28 DEW FOGS. 



DEW. 



Dew arises from the watery vapours which 

 ascend in the daytime from the earth, and, being 

 condensed by the cold at night, fall down again. 

 When, therefore, the night is very warm, there 

 falls little or no dew. When it is so cold that 

 the dew is frozen, it is then called hoar-frost ; 

 and the trees and grass appear as white as if they 

 were powdered. The reason is this : when trees 

 and other bodies are extremely cold, the vapours 

 falling upon them are changed into particles of 

 ice. In very severe cold, even the vapours issuing 

 from our mouths are frozen, and fasten themselves 

 in that state to the hair, as the dew does to the 

 grass. 



FOGS. 



Fogs, or mists, consist of watery particles, 

 which are raised into the air, where, not being 

 completely dissolved, they form a vapour, which 

 extends itself in the lower part of the atmo- 

 sphere, and is so thick that objects cannot be seen 

 through it. 



Fogs are more frequent in low, wet, and marshy 

 situations, near rivers and ponds, than in those 

 parts of a country which are high and dry. Fogs 

 are much more common in cold seasons and in 

 cold climates than in such as are warm ; because, 

 in the former, the watery particles, being con- 

 densed almost as soon as they proceed from the sur- 



