80 THE PHYSICAL GEOGRAPHY OF THE SEA. 



143. And as for the general system of atmospherical circula- 

 tion which I have been so long endeavoring to describe, the Bible 

 tells it all in a single sentence : " The wind goeth toward the 

 south, and turneth about unto the north ; it whirleth about con- 

 tinually, and the wind returneth again according to his circuits." 

 — EccL, i., 6. 



144. Of course, as the surface winds H and D (Plate I.) ap- 

 proach the poles, there must be a sloughing off, if I may be allow- 

 ed the expression, of air from the surface winds, in consequence 

 of their approaching the poles. For as they near the poles, the 

 parallels become smaller and smaller, and the surface current must 

 either extend much higher up, and blow with greater rapidity as 

 it approaches the poles, or else a part of it must be sloughed off 

 above, and so turn back before reaching the calms about the poles. 

 The latter is probably the case. 



145. Our investigations show that the southeast trade-wind re- 

 gion is much larger than the northeast (I speak now of its ex- 

 tent over the Atlantic Ocean only) ; that the southeast trades are 

 the fresher, and that they often push themselves up to 10° or 15^ 

 of north latitude ; whereas the northeast trade-wind seldom gets 

 south of the equator. 



146. The peculiar clouds of the trade- winds are formed between 

 the upper and lower currents of air. They are probably formed 

 of vapor condensed from the upper current, and evaporated as it 

 descends by tlie lower and dry current from the poles. It is the 

 same phenomenon up there which is so often observed here below ; 

 when a cool and dry current of air meets a warm and wet one, an 

 evolution of vapor or fog ensues. 



147. We now see the general course of the "wind in his cir- 

 cuits," as we see the general course of the water in a river. There 

 are many abrading surfaces, irregularities, &c., which produce a 

 thousand eddies in the main stream ; yet, nevertheless, the gen- 

 eral direction of the whole is not disturbed nor affected by those 

 counter currents ; so with the atmosphere and the variable winds 

 which we find here in this latitude. 



148. Have I not, therefore, very good grounds for the opinion 

 (§ 118) th.at the "wind in his circuits," though apparently to us 



