142 



Journal of Agricultural Research 



ward and downward movement of moisture as the temperature grad- 

 ient changes diurnally. During the day, for example, the temperature 

 of the soil is highest at the surface and diminishes with depth; the surface 

 tension and the viscosity of soil moisture are lowest at the surface and 

 rise with depth; consequently, the movement of moisture should be 

 downward. During the night the reverse is true; the soil temperature 

 is lowest at the surface and increases with depth; the surface tension 

 and the viscosity of the soil water are greatest at the top and diminish 

 downward with increase of temperature; hence, the water translocation 

 should be upward. 



These considerations are a priori deductions from the laws of surface 

 tension and viscosity in their relation to temperature. Whether or not 



Fig. I. — Apparatus for determining thermal translocation of soil moisture when the column of soil lay 



horizontally. 



they are valid, however, has heretofore not been known, since there 

 appear to be no experimental data bearing directly upon the subject. 



With the object of obtaining this important and much desired in- 

 formation, an investigation of the problem was undertaken. The gen- 

 eral method of procedure consisted of placing soils of different but uni- 

 form moisture content in brass tubes 8 inches long and i K inches in 

 diameter, closing both ends with solid rubber stoppers, and keeping one 

 half of the soil column at a high temperature and the other half at a 

 low temperature for a certain length of time, then determining the per- 

 centage of moisture of the two columns and attributing any difference 

 in water content to thermal translocation. There were only two ampli- 

 tudes of temperature employed, o° to 20° and 0° to 40° C. — i. e., one 

 half of the soil column was kept at 0° and the other half at 20° and 



