578 STATE BOARD OF AGRICULTURE. 



The above tables (30-41) with their respective charts, show the fol- 

 lowing main facts: (1) the daily temperature of all the soils at all 

 three depths fluctuated throughout the year, but in different degree 

 during the different months. The greatest monthly amplitude occurred 

 in June and was followed in order by May, July, August, April, Sep- 

 tember, October, November, December, January, March and February; 

 (2) sand showed the greatest ami)litude for the G and 12 inch depths 

 and was followed in order by gravel, clay, loam, and peat. The fluctua- 

 tion at the 18 inch depth was about the same for all the diffei-ent soils 

 with a slight difference in favor of the sand and gravel. The amplitude 

 of the 6 inch depth was the greatest in all soils and was followed in 

 order by the 12 and 18 inch depths. The variation between the 6 and 

 12 inch and the 6 and IS inch depths were very much greater in the 

 lighter soils than in the heavier soils. 



The small soil temperature fluctuation in the winter is very interest- 

 ing and needs special attention. Theoretically si)eaking we should ex- 

 pect a greater fluctuation in the winter than in the summer, with the 

 same variation in air temperature, because the si)ccific heat of the soils 

 in summer is close to 0.5, while in the winter it is half this value, 

 because the specific heat of ice is about half of that of water. This 

 smaller amplitude in the winter may be attributed to the following 

 chief causes: (1) in the winter the soil is heated only by conduction 

 while in the summer it is heated by conduction and also by absorption, 

 hence, the temperature is raised to a higher degree in the latter case, 

 and the gradient is higher; (2) the latent heat of ice plays an import- 

 ant part in keeping the magnitude of fluctuations low; and (3) when 

 the soil is covered with a thick layer of snow, its temperature is kept 

 quite steady and varies but slightly. 



SEASONAL AND YEARLY AVERAGE AND RANGE OP TEMPERATURE. 



On the preceding pages the temperature of the different types of soil 

 has been considered from the standpoint of daily and monthly averages 

 and ranges. It will now be well to present the same data in these 

 forms, bv season and vear, and thus see what the relations are in these 

 longer periods of time. The data are shown herewith : 



