THE EARTH. 



101 



In this manner is explained the constant 

 east wind that is found blowing round the 

 globe, near the equator. But it is also known, 

 that as we recede from the equator on either 

 side, we come into a trade-wind, that con- 

 tinually blows from the poles, from the north 

 on one side, or the south on the other, both 

 directing towards the equator. This also pro- 

 ceeds from a similar cause with the former; 

 for the air being more rarefied in those places 

 over which the sun more directly darts its 

 rays, the currents will come both from the 

 north and the south, to fill up the interme- 

 diate vacuity. 



These two motions, namely, the general 

 one from east to west, and the more parti- 

 cular one from both the poles, will account 

 for all the phaenomena of trade-winds; which, 

 if the whole surface of the globe were sea, 

 would undoubtedly be constant, and for ever 

 continue to blow in one direction. But there 

 are a thousand circumstances to break these 

 air-currents into smaller ones ; to drive them 

 back against their general course ; to raise 

 or depress them ; to condense them into 

 storms; or to whirl them in eddies. In con- 

 sequence of this, regard must be often had 

 to the nature of the soil, the position of the 

 high mountains, the course of the rivers, and 

 even to the luxuriance of vegetation. 

 : If a country, lying directly under the sun, be 

 very flat and sandy, and if the land be low and 

 extensive, the heats occasioned by the re- 

 flection of the sun-beams, produces a very 

 great rarefaction of the air. The deserts of 

 Africa, which are conformable to this descrip- 

 tion, are scarcely ever fanned by a breath 

 of wind by day; but the burning sun is con- 

 tinually seen blazing in intolerable splendour 

 above them. For this reason, all along the 

 coasts of Guinea, the wind is always per- 

 ceived blowing in upon land, in order to fill 

 up the vacuity caused by the sun's operation. 

 In those shores, therefore, the wind blows 

 in a contrary direction to that of its general 

 current; and is constantly found setting in 

 from the west. 



From the same cause it happens, that those 

 constant calms, attended with deluges of rain, 

 are found in the same part of the ocean. For 

 this tract being placed in the middle, be- 

 tween the westerly winds blowing on the 



coast of Guinea, and the easterly trade-winds 

 that move at some distance from shore, in a 

 contrary direction, the tendency of that part 

 of the air that lies between these two oppo- 

 site currents, is indifferent to either, and so 

 rests between both in torpid serenity ; and 

 the weight of the incumbent atmosphere, 

 being diminished by the continual contrary 

 winds blowing from hence, it is unable to 

 keep the vapours suspended that are copi- 

 ously borne thither ; so that they fall in con- 

 tinual ruins. 



But it is not to be supposed, that any 

 theory can account for all the phaenomena of 

 even those winds that are known to be most 

 regular. Instead of a complete system of the 

 trade-winds, we must rather be content with 

 an imperfect history. These," as was said, 

 being the result of a combination of effects, 

 assume as great a variety as the causes pro- 

 ducing them are various. 



Besides the great general wind above men- 

 tioned, in those parts of the Atlantic that lie 

 under the temperate zone, a north wind pre- 

 vails constantly during the months of Octo- 

 ber, November, December, and January. 

 These, therefore, are the most favourable 

 months for embarking for the East Indies, in 

 order to take the benefit of these winds, for 

 crossing the Line: and it has been often found, 

 by experience, that those who had set sail 

 five months before, were not in the least far- 

 ther advanced in their voyage, than those 

 who waited for the favourable wind. During 

 the winter of Nova Zembla, and the other 

 arctic countries, a north wind reigns almost 

 continually. In the Cape de Verde islands, 

 a south wind prevails during the month of 

 July. At the Cape of Good Hope, a north- 

 west wind blows during the month of Sep- 

 tember. There are also regular winds, pro- 

 duced by various causes, upon land. The 

 ancient Greeks were the first who observed 

 a constant breeze, produced by the melting 

 of the snows, in some high neighbouring 

 countries. This was perceived in Greece, 

 Thrace, Macedonia, and the jEgean sea. 

 The same kind of winds are now remarked 

 in the kingdom of Congo, and the most south- 

 ern parts of Africa. The flux and reflux of 



Buftbn, vol. ii. p. 230. 



