248 THE POPULAR SCIENCE MONTHLY 



In a true tropical climate seasons, in our sense, do not exist. The 

 variations in temperature throughout the year are so slight that the 

 seasons are not classified according to temperature, but depend on 

 rainfall and the prevailing winds. The life of animals and of plants 

 in the tropics, and of man himself, is regulated very largely, in some 

 cases almost entirely, by rainfall. Although the tropical rainy season 

 is characteristically associated with a vertical sun (i. e., "summer"), 

 that season is not necessarily the hottest time in the year. In fact, the 

 temperature is usually somewhat lower under the clouds, and hence the 

 rainy season often goes by the name of " winter." 



Within the tropics the equatorial belt of calms and variable winds 

 — the " doldrums " of sailors — offers exceptionally favorable condi- 

 tions for abundant rainfall. The rainfall is so heavy that the surface 

 waters of the ocean are actually fresher than in the latitudes to the 

 north and south. The sky is prevailingly cloudy; the air, hot and 

 oppressive; heavy showers and thunderstorms are frequent. In the 

 latitudes of this belt are the dense tropical forests of the Amazon and 

 of equatorial Africa. Here drought and frost need not be feared. 

 The belt of calms and rains shifts north and south of the equator after 

 the sun. It is dreaded by seamen because sailing vessels are apt to be 

 delayed in crossing it, but delays of great length are infrequent nowa- 

 days, since a careful study of the prevailing winds over the ocean areas 

 has shown navigators at what points the belt of calms is narrowest, 

 and where the crossing may be the most successfully made. 



In striking contrast are the easterly trade winds, which blow 

 toward the equator from about latitude 30° north and south. Of 

 great regularity, embracing about one half of the earth's surface, the 

 trades have long been favorite sailing routes because of the steadiness 

 of their winds, the infrequency of their storms, the brightness of their 

 skies and the freshness of the air, all of which are in pleasing contrast 

 with the muggy, oppressive calms of the doldrums. All sailing routes 

 which pass through the trade wind belts in any ocean are controlled 

 by these winds. Steady winds like the trades certainly tempted the 

 early navigators to put to sea. The famous voyage of Columbus was 

 facilitated, if not made possible, by the northeast trade. The easy 

 outward voyages of the early Spanish adventurers and colonists took 

 them naturally to that portion of the Americas where they found even- 

 tempered climates in which they and their descendants could live com- 

 fortably. The monsoons of India have from the earliest days of trade 

 with the east been important agents in aiding commerce. 



The most desirable house sites in the tropics are very commonly on 

 the top of some elevation, exposed to the trades. The sea breeze, also, 

 is an important climatic feature on many tropical coasts. "With its 

 regular occurrence, and its cool, clean air, it serves to make many dis- 

 tricts habitable for white settlers, and has deservedly won the name of 



