Page:Physical Geography of the Sea and its Meteorology.djvu/189

 Rh over countries abounding in rivers, which 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 abounding 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 may be, 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 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 theory of the crossings re-stated, and the facts reconciled by 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, 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