230 BADIATION. 



in consequence of which, more vapour is 

 condensed and frozen there. 



Q. Why -is the AIR (resting on the surface of 

 the EARTH) colder than that in the HIGHER regions ? 



A. Because the earth radiates more 

 heat than the leaves of lofty trees; and, 

 therefore, condenses and freezes the 

 vapour of the air more rapidly. 



Q. Why are EVERGREENS often FROST- 

 BITTEN, when lofty trees are NOT? 



A. Evergreens do not rise far above 

 the surface of the earth ; and (as the air 

 contiguous to the earth is much colder 

 than that in the higher regions) therefore, 

 the low evergreen is often frost-bitten, 

 when the lofty tree is uninjured. 



Q. Why are TOMB-STON E s covered with HOAR- 

 FROST, long after it has melted from every object 

 around ? 



A, White is a very lad absorbent of 

 solar heat; and, therefore, the white 

 tomb-stone remains too cold to thaw the 

 frost congealed upon its surface. 



Q. Why is there little or NO HOAR-FROST 

 under SHRUBS and shadowy TREES ? 



A. 1st Because the leafy shrubs 



