160 MAINK STATR COLLEGE 



that the rate has bcuni clearly viliuted since 1889 by the record of 

 the uiue inch thennonieter. 



The anomalous action of this instrument is accounted for by 

 the fact, that at the end of the year 1889, the nine inch thermom- 

 eter first used was broken and a new one was substituted. The 

 contact of the latter with the soil was not the same as that of the 

 former, nor has it been the same as that of the other instruments 

 which have not been disturbed in the four years. 



This accident, although vitiating the results of the present 

 investigation, is not without its value, since it clearly indicates 

 the need of maintaining uniform conditions in carrying on a work 

 of the nature and delicacy of that for which soil thermometers 

 are employed. 



Comparing soil temperatures with air temperatures during the 

 four seasons, the following mean results appear : At the depth 

 of 1 inch, the temperature of the soil was lower than at that of 

 the air by 2°. 32 ; at the depth of 3 inches, by 2°. 12 ; 6 inches, by 

 8°.22; 9 inches, by 3°.94 ; 12 inches, by 4M2 ; 24 inches, by 

 5°.86, and at the depth of 36 inches, by 7M6. 



Terrestrial Radiation. 



The heat radiated from the surface of the earth during the 

 night reduces its temperature several degrees below that of the 

 surrounding atmosphere. The amount of this radiation or the 

 consequent reduction of temperature is approximately shown by 

 comparing the readings of a terrestrial radiation thermometer 

 with those of a minimum thermometer. In obtaining data for 

 the comparison given below, the minimum thermometer was four 

 feet above the ground and the terrestrial radiation thermometer 

 was within six inches of its surface. The results are based on 

 monthly averages from May to October inclusive, 1889, from 

 April to October inclusive, 1890, 1891 and 1892. 



Table Showing Loss of Heat by Terrestrial Radiation. 



1889. 



May. Juue. July. Aug. Sept. Oct. Mean. 



o o o o o o o 



Mean of niininium temperatures 4G.63 53.25 55.08 53.65 49.07 33.91 48.50 



Mean of Temp, from Ter. Bad. Tber.. 38.48 49.20 50.59 47.60 44.60 28.48 43.17 



Loss of heat by radiation 8.15 4.05 4.49 



