BASTING OP THE TRADE- WINDS, ETC. 163 



over countries abounding in rivers, whicL. countries are therefore 

 abundantly supplied with rains. Hence we infer (§ 350) that 

 those winds are rain winds. On the other hand, the winds that 

 flow out on the equatorial side blow either over deserts, rainless 

 regions, or dry countries. Hence we infer that these winds 

 are dry winds. These *' dry " winds traverse a country abound- 

 ing in springs and rivers in India, but it is the monsoons there 

 which bring the water for them. The winds which come out of 

 this calm belt on its equatorial side give out no moisture, except 

 as dew, until they reach the sea, and are replenished with vapour 

 thence in sufficient quantities 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 Missouri, 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 maybe, as the shores of Eastern 

 China and the Atlantic slopes of the United States are, supplied 

 with vapour by the winds from the sea-board. When we con- 

 sider 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 theory of the crossings re-stated, and the facts reconciled 

 hy it. — The supposition that the dry air came from the north and 

 the moist from the south, and both as an upper current, is the 

 only hypothesis that is consistent with all the known 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 moisture when, as the south-east 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, con- 

 veyed 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 



