ee a 
On Evaporation. — 589 
Solution. Subtract the observed evaporation 
from that opposite the given temperature in the 
table; and look above for the number nearest 
to the remainder in the same column of evapor- 
ation, opposite to which will be found the force 
of the aqueous atmosphere, and the point at 
’ which it begins to be condensed. , 
Example. Finding the evaporation from a 
vessel of 6 inches in diameter to be 1. 7 grain 
per minute with a brisk wind, air 62°; what is 
the weight of the aqueous atmosphere, and the 
‘temperature at which it begins to be condensed 
into water ? ; 
The number opposite 62° in the third column 
of grains is 3. 52, being the whole evaporating 
force at that temperature in a perfectly dry at- 
mosphere; from which take 1.7 grains, the 
real evaporating force observed, and the remain- 
der, 1. 82, corresponds, as per table, to the 
force .294 inches of mercury, the weight of 
vapour, and to 43° of temperature*, 
* It may be proper to remind the reader that all the 
experiments on evaporation are understood to be madé 
in the open air, or ina window with a current inward 5 
also it may be observed the evaporation in a close room 
is much less and is besides irregular, being greater pro- 
portionably from a less surface, evidently from the stag- 
~ nation of the air, 
