The international geography . eans ofinstruments. Temperature.—So far as our knowledge goes, the interior ofthe Earth, although undoubtedly at a high temperature, contributes a negligible quantity of heat to the atmo-sphere, and the heat which raises thetemperature of the air above that of in-terplanetary space is wholly derived fromthe Sun. The foundations of meteorologyand climatology are therefore to be soughtin physical astronomy. Distribution of Solar Heat.—Thesimplest case to consider is the ^ bution of temperature to be expected onthe surface of a globe of the same sizeand shap
The international geography . eans ofinstruments. Temperature.—So far as our knowledge goes, the interior ofthe Earth, although undoubtedly at a high temperature, contributes a negligible quantity of heat to the atmo-sphere, and the heat which raises thetemperature of the air above that of in-terplanetary space is wholly derived fromthe Sun. The foundations of meteorologyand climatology are therefore to be soughtin physical astronomy. Distribution of Solar Heat.—Thesimplest case to consider is the ^ bution of temperature to be expected onthe surface of a globe of the same sizeand shape as the Earth, rotating underthe same astronomical conditions, butFig. ^i.—lndiuation and healing presenting to the Sun a uniform land power of Solar Ravs. ^ .,, , , i • surface without any atmospheric en-velope. The amount and intensity of the solar radiations falling upon agiven area depend upon the angle at which they are received, as appearsfrom the diagram (Fig. 41). Let S represent a bundle of parallel rays, 72. Climate 73 6 then Aa, Ab, Ac, Ad each receive the same total number, but Aa(perpendicular to the rays) is demonstrably shorter than Ab, Ab thanAc, Ac than Ad, and so on; that is, the greater the altitude of theSun the greater is the intensity of the radiation received on a unit ofsurface. Speaking generally, the altitude of the Sun is greatest at theequator, and diminishes as the latitude increases, so that if the Sunremained always vertically over the equator (its position at the equinoxes)the amount of light and heat received at any place on the Earths surfacewould be a simple function of the latitude, the length of day and nightbeing everywhere equal. But the Sun travels over a belt extending to23^° on each side of the equator, so this simple relation is only approxi-mately true for a few days in the year about the time of the the tropics the altitude of the Sun varies comparatively little, andbeyond them it changes more and more acco
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectgeography, bookyear19
