158 THE PHYSICAL GEOGRAPHY OF THE SEA. 



the sea, and are replenished with vapor thence in sufficient quan- 

 tities to make rain of; whereas the winds which come out on the 

 polar side leave moisture enough as they come for such rivers as 

 the Obi, the Yenisei, the Lena, and the Amoor, in Asia; the Mis- 

 souri, the Sascatchawan, the Red River of the North, and others, 

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

 rivers there are no seas or other evaporating surfaces, 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, supplied with vapor by the winds from the sea-board. 

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

 regions and dry countries 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 air, one well charged with moisture, the other dry and thirsty 

 to a degree. 



355. The supposition that the dry air came from the north and 

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

 andlhffactrrecon' ^^^^j ^^ ^hc Only hypothcsis that is consistent with 

 cued by it. j^|| ^-^^ kuown facts of the case. The dry air gave 



up all its moisture when, as a surface wind, it played upon the 

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

 ure when, as the southeast trade-winds, it swept across the bosom 

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

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

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

 northeast 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. Upon 

 no other supposition can we account for the barrenness on one 

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

 the chain of flxcts and circumstances which give strength to the 

 supposition that the rains for the Lena and the Missouri are 

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

 which flow thence toward the pole as the prevailing counter- 

 trades or southwesterly winds of the extra-tropical north. We 

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



