14 
COLORADO EXPERIMENT STATION. 
EVAPORATION. 
§ 18. The following table shows the amount of evaporation 
that has been observed from our standard tank during the past 
eleven years. The tank is of galvanized iron, three feet square, origi- 
nally two feet deep, but since 1889, three feet deep. During the 
summer months, the height of the water is measured by the hook 
gage to the nearest thousandth of a foot, twice daily. After Septem- 
ber, darkness interferes with the observation at 7 p. m. and readings 
are made only at 7 a. m. After ice forms the tank is undisturbed 
except at the beginning of the montu. The ice is then loosened 
from the sides of the tank, and the elevation of the water 
surface, which is then the same as if the floating ice were melted^ 
is measured. Ice sometimes forms of considerable thickness, 
and punctures in separating it from the sides have caused the loss 
of the record for several months. The rainfall is measured by stand- 
ard gages near the tank. The amount given as the evaporation, is 
the loss from the water surface after allowing for the rainfall, or is 
the fall of the surface plus the rainfall. The amounts here given 
are subject to slight corrections, as critical examination may cause 
the rejection of some days of heavy showers. 
TABLE IV.— EVAPORATION FROM WATER SURFACE. 
Tank 8x3x3 feet, flush with fjronnd, at Fort Collins, Colorado. Elevation 4.990 feet above sea 
level : latitmle 40° 34'. longitude 10.5°. Amounts are given in inches. 
Jan. 
Feb. 
Mar. 
April 
May 
June 
July 
Aug. 
Sept. 
Oct. 
Nov. 
1 Dec. 
Year. 
1887 
2.46 1 
t 3.23 
4.60 
5 . 55 
5.19 
5.75 
5.23 
4.24 
4.12 
3.26 
1.48 
1 1.60 
46.71 
1888 
1 .... 
4.45 
7.7Ut 
7.00t 
4.06 
3.94 
2.17 
1.35 
.99 
1889 
i'.08 1 
1 1 03 
2‘75 
4.06 
3.72 
4 34 
5.20 
5.15 
5.19 
3.28 
.62 
1.42 
37.84 
1890 
.86 1 
2.36 
3.48 
3.. 50 
4.32 
5.71 
5.44 
5.76 
3.69 
2.71 
1..32 
1.10 
40.25 
1891 
1.891 
1.90 
2.23 
2.24 
5.03 
4,97 
5.72 
4.9i 
4.12 
3 62 
1.74 
1 
39.12 
1892 
2 51 
! 
2.78 
3.58 
3.49 
4.20 
4.69 
5.64 
5.11 
3.33 
1.93 
1.13 
40.54 
1893 
p. 
1 1.52* 
3.79 
5.40 
5.12 
6.12 
6.41 
4.73 
5.04 
3.79 
1 05 
1.38 
1894 
1.14t 
1 1.15t 
1.95 
4.61 
4.66 
5.01 
5.74 
4.88 
3.77 
3.75 
1.64 
1.22 
39.52 
1895 
l.l9t 
! 1.19t 
D 
4.91 
4.27 
4.13 
4.57 
4.52 
4.06 
2 24 
1.53 
1 1.68 
1896 
2.64 
2.25 
2:39 
4.71 
5.91 
5.09 
5.23 
5 80 
3.34 
2.94 
1.62 
•1.25 
43.17 
1897 
1.80 
2.20 
p. 
3.33 
,4.13 
4.26 
4.64 
4.76 
3.97 
2.88 
1.47 
.94 
Average. ... 
1.73 
1 
1.90 
3.00 
4.19 
4.57 
5.21 
5.44 
4.95 
4,21 
3.09 
1.43 
1.22 
' \ 
40.94 
1 
* Record from part of month, 
t Deduced from loss in two months. 
+ From record from February 17. 
p. Tank punctured, record Jacking. 
§ 19. As the temperature of the water is an important factor 
in the amount of evaporation, the average temperature of the water 
for the corresponding time is given in Table 5. The temperature 
given is the mean of the surface temperatures at 7 a. m. and 7 p. m. 
The maximum and minimum temperatures at the surface have also 
been taken by self-recording instruments in the water in early spring 
or late fall. Their record is not so complete and is not given here. 
The average derived from the 7 a. m. and 7 p. m. observations, as 
shown by hourly readings, is lower than the average temperature of 
the tank by about 3.5°. The diflerence is due to the fact that while 
