158 MAINE STATE COLLEGE 



Comparing results, open field and forest, we have excess of 

 moisture in forest above that in open field expressed in percent- 

 ages. 



7 A. M. i P. M. 7 P. M. Mean 



5 15 10 10 



It thus appears from observations covering the period of 

 growth of three years, that the excess of moisture in forest 

 above that of open field in the morning, amounts to but 5 per 

 cent., while in the middle of the day it rises to 15 per cent., 

 and at night-fall drops down to 10 per cent., and that the 

 mean excess for the day is 10 per cent. In a very dense forest 

 the percentage of excess would undoubtedly rise much 

 higher. The presence of patches of forest in any region 

 exerts a marked influence on the hygroscopic conditions of 

 the atmosphere, and this condition, in turn, is an important 

 factor in the growth of vegetation. 



Soil Temperatures. 



In this investigation a knowledge of the temperature of the soil 

 at different depths, during the growing season, is sought, and 

 ultimately the law which represents the rate of change of tempera- 

 ture at different depths. 



The periods covered by the experiment are from May 1 to Nov. 

 1, 1689, from April 1 to Nov. 1, 1890, and from April 1 to Nov. 1. 

 1891, with thermometers placed in the soil to the depths of 1, 3, 

 6, 9, 12, 2i and 3>3 inches. 



The thermometers have been allowed to remain in place during 

 the winters intervening between the periods of observation. 



Their location is in the open field, near hygrometer No 2, in the 

 tract of land assigned to the Station for experimental purposes 

 and devoted to farm experiments. The character of the soil is 

 regarded, therefore, as representative of that on which the field 

 experiments by the Station are carried on. 



A summary of results for the three seasons by monthly aver- 

 ages is given in the annexed tables. 



