390 



HYDROGRAPHY. 



places we see the Trade Winds checked by the temperature of other 

 winds, or lost in calms. In others, we find them merging in a perio- 

 dical Monsoon, obeying other influences, and flowing towards other 

 areas of higher temperature. In some cases, these are but temporary, 

 while in others, they are permanent ; — both the Northeast and South- 

 east Trade Winds of the Pacific are found to deviate towards the oppo- 

 site Tropic when it is warmed by the sun's rays. 



The Southeast Trade Wind of the Indian Ocean derives its great 

 supply from the heated air which rises above New Holland, is cooled, 

 and seeks in like manner the warmest area of the ocean to the west. 

 It passes over, also, a wide tract of ocean, before it descends and 

 becomes the surface Trade Wind. 



As the sun reaches high northern and southern declination, the air 

 is induced towards the great currents beyond their northern and 

 southern edges ; it is drawn in, as before mentioned in the explana- 

 tion of the progression of w T ind, from beyond the belt of calms ; but 

 the supply is but temporary, and very small, compared to the vast 

 volume that is required to keep up the circulation. 



The Southeast Trade Wind of the South Atlantic derives its supply 

 from the air which rises above and flows over the southern part of 

 Africa, and then descends at some distance from its west coast, and 

 pursues its route towards the Equator. 



In regarding the movements of winds, we invariably find, where 

 the greatest difference of temperature exists in close proximity, there 

 its greatest violence is experienced. Perhaps the best known 

 instances of this are found in countries where the mountains and 

 plains lie in juxtaposition. If we take, for instance, the winds in the 

 South of Europe, between the Alps and the Mediterranean Sea, these 

 are, according to Dove, " celebrated for their violence and severity." 

 We find that this extreme rapidity of the aerial current is due to the 

 great difference of temperature. At the same time, the wind is 

 known to blow very strong down the north side of the Alps, being 

 induced towards the higher temperature of the plains. In New 

 Holland, it not unfrequently occurs that the wind flows from the 

 northwest and west, from the interior, towards the east coast. This, 

 we suppose, to be owing to the cold and higher air being induced to 

 flow towards the heated area of the east coast. These winds are dry 

 and cold, the temperature often falling from 100° to 70° Fah. ; yet they 

 are felt to be almost suffocating to the feelings — and everything 



