56 
BULLETIN 835, U. S. DEPARTMENT OF AGRICULTURE. 
of the experiment. This can be accounted for in two ways: First,, 
all evaporation could not be eliminated without liability of trapping 
the air within the flume. Second, there is, as has been shown 
previously, an increase in the percentage of moisture contained in 
different portions of the flume with the age of the experiment. 
Table 41 gives the use of water by these flumes in equivalent depth 
over an area equal to the cross section of the flumes. 
Table 40. — Water required 
at various times to ad- 
vance moisture an aver- 
age distance of 1 inch. 
Table 41. — Water removed 
from tanks at various 
times, in depth. 
Flume. 
Fiumo. 
Number 
of days. 
Number 
of day?. 
70 
71 
70 
71 
c. c. 
c. c. 
Inches. 
IwJus. 
1 
259 
231 
1 
3.66 
3.66 
5 
288 
291 
5 
7.32 
7.32 
10 
311 
310 
10 
10.37 
10.37 
15 
328 
3-21 
15 
12.81 
12. 81 
20 
371 
326 
20 
15. 86 
14. 64 
30 
412 
333 
30 
20. 13 
17. 69 
It is found that flume 70 used the equivalent of 20.13 inches of 
water in 30 days, while the covered flume (71) used the equivalent of 
17.69 inches or about 12J per cent less than the open flume. These 
figures show that for the last ten days of the experiment the open 
flume used 4.27 inches and the closed flume 3.05 inches or a little over 
25 per cent less water than the open flume. These last figures would 
represent the effect of evaporation. In other words, during the last 
ten days of the experiment evaporation from the flume took care of 
at least 25 per cent of the water furnished by the wick. 
EFFECT OF TEMPERATURE ON SOIL-MOISTURE CONDITIONS. 
As has been stated previously, a temperature at and below the 
freezing point appears to have influenced to a marked extent the dis- 
tribution of moisture within the flumes. Some few soil samples taken 
from the flumes during the winter of 1916-17 gave results contrary 
to what was to be expected. In the sampling of the flumes, two 
samples were taken from each point of sample. The soil from the 
top 5 inches was placed in one bottle and the soil from the bottom 
5 inches in a second bottle and the moisture determined for each 
separately. There are two basic reasons why the percentage of mois- 
ture in the top samples should be less than that in the samples from 
the bottom 5 inches. First, the sample from the upper 5 inches 
