126 THE PHYSICAL GEOGRAPHY OF THE SEA. 



and ascend, cross over and continue their course as an upper cur- 

 rent to the calms of Cancer, while the air that the northeast trade- 

 winds discharge into the equatorial calm belt continues to go south, 

 as an upper current bound for the calms of Capricorn. But what 

 should cause this wind to cross over ? Why should there not be 

 a general mingling in this calm belt of the air brought by the two 

 trade-winds, and why should not that which the southeast winds 

 convey there be left, after its ascent, to flow off either to the north 

 or to tlie south, as chance directs ? 



302. In the first place, it was at variance with my faith in the 

 grand design ; for I could not bring myself to believe that the op- 

 erations of such an important machine as the atmosphere should 

 be left to chance, Bven for a moment. Yet I knew of no agent 

 which should guide the wind across these calm belts, and lead it 

 out always on the side opposite to that on which it entered ; nev- 

 ertheless, certain circumstances seemed to indicate that such a 

 crossing does take place. 



303. Evidence in favor of it seemed to be afforded by this cir- 

 cumstance, viz., our researches enabled us to trace from the belt 

 of calms, near the tropic of Cancer, which extends entirely across 

 the seas, an efflux of air both to the north and to the south ; from 

 the south side of this belt the air flows in a never-ceasing breeze, 

 called the northeast trade-winds, toward the equator, (Plate I.) 



On the north side of it, the prevailing winds come from it also, 

 but they go toward the northeast. They are the well-known south- 

 westerly winds which prevail along the route from this country to 

 England, in the ratio of two to one. But why should we suppose 

 a crossing to take place here ? 



304. We suppose so, because these last-named winds are going 

 from a warmer to a colder climate, and therefore it may be infer- 

 red that nature exacts from them what we know she exacts from 

 the air under similar circumstances, but on a smaller scale, before 

 our eyes, viz., more precipitation than evaporation. 



305. But where, it may be asked, does the vapor which these 

 winds carry along, for the replenishing of the whole extra-tropical 

 regions of the north, come from ? They did not get it as they 

 came along in tlie upper regions, a counter-current to the north- 



