THE ATMOSPHERE. 75 



question, have thrown so much hght upon it as to show that, if 

 ever it be answered by man, he must consult the science of astron- 

 omy. It has been recently all but proved, that the earth and sun, 

 with their splendid retinue of comets, satellites, and planets, are 

 all in motion around some point or centre of attraction inconceiv- 

 ably remote, and that that point is in the direction of the star Al- 

 cyon, one of the Pleiades ! Who but the astronomer, then, could 

 tell their " sweet influences ?" 



And as for the general system of atmospherical circulation 

 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 w^hirleth about continually, 

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

 i.,6. 



108. 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 al- 

 lowed 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 rapid- 

 ity as it approaches the poles, or else a part of it must be slough- 

 ed off above, and so turn back before reaching the poles. The 

 latter is probably the case. 



Our investigations show that the southeast trade-wind region is 

 much larger than the northeast. I speak now of its extent over 

 the Atlantic Ocean only ; that the southeast trades are the fresh- 

 er, 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. 



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 de- 

 scends by the 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. 



We now see the general course of the " wind in his circuits," 

 as we see the general course of the water in a river. There are 

 many abrading surfaces, irresrularitics, &c., which produce a thou- 



