4 BULLETIN 835, U. S. DEPARTMENT OF AGRICULTURE. 



remainder of the box filled with air-dry soil packed firmly against the 

 wet soil. The boxes were set either vertical or horizontal, no inclined 

 boxes being used. In the boxes set vertical, in some experiments, the 

 wet soil was placed at the top of the box and the air-dry soil was 

 placed at the lower end. In other boxes the wet soil was placed at the 

 lower end of the box and the air-dry soil at the upper end. Thus, 

 the movement of the moisture from the Wet soil into the dry soil by 

 capillarity would be, in some cases, with the force of gravity and, in 

 other cases, in an opposite direction. A few vertical boxes had the 

 middle section of the box filled with the wet soil, with the air-dry 

 soil at both ends, thus combining in the same box and at the same 

 time the upward and downward movements. 



The horizontal boxes were packed in the same way as the vertical 

 boxes with wet soil at one end and air-dry soil at tlie other. In a 

 few tests the middle section of the horizontal boxes was filled with 

 wet soil and air-dry soil placed at both ends. In a very few tests 

 the middle part of the box was filled with two sections of wet soil 

 containing different initial precentages of moisture and the dry soil 

 was placed at both ends of the box. 



METEOROLOGICAL DATA. 



In connection with the experiments a record was kept of the evap- 

 oration from a free water surface and a thermograph record taken 

 of the air temperature. Xo other meteorological data were recorded. 



SOILS USED. 



A uniform surface soil was selected for each set of experiments. 

 This soil was to be typical of a large area and was to be of a well- 

 known type. The soils were to be obtained from various parts of 

 the arid region that the data might be of general value. The greater 

 the number of types and the wider the range in types of soils used, 

 the greater the value of the tests. Uniform soils were to be used, as 

 the movement of moisture by capillarity varies in soils of different 

 types and the results obtained with mixed soils would be of little 

 value. 



INCIDENTAL EXPERIMENTS. 



The movement of soil moisture by capillarity within a soil of a 

 uniform type differs materially from its movement between soils 

 of different types. This difference is found in the rate and extent 

 of movement and. in the initial percentage of moisture necessary to 

 permit movement. To obtain some light upon this point a few 

 experiments were conducted. The general plan of these auxiliary 

 experiments was about the same as for the original experiments. In 



