Evaporation in a Current of Air. 425 
humidities are not greatly different. If the velocity of the air current 
were alone in question, we should have expected that the second column 
would have contained a loss of some 3|- grains greater than the first 
column. Since it is considerably less than this — only 1*6 grains — the 
inference to be considered is that vapour is passing off from the water 
surface more rapidly at first when warm water is used than when the 
stationary temperature is attained. This is what would have been 
expected. 
The following values are derived from an experiment — the only one 
I have as yet been able to make — upon the comparative, simultaneous 
rate of evaporation from warm water and from water first cooled to its 
final temperature. Four gauges were used in pairs, one gauge with warm 
and one with cold v\^ater, placed side by side at a distance of 15 inches 
from the fan ; one with warm and one with cold water at a distance 
of 33 inches. 
Dry bulb 64-0° 
Dew-point 42*0 
Humidity, per cent 45 
Current velocity, 13 inches from fan per minute 884 ft. 
n n 31 „ ,, 668 ,, 
15 inches from Fan. 
33 inches from Fan. 
Initial temperature of water . . . 
59-8° 
71-2° 
60-0° 
71-2° 
Final 
59-8 
59-6 
60-0 
60-1 
Loss by evaporation, grains ... 
36-8 
51-2 
30-4 
40-0 
If we assume that these results may be expressed by the formula — 
E = A (T - ^) 0 {lu), 
which is Fitzgerald's simplified formula, and calling E,^ the evaporation 
from the warm water, and E^ the evaporation from the cold water, we 
shall have, by division — 
_ T^, — ^ 
• E^ He - t 
Now, at the distance of 15 inches from the fan, E,, = 51*2, E,, = 36-8, 
Tg = 0*514, t = 0-267. Substituting these values in the formula, we get — 
T,, = 0-611 inch. 
