PDF - Wallace Online

i CLIMATE AND ASPECTS OF THE EQUATORIAL ZONE 226tion ;in the other case it radiates away into space, and is lost,more rapidly than it is being absorbed. In both cases anequilibrium will be arrived at, but in the one case the resultingmean temperature will be much higher than in the other.Thus we can understand the burning effects of the sun's raysin the tropics, since it results from the inability of the skinto part with the heat, either by radiation, evaporation, orabsorption, as fast as it is received, and thus a temperature isquickly reached which disorganises the delicate structures ofthe epidermis.Influence of Winds on the Temperature of the EquatorThe distance from the northern to the southern tropicsbeing considerably more than three thousand miles, and thearea of the intertropical zone more than one-third the wholearea of the globe, it becomes hardly possible for any currentsof air to reach the equatorial belt without being previouslywarmed by contact with the earth or ocean, or by mixturewith the heated surface-air which is found in all intertropicaland sub-tropical lands. This warming of the air is renderedmore certain and more effective by the circumstance that allcurrents of air coming from the north or south have theirdirection changed owing to the increasing rapidity of theearth's rotational velocity, so that they reach the equator aseasterly winds, and thus pass obliquely over a great extent ofthe heated surface of the globe. The causes that produce thewesterly monsoons act in a similar manner, so that on theequator direct north or south winds, except as local land andsea-breezes, are almost unknown. The Batavia observationsshow that for ten months in the year the average directionof the wind varies only between 5 and 30 from due east orwest, and these are also the strongest winds. In the twomonths March and October when the winds are northerly,they are very light, and are probably in great part localsea-breezes, which, from the position of Batavia, mustcome from the north over about two thousand miles of warmland and sea. As a rule, therefore, every current of air ator near the equator has passed obliquely over an immenseextent of tropical surface and is thus necessarily a warmwind.Q