54 BULLETIN" 835, U. S. DEPAKTMEXT OF AGRICULTURE. 
lated from this formula agree with sufficient accuracy with the ob- 
served values of y. 
Dr. Loughridge states that the limit of moisture movement was 
reached at the end of 195 days at 50 mches. It is interesting to note 
that the position of the moisture at the end of one year as calculated 
from the formula would be 56.2 inches ; at 390 days, twice the time of 
observation, 57 inches : two years at 66.2 inches ; and three years, 72.9 
inches, or only 22 inches above what it was at the end of 195 days. 
OPEN VERSUS COVERED FLUMES. 
The results obtained from the covered flumes are very similar to 
those obtained from the flumes open on top to evaporation. With one 
or two exceptions the results with the covered flumes do not differ 
materially from what could have been foreseen from the results with 
the open flumes. The essential difference is one of degree, as would 
have been expected. One striking exception is the fact that in every 
instance of the 25 or 30 experiments the open flume has the more 
rapid rate of movement of the moisture for the first one to five weeks 
of the experiment, the difference in time depending upon the char- 
acter of the soil. The heavier the soil and the longer the open flume 
maintained the more rapid rate of movement of the moisture. The 
more rapid rate of movement is maintained irrespective of evapora- 
tion. This fact will be more clearly seen from the data submitted 
below. There is, as would be expected, a small difference in the rela- 
tive percentages of moisture contained in two flumes, and especially 
is this difference noticeable in the upper layers of soil. 
Inasmuch as the results with the covered flumes differ only in de- 
gree from those of the open flumes, it is not deemed that the sub- 
mission of all the data and its discussion would add materially to the 
value of this report. For that reason there will be discussed only 
one covered flume in its relation to its comparable open flume. The 
two flumes that will be presented in detail are the horizontal flumes 
70 and 71 containing the soil from Upland. This is a gravel and 
sand soil containing but little clay. The selection of this particu- 
lar soil for presentation is merely for convenience, as the results 
obtained by its use are similar to the results obtained from other soils, 
figure 3 (p. 23) shows the curves representing the movement of 
moisture in these two flumes. * 
Table 38 gives the total movement of moisture in these two flumes 
at the end of various periods of time. From this table it will be 
observed that flume 70, which is open to evaporation, has the more 
rapid rate of movement of the moisture up until the fifth day. After 
the fifth day flume 71, or the covered one, has a more extended move- 
ment of the moisture and upon the thirtieth day this difference is 
