DRY-FARMING 



become a sort of stretched elastic film 

 under molecular attraction; and this is 

 what happens to the soil films under the 

 action of surface tension. 



Now, if very fine capillary glass tubes 

 are dipped into water, the water will rise 

 up the tubes in inverse proportion to their 

 diameters, or, in other words, the smaller 

 and thinner the tubes the higher will the 

 liquid rise. Again, if the bottom of a 

 tube containing soil is placed in contact 

 with water the moisture will be drawn up 

 one, two, three, or even more feet, de- 

 pending upon the nature and the fineness 

 of the soil. The movement of film water 

 is usually referred to as "capillary ac- 

 tion," and it was formerly supposed that 

 this moisture passed upward to the sur- 

 face by means of capillary or hairlike 

 tubes. In reality, there are no such tubes, 

 merely fine passages, pores, or capillary 

 channels, and the film water rises from 

 72 



