132 DRY-FARMING 
ANNUAL ANNUAL 
Pace ape aa yee Ratio 
(INcHEs) (IncHEs) 
El Paso, Texas . . ? 9.23 80 8.7 
Fort Wingate, New Mexico 14.00 “80 5.7 
Fort Yuma, Arizona... 2.84 100 35.2 
Phoenix, Arizona... . 7.06 90 12.7 
Tueson, Arizona . . . . 11.74 90 7.7 
Mohave, Califonia . . . 4.97 95 19.1 
Hawthorne, Nevada .. . 4.50 80 17.5 
Winnemucca, Nevada... 8.51 80 9.6 
St. George, Utah . . . . 6.46 90 13.9 
Fort Duchesne, Utah . . . 6.49 75 11.6 
Pineville, Oregon . . . . 9.01 70 7.8 
Lost River, Idaho . . . . 8.47 70 8.3 
Laramie, Wyoming .. . 9.81 70 7.1 
Torres, Mexico . . . . . 16.97 100 6.0 
To understand the methods employed for check- 
ing evaporation from the soil, it is necessary to review 
briefly the conditions that determine the evapora- 
tion of water into the air, and the manner in which 
water moves in the soil. 
The formation of water vapor 
Whenever water is left freely exposed to the air, 
it evaporates; that is, it passes into the gaseous 
state and mixes with the gases of the air. Even 
snow and ice give off water vapor, though in very 
small quantities. The quantity of water vapor 
