GENEEAL OBSEEVATIONS ON THE WINDS. 99 



Easterly character altogether. And not only this, but the Northern and 

 Southern currents, here meeting and opposing, will mutually destroy each 

 other, leaving only the actions of local causes, which may He in one region 

 in one way, and in another in a different one. 



The result of this, then, is the production of two great Tropical belts of 

 North-Easterly and South-Easterly winds, while the winds in the Equatorial 

 belt which separates them should be free from any steady prevalence of an 

 Easterly character, and should also be comparatively calm. All these 

 consequences are agreeable to observed fact, and constitute the system of 

 the regular Trade Winds. 



(5.) The constant friction of the earth upon the air near the Equator, it 

 may be objected, would, by degrees, destroy the rotation of the whole mass ; 

 but it is compensated in this manner : the heated Equatorial air, rising and 

 flowing off toward the Poles, carries with it a rotatory velocity much greater 

 than that of the surface over which it passes in its Northward and South- 

 ward progress. Hence it will gain more and more on the surface of the 

 earth, and assume more and more a Westerly vqIoXiyq direction; and when, 

 at length, it necessarily returns to the surface in its circulation, which it 

 must do, more or less, in all its course, it will act on it by its friction as a 

 powerful S.W. wind in the Northern Hemisphere, and a N.W. wind in the 

 Southern, and thus restore the equilibrium. Some consider that this is 

 the origin of the S.W. and Westerly gales so prevalent in our latitudes, 

 and of the almost universal Westerly winds in the Northern part of the 

 North Atlantic Ocean.* 



(6.) Now it will be seen tha fc by this theory the Trade Winds meet near 

 the Equator, leaving a belt of Calms of varying breadth between them. 

 According to Commander Maary, the winds here being neutrahzed rise up, 

 and cross each other ; the wind brought by the S.E. Trade passing over 

 the N.E. Trade as a S.W. upper current ; and, having passed the Cahiis 

 or Variables of the Tropic of Cancer, it appears as the ordinary Anti-Trade 

 or S.W. prevalent wind. The chief physical fact upon which this theory 

 is based is the red dust, found frequently to fall on vessels near the Cape 



* Sir John Herschel gives the following note in his work upon the Origin of Storms, 

 which, as it is most feasible, we give here ; it must be observed that it was written before 

 the views and observations of Raid, Rediield, and others, had been published. We shall 

 advert to it hereafter. 



" It seems worth enquiry, whether Hurricanes in tropical climates may not arise from 

 portions of the upper currents prematurely diverted downwards before their relative 

 velocity has been sufficiently reduced by friction on, and gradually mixing with, the 

 lower strata ; and so dashing upon the earth with that tremendous velocity, which gives 

 them their destructive character, and of which hardly any rational account has yet been 

 given. Their course, generally speaking, is in opposition to the regular Trade Wind, as 

 it ought to be, in conformity with this idea. — {Young's Lectures, vol. i., page 704.) But it 

 by no means follows that this must always be the case. In general, a rapid transfer, 

 either way in latitude, of any mass of air which local or temporary causes might carry 

 ubove the immediate reach of the friction of the earth's s^irface, would give a fearful exagger- 

 ation to its velocity. Wherever such a mass should strike the earth, a Hurricane might 

 arise ; and should two such masses encounter in mid-air, a Tornado of any degree of 

 intensity on record might easily result from their combination." — Astronomy, page 132. 

 The more recant views of Sir John Herschel and others will be found in their place 

 liereafcyr. 



