HOT-BEDS, COLD FRAMES, AND WEATHER. 73 



brought from the cold outside air into a warm room. The 

 value of dew to vegetation is manifested in such dry rain- 

 less seasons, as those of 1880 and 1881. This moisture 

 gathers where it is most needed, on low plants, the roots 

 of which do not penetrate the earth deeply, and on foliage 

 near the ground. The precipitation of moisture upon 

 tender vegetation, must diminish the cold wliich occa- 

 sioned it, and thus prevents the injury that might arise 

 from that cause. The partial prevention of cold on 

 an object near the ground, by the interposition of a 

 screen between it and the sky, is due to the reflection of 

 heat by the lower surface of the screen back to the object. 

 This compensates in part for the loss by radiation. 



The gardener avails himself of this, in protecting his 

 plants in cold and clear nights by the interposition of 

 screens, which are most effective when not in contact 

 with the vegetation to be protected. Clouds similarly 

 prevent injury from cold at night, by radiating heat to 

 the earth in return for what they intercept from the 

 earth. The lower the clouds the more effective they are. 

 Fog, or clouds of smoke, have the same effect as clouds 

 of vapor. Coast lands and islands, from their situation, 

 are more subject to a cloudy sky, to movement in the 

 air, and are therefore less exposed to cold by radiation; 

 but the chief reason why islands are more temperate than 

 continents and inland situations, is, that the water of the 

 ocean, a little below the surface, is uniformly in all lati- 

 tudes about 45. Florida as a long peninsula, with an 

 ocean east and west, and Bermuda, as evidenced by her 

 extremely early crops, although lying in the same lati- 

 tude as Savannah, enjoy these advantages in an eminent 

 degree, besides having the warm waters of the Gulf 

 Stream flowing near their coasts. The cooling of a 

 body exposed on a clear night, depends in part upon 

 the readiness with which it receives heat by conduction 

 from bodies warmer than itself in contact with it. 



