CIRCULATION OF GROUND WATER. 421 



under certain conditions. In an experiment carried on for forty days in 

 coarse sands, in which the free surface of water was 15, 30, 45, 60, and 75 

 cm. below the surface, King found that the mean evaporation per day was 

 0.2895, 0.282, 0.203, 0.0864, and 0.0495 cm., respectively.* In the cases of 

 the largest and the smallest numbers, those in which the level of ground 

 water is 15 and 75 cm. below the surface, the amount of evaporation in a year 

 would be 105.6675 and 18.0675 cm., respectively. "Where the movement is 

 vertically upward through a distance of 1 foot [30 cm.] it has been found 

 by experiment that the rate for a fine sand was 2.37 pounds per square foot 

 [1.16 grams per sq. cm.] per day of twenty-four hours; when the lift was 

 increased to 2 feet [60 cm.] the movement became 2.07 pounds [1.01 grams 

 per sq. cm.]; at 3 feet [90 cm.] it was 1.23 pounds [60 grams per sq. cm.], 

 and at 4 feet [120 cm.] only 0.91 pounds per square foot [0.444 gram per 

 sq. cm.]. A similar trial with medium clay loam gave a movement of 2.05 

 pounds [1 gram per sq. cm.] for a lift of 1 foot [30 cm.], 1.62 pounds 

 [79 grams per sq. cm.], for 2 feet [60 cm.], 1 pound [0.488 gram per sq. cm.] 

 for 3 feet [90 cm.], and but 0.9 pound [0.439 gram per sq. cm.] where the 

 lift was 4 feet [120 cm.]." 



"The observations show that it [capillary movement] is very rapid at 

 4 feet [120 cm.]; so rapid, indeed, that were it maintained throughout the 

 year it would deliver at the surface the equivalent of 63.85 inches [11.2 

 cu. cm. per sq. cm.] of water." 6 With finer but equally porous soils the 

 amount of water thus derived from below the level of ground water may 

 be considerably greater. 



By "capillary movement,' 1 as used by King, is meant the process, 

 already described, of creep along the walls to the surface above the free 

 surface of ground water, not the raising of the surface in consequence of 

 capillarity, as that term is ordinarily used. (See pp. 150-152.) 



Cultivation greatly retards the process of the upward movement of 

 water by molecular attraction. The upper part of the soil is in blocks 

 separated by supercapillary openings. The continuous capillary openings 

 in the soils and the close contacts are broken up. The amount of wall 

 area upon which the water may creep upward is greatly reduced. The 

 conditions prevent molecular attraction from readily bringing water to the 

 surface, and evaporation is retarded. The intense heat from the sun during 



"King, cit, p. 92. & King, cit., p. 85. 



