130 OUTLINES OF FORESTRY. 



Moist air, moreover, is not only better able to 

 absorb the heat accompanying the direct rays of 

 the sun, but is especially able to absorb that kind 

 of heat which is thrown off from the heated earth. 

 Consequently, the air over a forest district absorbs 

 a much larger percentage of the heat flung off 

 from the heated earth than does the drier air over 

 a barren district. In this way, in winter, while the 

 ground is throwing off its heat, the moist air of 

 the forest tends to remain warmer than the air 

 over a dry, arid tract. 



Forests exert a marked influence on the climate 

 of a country, especially at that time of the year 

 when the crops are liable to suffer injury from 

 early frosts. 



The ease with which bare or poorly covered 

 ground throws off its heat permits such an area to 

 more readily reach the temperature of the danger- 

 point than would be the case if it were well 

 wooded. It must be remembered that the differ- 

 ence of a few degrees, or even of the fraction of a 

 degree, between the air over an uncovered district, 

 and the air over a covered district in the forest, 

 may make all the difference between the occurrence 

 of frost and its non-occurrence. It is, indeed, often 

 but the difference of a fraction of a degree, that 



