208 



SOILS. 



near the surface within a variable time after a rain, or irriga- 

 tion, when the descending water column has attained a length 

 corresponding to the height to which the water would have 

 risen from below in a tube arranged as shown on p. 205. It 

 is therefore a condition of very frequent occurrence in the arid 

 region. 



Capillary Water held at Different Heights in a Soil Col- 

 umn. To determine the amounts of water held in the differ- 

 ent portions in columns of soils in which water ascends by 

 capillary rise, the following plan was adopted by the writer in 

 collaboration with Loughridge (Rep. Calif. Sta. 1892-4, p. 



99). 



Instead of glass tubes the soils to be tested were placed in 



copper tubes one inch in diameter, divided into segments six 

 inches long, and flattened on one side. In the flattened side a 

 slot half an inch wide was left, and glass plates, held in posi- 

 tion by rubber elastics, were cemented on the slotted side by 

 means of paraffin, to prevent a sifting-out of the soil. The 

 short sections can be connected at Uie ends like joints of stove- 

 pipe, and the earths can be easily introduced in proper, even 

 condition. It was thus possible to gain access to any portion 

 of the column at any time, for the taking of samples. 



WATER CONTENTS OF SOIL COLUMNS AT VARIOUS HEIGHTS ABOVE WATER LEVEL. 



Since gravity limits the capillary ascent in a progressive ratio, as 

 shown in diagram 39, it is obvious that the true maximum saturation 



1 This figure represents only a temporary condition ; the full height of 46 inches 

 was not reached until the I95th day. 



