118 THE MONSOONS. SKCT. XV. 



been seen moving rapidly from west to east, at a very 

 great height above the trade-winds, which were sweep- 

 ing along the surface of the ocean in a contrary direc- 

 tion. Rains, clouds, and nearly all the other atmos- 

 pheric phenomena occur below the height of 18,000 

 feet, and generally much nearer to the surface of the 

 earth. They are owing to currents of air running upon 

 each other in horizontal strata, and differing in their 

 electric state, in temperature and moisture, as well as 

 in velocity and direction. 



The monsoons are steady currents six months in du- 

 ration, owing to diminished atmospheric pressure at each 

 tropic alternately from the heat of the sun, thereby pro- 

 ducing a regular alternation of north and south winds, 

 which combining their motion with that of the earth on 

 its axis become a north-east wind in the northern hem- 

 isphere and a south-west in the southern ; the former 

 blows from April to October and the latter from October 

 to April. The change from one to the other is at- 

 tended by violent rains, with storms of thunder and 

 lightning. From some peculiar conformation of the 

 land and water, these winds are confined to the Arabian 

 Gulf, the Indian Ocean, and the China Sea. 



When north and south winds blow alternately, the 

 wind at any place will veer in one uniform direction 

 through every point of the compass, provided the one 

 begins before the other has ceased. In the northern 

 hemisphere a north wind sets out with a smaller degree 

 of rotatory motion than the places have at which it suc- 

 cessively arrives, consequently it passes through all the 

 points of the compass from N. to N. E. and E. A cur- 

 rent from the south, on the contrary, sets out with a 

 greater rotatoiy velocity than the places have at which 

 it successively arrives, so by the rotation of the earth it 

 is deflected from S. to S. W. and W. Now if the vane 

 at any place should have veered from the N. through 

 N. E. to E. r and a south wind should spring up, it would 

 combine its motion with the former and cause the vane 

 to turn successively from the E. to S. E. and S. But 

 by the earth's rotation this south wind will veer to the 

 S. W. and W., and if a north wind should now arise, it 

 would combine its motion with that of the west and 



