44 BULLETIN" 835, U. S. DEPARTMENT OF AGRICULTURE. 



points to become more uniform in outline as the experiment con- 

 tinues for longer periods of time. That is, the line joining the points 

 representing the position of the moisture on the thirtieth day is 

 more regular and uniform than is the line joining the points for the 

 position of the moisture on tire first day. The figure indicates that 

 with the lapse of an extended period of time the line joining the 

 points representing the extreme extent of moisture would be of a 

 parabolic form. This curve would have a rather limited extent in 

 the vertical direction upward, but the longitudinal extent and the 

 extent downward from the vertical might be infinity. Even with 

 evaporation a factor, these last two named distances are relatively 

 very great as compared with the vertical elements. The drawing 

 emphasizes and portrays more clearly than do the figures the im- 

 portance of gravity in the movement of soil moisture by capillarity. 

 These deductions are of importance from the economic point of view 

 in that they show very clearly what may be the distribution of mois- 

 ture within the soil of water applied upon sloping ground. It in- 

 dicates, for instance, that the extent of distribution of moisture down 

 a slope would be much greater than it would be up a slope. A com- 

 parison of the data for these flumes indicates how great would be the 

 loss of water in conveying channels through capillary action where 

 the conveying channels traverse ground having a transverse slope. 

 These data would indicate that on the lower side of the channel cap- 

 illary action would continue taking water from the channel in 

 about the same quantity for an indefinite period of time, while on- 

 the upper side the loss of water through capillarity would be very 

 much less in quantity and in extent of time through which it would 

 act. These figures indicate further the importance of slope of the 

 strata of alluvial soil, both in reference to conveying channels and 

 impounding reservoirs. In other words, these data indicate that 

 with any appreciable slope downward of the strata, capillary action 

 continues indefinitely. 



WATER USED. 



In considering the quantity of water used by the several flumes 

 from the vertical upward to the 45° downward from the horizontal, 

 it is found that the inclination of the flume is a most potent factor 

 in determining the quantity of water that will be removed from the 

 tanks. The data for these flumes indicate clearly the effect of gravity 

 in the movement of water as soil moisture by capillary action. A 

 difference in inclination may mean, and most frequently does mean, 

 a difference between practically no movement of soil moisture and a 

 movement of an appreciable relatively constant quantity of water. 



The figures within the small circles in figure 6 give in liters the 

 quantity of water removed from the tanks. 



