Mr. Daniell on Evaporation. 51 
‘Temperature, Loss 
Pressure Beginning Eud Grains 
ee ee ee ee 
es See ee en Me ee 
ea as ee a ee ee 
ete. ae ee er ae eee 
ae ae a | ee 
ce eae, Cee a eee ot ene 
es ee ts ee ee ee 
When the exhaustion was pushed to the utmost, the gauge stood 
at 0°07, and the evaporation in the half hour was 87:22 grains. 
During this last experiment, the water was frozen in about eight 
minutes, while the thermometer under the ice denoted a tempera-~ 
ture of 37. 
Now, before we infer from these experiments the state of evapo- 
ration, from different degrees of atmospheric pressure, it is neces- 
sary to apply to the results a correction for the variation of tem- 
perature which took place during their progress. The quantity of 
evaporation having been determined to be in exact proportion to 
the elasticity of the vapour, we must estimate the latter from the 
mean of the temperatures before and after the expcriments, and 
calculate the amount for any fixed temperature accordingly. This 
will, doubtless, give us a near approximation, although, from the 
last experiment, we perceive that the method of estimating the tem- 
perature of the surface water cannot be absolutely correct. The 
following table presents us with the former results so corrected for 
the temperature of 45°: 
Pressure, Grains. 
E12: Mem PE 1°24 
LE i RTE RET aN 6 
7°6 . . . . 5:68 
3°8 . . . . 9°12 
1:9, Sie Pie pale FRC u/s (piep, 
96 ve), bolaiin ds 298d 
Lf OS NE «Lae 
sted ane het Oe 
