144 
Journal of Agricultural Research 
Vol. V, No. 4 
periods. The water was stirred occasionally to maintain uniformity of 
temperature throughout its mass. 
The temperature amplitudes employed are within 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 a>bout 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 Miami 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 allowing for the cold column all the 
soil that was contained in that cold section qf 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 t|ie 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 lines 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: 
(1) 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 
