_- 2°. 
sO 
-On Evaporation. 577 
the humidity previously existing in the atmos- 
phere, all other circumstances the same. 
The objects in view in this essay, are, 
1. To determine the precise effect that a 
variation of temperature has upon the quantity 
evaporated, 
2. To determine the ratio of evaporability 
ef different fluids, 
3. To find a rule by which the quantity and 
effect of previous humidity in the air may be © 
ascertained, 
4. From these and other facts to obtain a 
true theory of evaporation. 
On the Evaporation of Water at 212°, 
I took a small cylindrical vessel of tin, its 
diameter 3i and depth 2} inches; and having 
fixed three pieces of wire to equidistant points 
of the circumference, they were fastened together 
at the top and the extremities bent into a hook, 
by which the vessel might be suspended from 
the end of a balance, &c. This done, the vessel 
was nearly filled with water, which was then 
made to boil over a‘small red fire in different 
circumstances: it was held in the hand and 
yemoved nearer to or further from the fire, so as ta 
