30 BULLETIN 835, U. S. DEPARTMENT OF AGRICULTURE. 



A comparison of figure 4 with figure 2 shows very strikingly the 

 part gravity plays in capillarity. It shows to what extent gravity 

 aids or retards the movement of soil moisture by capillarity. An- 

 other striking feature is the comparative uniformity of the rate of 

 movement of the moisture after the first three or four days. While 

 there is a general slowing down of the rate at which moisture ad- 

 vances from day to day, it is so much less marked in these flumes 

 than in the flumes discussed in previous sections as to be of compara- 

 tively little moment. 



It is observed that after the first da}^ or two the type of soil used in 

 the flumes is of greater importance in limiting the extent of the move- 

 ment of the moisture. The more open and porous the soil, the more 

 rapid and extended the movement of the moisture. For instance, in 

 the sandy Idaho soil of flume 204, the moisture advanced as far in 

 one day as it would in the heavy Riverside soil in five and one-half 

 days and 50 per cent farther in the first clay than it would in the 

 heavy Whittier soil in 30 days. In flume 204 the only limit to the 

 extent of the movement of moisture was the ability of the wick to 

 furnish the moisture. However, the porosity of the soil is not the 

 only factor, but the transporting power of the soil itself is of prime 

 importance. For instance, comparing flume 34 (heavy Riverside) 

 with flume 74 (Upland), flume 34 has the greater rate of movement 

 of moisture at all times within the limits of the experiment, and yet 

 the soil of flume 74 has the greater porosity. The difference in the 

 rate of movement in these two soils appears to be due to the difference 

 in the capillary power of the wick to transmit the water from the 

 tanks to the flumes proper. Had there been less vertical lift from the 

 tank to the flume by the wick, flume 74 would undoubtedly have 

 shown the greater rate of moisture movement. The effect of porosity 

 is well illustrated in flumes 74 and 94. The soil in flume 94 has the 

 greater porosity, and while the rate of movement of the moisture is 

 less in this flume for the first week, it has the greater rate of move- 

 ment thereafter. Again, comparing flumes 4 and 34, the soil in flume 

 4 has the greater porosity, but the soil in flume 34 the greater capil- 

 lary power, and after the first two weeks the rate of movement of 

 moisture in flume 34 is greater. 



In table 17 is given the extent of movement of moisture as shown in 

 figure 4, in percentages of the extent of movement in flume 34. 



That is, in flume 34 the moisture had moved the first clay 26 inches, 

 or 100 per cent. In flume 4 the moisture had moved the first day 

 28.85 inches, or, as compared with the movement of moisture in flume 

 34, 111 per cent, while in flume 54 the moisture had moved 10.7 

 inches, or, based on the movement in flume 34, 41 per cent. Flume 34 

 maintained a relatively higher rate of movement of moisture than 



