66 NATURAL AND CIVIL 



beat will flow into the earth, and thus the heat 

 of the earth will be increased. When the heat 

 of the atmosphere is less than forty four degrees, 

 the heat will flow out of the earth into the at- 

 mosphere, and in this way the internal parts of 

 the earth will be losin.^ their heat, or becoming 

 colder. This is the case during the winter 

 months ; or rather, from the middle of October, 

 to the bei^innino: of Aoril. Hence the surface 

 of the earth -v^hen exposed to the atmosphere, 

 becomes frozen to a greater or less depth, ac- 

 cording to the degree and duration of the cold. 

 The snow tends very much to prevent this. 

 By covering over the surface of the ground a 

 considerable depth, the snow by its nature and 

 colour, pre\'ents the internal heat of the earth 

 fi'om flowing into the colder atmosphere, and 

 the atmosphere from coming into contact with 

 the earth. In this way Avhile the earth is cov- 

 cred w^ith a deep snow, its heat is preserved, 

 and the surface, in tlie coldest weather, is kept 

 warm. To ascertain to -what degree the heat 

 of the earth was aflected, by the quantity of 

 snow that lay upon it, on January 14, 1791 (an 

 extreme cold winter) I dug through the frozen 

 surface in a plain open field, where the snow- 

 had been driven away b}- the ^vind, and found 

 the ground was frozen to the depth of three 

 feet and five inches. In the woods, ^a here the 

 snow was three feet deep, I found on the same 

 day the heat of the earth, six inches below the 

 surface, was thirty nine degrees. The surface 

 of the earth had been frozen to this depth, be- 

 fore it was covered with sno^\'. The frost was 

 not only extracted, but the surface of the earth 



