Jan. 3,1916 
Hourly Transpiration Rate on Clear Days 
59i 
The mean values are plotted in figure 2. It should be recalled that 
all transpiration measurements in 1912 were made in the hail-screen 
inclosure (PI. UV, fig. 1). The radiation measurements were likewise 
made under this screen, which reduced the radiation about 20 per cent 
(Briggs and Shantz, 1914, p. 3). It should also be borne in mind that 
during the year of 1912 the solar radiation outside the inclosure was 
about 20 per cent lower than normal (Briggs and Shantz, 1914, p. 54). 
The mean solar radiation shown in the first curve of figure 2 is relatively 
symmetrical, as would be expected if clear or only slightly cloudy days 
Fig. 2.—Composite transpiration graph o! wheat and environmental graphs for corresponding period. 
are chosen. The maximum radiation is reached at 12 o’clock, noon, 
and amounts at that time to only 0.80 calories per square centimeter 
per minute. The gradient is steep during the early morning and late 
afternoon, but there is little change in the radiation intensity during the 
midday hours. 
The second graph in figure 2 gives the hourly air temperature in degrees 
Fahrenheit. The temperature reaches its minimum, 55 0 F., between 4 
and 5 a. m., and its maximum, 86° F., between 2 and 3 in the afternoon. 
The average temperature from noon to midnight is much higher than 
from midnight to noon. 
The transpiration is recorded in grams per hour. It will be seen from 
the graph in figure 3 that the transpiration during the night is almost 
negligible. A marked increase is recorded at 6 o’clock in the morning. 
