FOG. 227 



the same, viz. COLD condensing the 

 vapour of the air, when it is near the 

 point of saturation. 



Q. Why does MIST and FOG VANISH at sun- 

 rise? 



A. Because the condensed particles 

 are again changed into invisible vapour, 

 by the heat of the sun. 



Q. Wliat is the difference between a MIST and 

 FOG? 



A. MIST is generally applied to 

 vapours condensed on marshes, rivers, and 

 lakes. 



FOG is generally applied to vapours 

 condensed on land, especially if those 

 vapours are laden with smoke. 



Q. What is the reason why condensed vapour 

 sometimes forms into CLOUDS, and sometimes into 

 FOG? 



A. If the surface of the EARTH be 

 hotter than the air, then the vapour 

 of the earth (being chilled by the cold 

 air) becomes FOG : but if the AIR be 

 hotter than the earth, the vapour rises 

 through the air, and becomes CLOUD. 



Q. If cold air produces FOG, why is it not 

 on a FROSTY MOJRNING ? 



