90 THE EEASON WHY. 



'Hath the rain a father? or who hath begotten the drops of dew?" 

 JOB xxxviii. 



366. Why are certain coasts liable to almost perpetual 

 fogs? 



Because of local or geographical agencies which contribute to theii 

 production. The coasts of California are almost constantly wrapped 

 in fog ; and, almost as constantly, the western coast of the American 

 continent, as far south as Peru. Newfoundland, Nova Scotia, and 

 Hudson's Bay, are all subject to dense and frequent fogs arising 

 from the condensation of vapour from the water flowing from the 

 hot Gulf- stream, coming in contact with the colder air. 



367. What are dry fogs ? 



Dry fogs are characterised by a dull opaque appearance of the 

 atmosphere. They are most common in certain parts of North 

 America, though they sometimes occur in Germany and in England. 

 They are generally referred to the electrical state of the atmosphere, 

 but the theory of them is still a matter of doubt. 



368. Wliat is a mist ? 



The term mist is generally applied to vapours that rise over 

 marshy places, or the surfaces of water, and. roll or move over the land. 



369. Wliat is the difference between a mist and a fog ? 

 Fogs, as they are known to us, generally arise over the land, and 



are usually mingled with the smoke of large towns. Mists generally 

 arise over water, or wet surfaces. 



370. Why do mists and fogs disappear at sunrise ? 

 Because the condensed vapours are again expanded and dis- 

 persed by the heat of the sun's rays. 



371. Why do fogs frequently rise in the morning and fall 

 again in the evening. 



Because, warmed by the sun's rays, they become more rarefied, 

 and fly away at an altitude where they appear to be altogether 

 dispelled ; but at night, when the earth cools by radiation, the 

 vapours near the earth again condense, and settle in the for m of 

 fa- 



372. Why do fogs sometimes rest v/pon a given locality for 

 several days together, and then disappear ? 



