272 



MAINE STATE COLLEGE 



In order that comparisons may be made between the soil tem- 

 peratures at different depths and the air temperature in the same 

 locality, the following table is given : 



Thermometer in the open air ; locality the same as that of soil 

 thermometers. 



7 A. M. 



7 p. M. 



Mean. 



May, 



52.95 



68.30 



59.47 



60.24 



June, 



63.36 



74.27 



68.07 



68.57 



July, 



65.12 



75.75 



70.86 



70.58 



August, 



59.97 



74.20 



66.81 



66.99 



September, 



54.39 



70.86 



61.55 



62.27 



October, 



37.41 



52.80 



44.05 



44.75 



Mean, 55.53 69.36 61.80 62.23 



Table Showing Changes of Temperature in the Soil for 



Increased Depths. 



Depth 



of 



Thermometer. 



Mean tempera- 

 ture for six 

 months. 



Difference in 

 mean tempera- 

 ture. 



Changes in tem- 

 perature for one 

 inch. 



1 inch 



o 

 60.50 

 60.77 

 59.63 

 58.78 

 58.26 

 56.40 

 54.79 



o 



+0.27 

 —1.14 

 —0.85 

 —0.52 

 —1.86 

 —1.61 



o 



3 inches 



+0.13 

 —0.38 

 —0.28 

 —0.17 

 —0.15 

 —0.13 



6 inches 



9 inches 



12 inches 



24 inches 



36 inches 



An examination of the tables shows that the soil responds 

 readily to the daily heat of the sun to the depth of three inches, 

 less readily to the depth of six inches, in a moderate degree only 

 to the depth of nine inches, and very slightly below twelve inches. 

 To the depth of three inches the range between the morning and 

 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 7°. 18 ; at the depth of 3 inches, 6°.80 ; at the 

 depth 6 inches, 2°.80 ; at the depth of 9 inches, 1°.78, and below 

 12 inches, very slight. 



At the depth of 3 inches, the average tempei-ature of the soil 

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

 soil averaged about six degi'ees 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 



