FOG. 73 



that consequently no mist would be produced. But, 

 as before stated, it has been ascertained by experiment 

 that hot air at 100 will contain about two cubic inches, 

 and air at 50, about half a cubic inch of water. The 

 two would therefore contain two and a half cubic 

 inches. But air at 75 can hold but one cubic inch, 

 and consequently the two cubic yards would hold but 

 two cubic inches. The surplus half inch would con- 

 sequently take the form of visible moisture, called 

 cloud, fog, or mist, according to circumstances. It is 

 not to be understood, from what is above stated, that 

 half a cubic inch of water is always yielded by every 

 two cubic yards of air at 50 and 100 which come to- 

 gether ; if they are not totally saturated, the quantity 

 will be less. 



167. FOGS ON THE SEA COAST. The 



Why are fogs 



produced on sea is cooler than the land in summer, and 

 the sea coast? warmer m w i n t e r. As a consequence, the 

 air above the sea is cooler in summer and warmer in 

 winter, than that above the land. The admixture of 

 these bodies of air, which takes place along the coast, 

 produces fogs on the principle above stated. 



168. FOGS ON RTVERS. When land and 



Why do fogs 



form on riv- water have the same temperature, as may 

 be the case with small lakes and rivers, 

 the difference of radiation during a single night often 

 produces fogs. The land cools more rapidly than the 

 water. As a consequence, the air above the land is 

 cooler than that above the water. As the two bodies 



of air mingle, fog is produced, and is seen following 



4 



