THE FORMS OF SOIL WATER 225 



face of the former column. King^ shows this by the 

 following data : — 



Evaporation from the Surface of Sand Columns of Dif- 

 ferent Lengths, their Base being in Contact with 

 Free Water 



Length of Colttmn in Inches 



Evaporation at Sitrface 

 IN Inches a Day 



6 

 12 

 18 

 24 

 30 



.114 

 .111 

 .080 

 .034 

 .019 



Briggs and Lapham^ found, in comparing the evapo- 

 ration from tubes of different lengths (85 and 165 centi- 

 meters, respectively) of Sea Island soil, that the shorter 

 column showed over five times as much evaporation in a 

 period of forty-two days. This diminished flow with the 

 thinner films is a vital point in plant production, since 

 wilting must occur as soon as capillary movement becomes 

 too sluggish to supply moisture fast enough for normal 

 development. 



The thickness of film is important also in a considera- 

 tion of the height of rise in dry and moist soil respectively. 

 It is evident that the rate would be much more rapid in 

 the latter, but what as to total rise? Stewart,^ in study- 



1 King, F. H. Principles and Conditions of the Movements 

 of Ground Water. U. S. Geol. Sur., IQth Ann. Kept., Part II, 

 p. 92. 1897-1898. 



2 Briggs, L. J., and Lapham, M. H. Capillary Studies. 

 U. S. D. A„ Bur. Soils, Bui. 19, pp, 24-25. 1902. 



3 Reported by Briggs, L. J., and Lapham, M. H. Capillary 

 Studies. U. S. D, A., Bur. Soils, Bui. 19, p. 26. ,1902. 



