EASTING OF THE TEADE-WIKDS, ETC. 157 



in America. Between this calm belt and the head waters of these? 

 rivers there are no seas or other evaporatmg smfaces, neither are 

 they so situated with regard to the sea-coast that they may be, as 

 the shores of Eastern China and the Atlantic slopes of the United 

 States are, sii2:»phed mth vapoiu' by the winds from the sea-board. 

 When we consider the table (§ 353), the situation of the rainless 

 regions and diy coimtries with regard to the calm belt of Cancer, 

 we are compelled to admit that, come whence it may and by what 

 channels it may, there are flowing out of this calm belt two kinds 

 of au', one well charged with moisture, the other dry and thirsty 

 to a degree. 



355. The supposition that the diy air came fi-om the north and 

 The theory of the the moist from the south, and both as an upper cur- 

 Td tSS^eco'n. i^ent, is the only hypothesis that is consistent with 

 ciied by it. all the known facts of the case. The dry air gave 



up all its moistui'e when, as a surface wind, it played upon the 

 frozen summits of the northern hills ; the wet obtained its mois- 

 tm^e when, as the south-east trade-^rads, it swept across the bosom 

 of intertropical seas of the southern hemisphere. Eising up at the 

 equator, it did not leave all its moisture with the cloud-ring, but, 

 retainmg a part, conveyed it through the cloud region, above the 

 north-east trades, to this calm belt, where there was a descent and 

 a crossing. The fact that these dry places are all within or on 

 the equatorial side of this calm belt, while countries abounding 

 with rains and well watered with running streams are to be found 

 all along its polar side, is clearly indicative of a crossing. Uj^on 

 no other supposition can we account for the barremiess on one 

 side, the fertility on the other. The following are also links in 

 the chain of facts and cncumstances which give strength to the 

 supposition that the rains for the Lena and the Missomi are 

 brought across the calm belt of Cancer by those cmTents of air 

 which flow thence towards the pole as the prevailing comiter- 

 trades or south-westerly winds of the extra-tropical north. We 

 have akeady seen (§ 353) that, on the north side of this calm zone 

 of Cancer, the prevailing winds on the surface are from this zone 

 towards the pole, and (Plate I., § 215) that these Vv^nds retmn as 

 ABC through the upper regions from the pole ; that, arriving at 

 the calms of Cancer, this upper current, ABC, meets another 

 upper current, S E, from the equator, where they neutralize each 

 other, produce a calm, descend, and come out as smface ^rads, 

 D E, or the trade-winds ; and as T U, or the counter-trades. 



