EXPERIMENT STATION BULLETINS. 733 



and gravelly types of soil contain a low percentage of water and conse- 

 quently a small total heat capacity, they would cool at a greater rate 

 and have a lower average temperature in the fall than such classes of 

 soil as the loam, clay and peat which contain a relatively high water con- 

 tent and hence a large heat capacity. 



This even rate of cooling and equal average temperature in the fall 

 and winter months of the different types of soil both when their surface 

 is covered with the thin layer of sand and when it remains uncovered in- 

 dicate that there is no one intrinsic factor during this period which is 

 sufficiently powerful to predominate and cause a variation in the tempera- 

 ture of these various soils. 



The main and most important facts revealed l\y the daily and monthly 

 march of the temperature of the different types of soil during the sec- 

 ond year when they were not covered with a layer of sand may be sum- 

 marized then as follows: (1) All these diverse types of soil froze at 

 about the same time at the various corresponding depths, with peat at 

 a slightly lower rate and had practically the same magnitude of tem- 

 perature throuahout the winter; (2) During a period of cold weather 

 they all reached an equal minimum of temperature and at the same day 

 at all three depths; (3) In the spring the sand and gravel thawed first, 

 followed by loam and clay about one or two days later and peat several 

 days later, down to the 18-inch depth; (4) Immediately upon complete 

 thawing the average temperature of the sand and gravel rose a few de- 

 grees above that of the loam and clay and several of that of peat. In 

 about three or four days, however, the temperature of the clay and loam 

 rose to about the same magnitude as that of the sand and gravel, but 

 that of the peat required considerably longer time to approach the same 

 point; (5) The temperature of all the soils at all three depths continued 

 to rise, after complete thawing, and almost attained the same magni- 

 tude but it did not become equal until in the fall. Up to this time it 

 varied, being highest in the sand and gravel, followed in order by loam, 

 clay and peat, respectively; (6) With the commencement of the fall the 

 temperature of all the soils began to be equal and continued to be about 

 the same throughout the fall months until the third year began in 

 December, 



It will now be seen how the foregoing results compare with those of 

 the following or third year. 



With the commencement of the third year. December 1, 1913 to No- 

 vember 30, 1914, all the different types of soil were again covered with 

 a thin layer of sand as in the first year, December 1, 1911 to November 

 30, 1912. The daily and monthly average temperature of the third year 

 are contained in Tables 13 to 24 inclusive. 



An examination of these tables reveals (1) that all the different types 

 of soil at all three depths did not freeze during the winter of the third 

 year. Toward the last week of December the 6-inch depth of the various 

 soils approached the freezing point but their temperature rose to about 

 33°F and prevailed at this point throughout the winter until in the 

 spring when it began to rise. The temperature of the 12-inch depth re- 

 mained throughout the entire winter at about 35°F and that of the 18- 

 inch depth at about 36°F. The magnitude of the daily and monthly 

 average temperature was remarkably close in all types at the respective 

 depths. 



