VARIETIES OF TROPICAL CLIMATE 5 



the sea. Thanks to this salutary interchange, the Gulf Stream, 

 issuing from the Mexican Sea, and thence flowing to the north 

 and east, conveys a portion of its original warmth as far as the 

 west coast of Spitzbergen and Nowaja Semlja; while in the 

 southern hemisphere we see the Peruvian stream impart the 

 refrigerating influence of the antarctic waters to the eastern 

 coast of South America. 



The geographical distribution of the land within the tropics 

 likewise tends to counterbalance or to mitigate the excessive 

 heat of a vertical sun ; for a glance over the map shows us at 

 once that it is mostly either insular or extending its narrow 

 length between two oceans, thus multiplying the surface over 

 which the sea is able to exert its influence. Thus the Indian 

 Archipelago, the peninsula of Malacca, the Antilles, and Central 

 America, are all undoubtedly indebted to the waters which bathe 

 their coasts for a more temperate climate than that which they 

 would have had if grouped together in one vast continent. 



The temperature of a country proportionally decreases with 

 its elevation ; and thus the high situation of many tropical 

 lands moderates the effects of equatorial heat, and endows them 

 with a climate similar to that of the temperate, or even of the 

 cold regions of the globe. The Andes and the Himalaya, the 

 most stupendous mountain-chains of the world, raise their snow- 

 clad summits either within the tropics or immediately beyond 

 their verge, and must be considered as colossal refrigerators, 

 ordained by Providence to counteract the effects of the vertical 

 sunbeams over a vast extent of land. In Western Tropical 

 America, in Asia, and in Africa, we find immense countries 

 risinPT like terraces thousands of feet above the level of the 

 ocean, and reminding the European traveller of his distant 

 northern home by their productions and their cooler tempera- 

 ture. Thus, by means of a few simple physical and geological 

 causes acting and reacting upon each other on a magnificent 

 scale. Nature has bestowed a wonderful variety of climate upon 

 the tropical regions, producing a no less wonderful diversity of 

 plants and animals. 



But warmth alone is not sufficient to call forth a luxuriant 

 vegetation : it can only exert its powers when combined with 

 a sufficient degree of moisture; and it chiefly depends upon 

 the presence or absence of water whether a tropical country 



B 3 



