2"A HISTORY OF 



prevail for three or four months. The iMterval between thesp 

 winds, that is to say, from the end of June to the beginning of 

 August, there is no fixed wind ; but the sea is usually tossed by 

 violent tempests, proceeding from the north. These winds are 

 always subject to their greatest variations, as they approach the 

 land ; so that on one side of the great peninsula of India, the 

 coasts are, for near half the year, harassed by violent hurri- 

 canes and northern tempests : while, on the opposite side, and 

 all along the coasts of Coromande), these dreadful tempests are 

 wholly unknown. At Java and Ceylon, a west wand begii.s to 

 reign in the month of September; but at fifteen degrees of 



tlip north-'.vest wind south of the line seems not to be altogether constant, 

 and may perhaps arise from nothing more than a compound mnvotneiit, or a 

 higher current of air. What then is the originof this half-yearly wind, which 

 in summer blows from south and south-west, over all tlie Indian ocean ? 

 The sagacity of physical geographers has long been exercised by this question. 

 We aive the explanation of which Halley laid the ground-work, and which 

 appears to us the most plausible. 



The monsoons always change some time after the equinoxes ; they con. 

 stantly blovv towards that hemisphere in which the sun is fouud. The action 

 of this luminary on the atmosphere, is, therefore, plainly one of their causes. 

 When its rays, reflected from the mountains of Thibet, scorching the plains 

 of Bengal, and the valleys of the kingdom of Siam, rarefy and dissipate the 

 atmosphere, the cold air becomes violently attracted from the regions about 

 the south pole. The sun's action is seconded by the marine current, which 

 proceeds from the south polar seas to those of India. This current must 

 bring with it a column of vapours, continually disengaging themselves from 

 its surface. The absence of a northern marine current mu^t farther be added; 

 we can even imagine, that the mountains of Thibet, and the whole central 

 platform of Asia, may arrest and preserve the cold air, which would other. 

 wise proceed from Siberia towards India. 



But why does not this polar wind prevail south of the equator also ? For 

 the same reason which renders the aquatic polar current inconsiderable there. 

 The general movement of the ocean being opposed by no obstacle, has too 

 much force to be modified by the polar current. A similar result bappen.s 

 ni the atm.osphere, at all times intimately connected with the ocean, which 

 feeds and modifies it. But on leaving New Holland between us and tbc 

 Pacific Ocean, the general movement of the Indian sea must evidently ' 

 more and more abandoned to its individual force, and that force must soon 

 be overcome by the polar current, which, after being long deflected or cou- 

 ceaied by the general movement of the ocean, now re- appears in all its 

 energy. The polar column of water now fills the atmosphere with cold 

 particles, which, by their gravity, determine the whole atmosplieric ma^s to 

 flow towards the equator, more strongly and more directly than it would 

 have flowed otherwise. It is possible, moreover, that higher currents may 

 exist in tlie atmospboro, and descen.! towards the earth at the lime wliea 

 the monsouDB comnK^tcee 



