426 
Transactions of the Boyal Society of South Africa. 
At a distance of 33 inches from the fan, = 40, E, = 30*4, T, = 0-518, 
t = 0-267. Whence— 
= 0-597 inch. 
The respective ratios, therefore, are in fair agreement, and correspond 
to an average temperature of 64° or 65° in the warmer water. The 
results in this case probably compare better with Fitzgerald's than any 
other that I have hitherto been able to obtain, and for that reason I hope 
to be able to make a series of experiments on similar lines. 
A fact that stands out more clearly the more closely the subject is 
examined is that it is useless to attempt to deduce the true law of 
evaporation from the meteorological averages of extended periods, that 
is to say, by comparing the various elements of evaporation, average wind 
velocity, average temperatures of air, water, and dew-point, &c., over a 
day, or week, or month. These elements change so irregularly and 
so continuously that only short periods of time are admissible. It is not 
perhaps wandering far from the truth to say that under natural con- 
ditions a stationary state of affairs is never attained to ; on the contrary, 
the temperature of the water always lags considerably behind what it 
would be if it could keep pace with the air temperatures, and its 
" personal equation " in this respect is greater as the mass of water 
is greater. 
