28 
COLORADO EXPERIMENT STATION. 
§36. We may dismiss the losses from seepage from considera- 
tion. They depend upon the character of the site and nothing in 
the mere elevation would increase or diminish the seepage, unless the 
lower temperature of the soil should lessen the rapidity of seepage, 
and this, as shown in Bulletin 33, may be considerable. In 
general the rock strata are nearer the surface in the mountains and 
more attention may well be given to the geological characteristics of 
the site. 
§ 37. But elevation has an influence on evaporation, and as 
evaporation is shown to be of more importance in the cases examin- 
ed, the effect of elevation on losses will be principally due to its ef- 
fect on evaporation. 
§ 38. The factors controlling evaporation, are : 
First — The temperature of the surface of the water, which in- 
dicates the limit of the amount* of vapor which the air in contact 
with the water will absorb. 
Second — The amount of moisture present in the air. The dif- 
ference between the moisture corresponding to the temperature of 
the water surface, and the moisture actually present, is a measure of 
the additional amount of vapor which the air will take up. 
Third — The wind movement. 
§ 39. The temperature of the air is decidedly lower at high ele- 
vations, though on individual days inversions may occur, and the 
air be warmer at the high elevations. This is often shown in com- 
paring the observations taken at the College, with those taken by 
Mr. C. E. Lamb at the foot of Long’s peak. This inversion occurs 
principally in the winter months, between November and April, and 
has less effect on evaporation than if occurring in the summer. 
Taking the records from several places, we find the average 
temperatures as follows, where the lower temperature with increased 
altitude is to be noted : 
Latitude. Elevation. Av. Temp. 
Agricultural College, Ft. Collins.- 40° 34' 5,000 ft. 47°. 7 
Denver 39° 45' 5,300 ft. 49°.5 
Colorado Springs _.38° 50' 6,100 ft. 47°. 2 
Lamb’s, near Long’s Peak 40° 20' 9,100 ft. 37°. 0 
Pike’s Peak 38° 50' 14,147ft. 19°.4 
The difference of 8,000 feet in elevation between Colorado 
Springs and Pike’s peak, causes a difference of 28° in mean annual 
temperature, equivalent to a difference of 1° for 300 feet rise. 
§ 40. The temperature of bodies of water freely exposed to the 
air will not differ much from that of the air in contact with them. 
The temperature of the water surface averages higher than the whole 
body of water, because as the water warms, the heated layers remain 
on top for temperatures above 39°, while in cooling the water sinks 
as it cools and the whole mass cools together. Below 39° the colder 
