Relation of Nonavailable Water to Hygroscopic Coefficient 23 
found soon after its application to be prostrated, but they re- 
covered when it was removed. Thus the windows were left with- 
out protection against the direct rays of the sun. As a result 
the temperature inside the greenhouse rose very high on hot, 
sunny days — a daily maximum of over 100° F. being the rule 
rather than the exception. 
During the preliminary experiment, in 1908, no record was 
kept of the temperature, humidity, or rate of evaporation in the 
greenhouse. During the latter half of the experiment of the fol- 
lowing year a record was kept of the evaporation from a free 
water surface, using two cylindrical jars, one of glass 4 inches in 
diameter and the other of white stoneware 6 inches in diameter. 
These were placed level with the tops of the cylinders, being sup- 
ported on a table covered with white paper. They were filled to 
a mark one inch from the top and at the end of each week water 
was added to raise the water to this mark. The evaporation 
record of that year is important in that it constitutes the only 
data recorded which indicate the relation of the general condi- 
tions in the greenhouse during the experiment of 1909 to those of 
the following two years. In the experiment of 1910 the evapora- 
tion from a free water surface was determined from March 12 on, 
using four glass jars like the glass jar of the preceding year and 
similarly supported. They were placed at the four corners of the 
framework enclosing the metal cylinders. There were no im- 
portant differences between the different jars in the amount of 
evaporation from week to week. In the 1911 experiments two 
glass jars similar to those of the preceding year were used but 
they were sunken in the soil surrounding the cylinders so that 
the mark on each was level with the surface of the soil as shown 
in the case of the one in figure 21. It will be seen from Table 2 
that the recorded rate of evaporation in 1911 was two or three 
times as great as in the preceding two years. This was due in 
part to the increased air movement in the greenhouse on account 
of better ventilation. The rate of evaporation recorded in this 
year appears remarkably high. 1 A record 2 of the rate of evapora- 
tion in the near-by open air was kept by the IT. S. Weather 
Bureau, but unfortunately for only part of the period, the evapo- 
rating pan being less than 200 yards from the greenhouse. The 
data from this record are included in Table 2. 
1 Similar high rates have been recorded in Australia where an evapora 
tion of from 140 to 160 inches in 12 months was recorded, using small 
evaporating cylinders. Report of Meteorological Observations for Western 
Australia in 1907, p. 7 and p. 110. 
2 Loveland, G. A., and Perin, S. W. Evaporation from a Free-Water Sur- 
face at Lincoln, Nebraska. Twenty-fifth Annual Report of the Nebraska 
Experiment Station, 1912, p. 193. 
