 6 inches in diameter and 3 inch 
deep, the other 8 inches diameter and 3 inch 
deep ; and made to be suspended from a balance, 
like the former one. When any experiment 
designed as a test of the theory was made, a 
quantity of water was put into one of these 
(generally the 6 inch one, which I preferred) 
the whole was weighed to a grain; then it was 
placed in an open window or other exposed 
situation for 10 or 15 minutes, and again weigh- 
ed to ascertain the loss by evaporation; at the 
same time the temperature of the water was 
observed, the force of the aqueous atmosphere 
ascertained as above, and the strength of the 
current of air noticed. From a great variety of 
experiments made beth in the winter and sum- 
mer, and when the evaporating force was strong 
and weak, I have found the results entirely con- 
formable with the above theory. The same 
quantity is evaporated with the same evaporating 
force thus determined, whatever be the temper- 
ature of the air, as near as can be judged; but’ 
VOL. V. Lk 
