Читать книгу The Circle of Knowledge: A Classified, Simplified, Visualized Book of Answers - Various - Страница 124

The amount of heat produced by the sun upon the Earth’s surface, is greatest near the Equator, and diminishes gradually towards the Poles. Three general causes, each referable to the spherical form of the Earth, combine to produce the gradual diminution of temperature from the Equator to the Poles.

1. The angle at which the Sun’s rays strike the surface. In the Equatorial regions they are perpendicular to the surface of the sphere, and there produce their maximum effect; but, on account of the curved outline of the globe, they fall more and more obliquely with increasing latitude, and the intensity of action diminishes proportionately. At the Poles their effect is practically nothing.

2. The area on which a given amount of heating power is expended, is least at the Equator, consequently the resulting heat is greatest. The area covered increases, and the effect diminishes, with the increasing obliquity of the Sun’s rays in higher latitudes, which, as we have seen above, results from the spherical form of the Earth.

3. The absorption of heat by the atmosphere, as the Sun’s rays pass through it, is least where they fall perpendicularly—that is, in the Equatorial regions—and increases, with their increasing obliquity, towards the Poles.