164 MAINE STATE COLLEGE 



the midday observations has been as high as fifteen degrees. 

 The mean daily range at the depth of 1 inch during the period of 

 observations was 5°. 55 ; at the depth of three inches, 4°.77 ; at the 

 depth 6 inches, 2°. 00 ; at the depth of 9 inches, 1°.09, and below 

 12 inches very slight. 



At the depth of 3 inches, the average temperature of the soil 

 was somewhat higher than at the depth of 1 inch: The surface 

 soil averaged about five degrees warmer than the soil 36 inches 

 below the surface. 



The rate of reduction of temperature with depth below the layer 

 three inches from the surface is clearly shown in the foregoing 

 tables. 



It is interesting to notice how closely the changes in temperature 

 for one inch accord with one another, in the different years, at 

 corresponding depths. 



The apparent rate of reduction of temperature with depth is 

 vitiated, however, by the record of the 9-inch soil thermometer- 

 This anomalous record is explained by the fact that at the end of 

 the first season this thermometer was broken and a new one had 

 to be. substituted in its place. The contact of the latter with the 

 soil was not precisely the same as that of the former or of the 

 other instruments that had not been disturbed. Judging from the 

 tables, another year will be needed to restore uniformity of con- 

 dition among the several instruments. This accident, with the 

 resulting error introduced, well illustrates the delicacy of the 

 work carried on by means of the soil thermometers. 



Comparing soil temperatures with air temperatures during the 

 three seasons, the following mean results appear : At the 

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

 of the air by 2°. 16 ; at the depth of 3 inches, by 1°.89 ; 6 inches, 

 by 3°. 08 ; 9 inches, by 3°. 83 ; 12 inches, by 4°. 06 ; 24 inches, by 

 5°. 80, and at the depth of 36 inches, by 7°11. 



Terrestrial Radiation. 

 The heat radiated from the surface of the earth during the 

 night reduces its temperature several degrees below that of the 

 surrounding atmosphei'e. 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 



