144 Journal of Agricultural Research voi. v,ko.4 



periods. The water was stirred occasionally to maintain uniformity of 

 temperature throughout its mass. 



The temperature amplitudes employed are ^^-ithin the upper limit of 

 the diurnal amplitudes of temperature at the upper depths in the soil, 

 but they are too high for the range of temperature that exists at any 

 one time between the various adjacent depths. 



The duration of each experiment was about eight hours. This time 

 limit was calculated to represent approximately the length of period 

 that the day and night soil temperature gradient is most marked. 



The effect of temperature on the movement of moisture in soils of 

 uniform moisture content was investigated in five diverse classes of soil: 

 Miami light sandy loam, ]Miami heavy sandy loam, [Miami silt loam, 

 Clyde silt loam, and jMiami clay. Each soil contained a large number of 

 different moisture contents. These various moisture contents in each 

 soil ranged from very low to very high. 



To procure a very uniform moisture content throughout the soil column, 

 each soil, after it was moistened to the desired degree, was passed 

 through a sieve and then mixed thoroughly. It was then placed in the 

 tubes and packed uniformly by allowing the tubes to fall in a vertical 

 position from a certain height a definite number of times. 



At the end of each experiment the warm column was separated from 

 the cold column of soil by means of a spatula. This was done by draw- 

 ing out all the soil from that warm section of the tube which extended 

 up to the plane of the partition and allomng for the cold column all the 

 soil that was contained in that cold section of the tube up to the other 

 plane of the partition, and also that portion of the soil contained in the 

 tube under the hole of the partition. This last part of the soil was 

 accorded to the cold column of soil because its temperature is inter- 

 mediate between the opposite temperature extremes, and it was desired 

 to make the line's of demarcation between the two columns" of soil as 

 prominent and distinct as possible. The moist soils were dried in an 

 electrical oven for about 20 hours at a temperature of 105° C, and the 

 percentage of moisture content was calculated on the dry basis. The 

 weights were always determined on a sensitive chemical balance. 



The fact has been mentioned that the movement of moisture from 

 a warm to a cold column of soil was studied in two different ways-. 

 (i) When the column of soil lay horizontally and (2) when it stood 

 vertically. The data obtained from both series of experiments show 

 that if the same percentages of moisture were employed practically the 

 same results would be obtained, no matter whether the soil columns 

 remained in the horizontal or vertical position. For the sake of brevity 

 and simplicity of presentation, therefore, only the results of the series 

 of experiments wherein the soil column was held in the vertical position 

 will be presented here. These experimental data, together with their 

 diagrammatic representations, are submitted below. Table II gives the 



