Читать книгу The Circle of Knowledge: A Classified, Simplified, Visualized Book of Answers - Various - Страница 149

In some parts of the Earth extensive tracts exist where rain is never known to fall, and if at all only at intervals, and then in small quantities. The rainless districts of the New World include the flat territories of northern Chili and Peru, some parts of Mexico, and some parts of California. In the Old World an extensive rainless band extends from the western shores of Africa to the central regions of Asia, including the Great Sahara Desert, Egypt, part of Arabia, and the Desert of Gobi. Countries so circumstanced, unless like Egypt rendered fertile by the irrigation of a great river, constitute the most arid and desolate regions of the earth.

The quantity of rain which falls in any region depends greatly on local causes, such as the variations of the surface, the prevailing winds or the proximity of the ocean. Rain is usually more copiously deposited in mountains and well-wooded islands than in any other description of surface.

In tropical regions the rains follow the sun, i.e., when the sun is north of the equator, the rains prevail in the northern tropic, and when south of that line in the southern tropic. This forms the rainy and dry seasons to which countries so situated are subject. This does not, however, apply to the whole intertropical regions, for in a zone extending from the fifth to the tenth parallels on each side of the equator there are two rainy and two dry seasons.

In the narrow belt called the variables, between the regions of the north and south trade-winds, rain is almost incessant, accompanied by thunder and lightning. In many parts of the intertropical regions during the rainy season the rain pours down in such torrents that a larger quantity falls in a few hours than in a whole month in temperate North America.