62 BULLETI2T 835, XL S. DEPARTMENT OF AGRICULTURE. 



at least as great as 15°, then it would have the condition of the 

 flumes above described. If, now, there were a sudden change in the 

 slope of the ground toward the horizontal, or if the more loamy soil 

 verged into a denser soil, free water might be developed at this point 

 as the result of capillary action. 



The capillary siphon might develop, also, in an earthen reservoir 

 dam with a puddle or concrete core wall extending only to the flow 

 line or slightly above it, and under certain conditions produce satura- 

 tion in the lower side of the dam. 



That a capillary siphon as above described is in accord with 

 physical laws and was not the result of mechanical defects of error 

 in manipulation is readily proven. Briggs (13) and Widtsoe and 

 McLaughlin (19) have shown that the quantity of water retained by 

 a soil column against gravity depends upon its length. Also that 

 a column 1 foot in length will hold at all points a greater percentage 

 of water than a column 2 feet in length. Hence, as the length of the 

 inclined flume is greater, the percentage of moisture held against 

 gravity will be smaller. It would follow, therefore, that beyond a 

 certain length of the inclined part of the flume, not all of the water 

 furnished by the wick could be retained against gravity by the in- 

 clined part of *the flume. 



It has been shown in this report that the distribution of moisture 

 in vertical soil columns does not decrease uniformly with height 

 above water. It has been indicated also that the greatest percentage 

 of moisture in the vertical column may not be at the immediate water 

 surface. From moisture analyses made of samples from vertical 

 flumes, noted in this report, and from a great many other special 

 experiments, the writer will say that the greatest percentage of mois- 

 ture in a vertical soil column with its lower end in water may be 

 and frequently is at an appreciable distance above the water. From 

 these data and as the result of tests by the writer and others, it can 

 be said that a vertical soil column can take up by capillarity from a 

 body of free water more water than it can hold against gravity, if 

 the free water be removed from the bottom of the soil column ; that 

 is, if the vertical tube is filled with soil and the lower end placed in 

 a vessel of wafer and allowed to stand for a month or longer and the 

 water is then removed from the tank, a part of the moisture in the 

 soil column will drain out. To repeat — a vertical soil column will 

 take up by capillarity from a body of water more moisture than it 

 can retain when the source of the water is removed. In view of the 

 above statements and the recorded experiments, it appears that capil- 

 lary siphons may occur in nature, as the result of physical laws. 



