188 
IOWA ACADEMY OF SCIENCE 
A number of theoretical formulae have been proposed for the computation of 
evaporation from freely exposed water surfaces the general form of which is 
the simple one given by Dalton 
E = A (a-b) (1 + ck) 
where the argufnents A,c,K are the temperature of the water surface, the dew 
point of the atmosphere and the movement of the wind, a and b being the dry 
and wet bulbs. Carpenter from Ft. Collins .in 1887 proposed the following, which 
is of this form; 
E,inch-day=0.3868 (e^— e j, ) (l+0.0025w), 
where w is the wind movement per day in kilometers. The constants suggested 
here apply satisfactorily only to local conditions and are not general. 
The author hopes in another year to offer a formula that shall be satisfac- 
tory for the Iowa river conditions but is not prepared to do so at the present 
time. 
