"310 OUTLINES OF NATURAL PHILOSOPHY. 



419. The Trade Wind itself is subject to cer- 

 tain irregularities. As the sun advances into the 

 Northern Hemisphere, the Trade Wind becomes 

 irregular ; and about the middle of April, in all 

 the tract between Africa and the peninsula of In- 

 dia, and much farther to the east, it changes from 

 north-east to south-west, and continues to blow in 

 that direction, till the sun returns to the Southern 

 Hemisphere. ( 



The cause of this change is difficult to be assigned. 

 It seems probable, that by the sun's entry into the 

 Northern Hemisphere, he communicates great heat 

 to the sandy deserts of Africa, which lie to the west 

 or south-west of the seas just mentioned. The great 

 heat acquired by the sand of those deserts, produces 

 a rarefaction in the columns of air incumbent on 

 them, and consequently a tendency, in the columns 

 that are near them, and more moderately heated, to 

 flow in and displace the heated air. The air of the 

 Atlantic is most likely to do this, and in passing over 

 Nigritia, &c., to acquire a velocity that carries it on 

 eastward through the Indian Ocean. 



Perhaps the direction of the eastern coast of Africa 

 has a share in producing this effect. The advance 

 of the sun into the Northern Hemisphere, would 

 naturally give the Trade Wind an inclination to the 

 north, when, meeting obliquely with the coast of 

 Africa, and the elevated tracts in the interior, it is 

 inrned yet more to the north. Here, again, recei- 

 2 ving 



