THEORY OF WINDS. 325 



westerly winds predominate, and north-easterly 

 winds during winter, especially if the winter be 

 excessively rigorous. The same thing is true of 

 India, China, and Arabia. They are heated 

 during summer, and the atmosphere over them is 

 rarefied, which causes the air to flow in upon 

 them from the tropical seas, when it is deflected 

 to the east, by passing from latitudes that move 

 rapidly, to those which move more slowly. This 

 is what seamen term the south-west monsoon. 



When the sun is south of the equator, the air 

 moves from the northern land, which is cooled 

 down, towards the equator, that has a swifter 

 motion, thus causing the ntirth-east monsoon, 

 which corresponds with the north-east wind of 

 the North American cold season. It was sup- 

 posed by Volney, that the prevailing south-west 

 wind of the Mississippi valley was a recoil of the 

 tropical trade wind, deflected by the Andes of 

 Mexico ; but the fact which he states, of its 

 crossing the Alleghany Mountains, and advancing 

 north-eastward, as far as Montreal and Quebec, 

 is sufficient to prove, that it must be owing to a 

 cause far more extensive and general in its ope- 

 ration than mountain ranges. 



During summer in North America, the land 

 is greatly heated, and the air presses from the 

 Atlantic ocean, especially during the day, caus- 

 ing a sea breeze ; when from the south, it is 

 changed into a south-west wind, by passing from 



