472 THE TROPICAL WORLD. 



and exists mainly in the waters which sweep around the icebound shores. In the 

 Tropical World, of which we are now to speak, the intense rays of the vertical sun 

 call into being an exuberance of animal and vegetable life unknown to other regions. 



Here, in the outset, it is well to define, as nearly as may be done, the geographical 

 limits of the zones or belts of the earth, and especially of that with which we are now 

 most immediately concerned, which we designate as Tropical, as distinguished from the 

 Temperate Zones which lie upon each side of it, and the Polar, which lie on each side 

 still farther beyond, to the north and the south. 



As used by geographers, the Tropical Zone includes that belt of the earth's sur- 

 face extending 23i-o on each side of the equator, bounded on the north by an 

 imaginary line called the Tropic of Cancer, on the south by the Tropic of Capricorn. 

 These mark the points from which the sun appears to make a turn (Greek r^urj;, 

 trope, whence the name) toward the equator, from its utmost declination toward the 

 north and south. It is only between these points that the sun ever appears directly 

 overhead ; north of these it is always seen to the south, and south of them to the 

 north. This forms the Torrid Zone, or belt of extreme heat. But as the prevailing 

 forms of vegetable and animal life which characterize this zone extend considerably 

 further in both directions, we shall use the word Tropical in a somewhat wider sense, 

 and by tlie Tropical World shall designate all that part of the earth's surface between 

 the equator and the thirtieth parallel of latitude on each side, forming a single belt of 

 60° in width. Perhaps the best single characteristic of this zone is, that within it 

 alone the various species of the palm tree have their home. 



The Polar World, as we have used the phrase, designates the zones at the north and 

 south where the cold is so excessive as to prevent the growth of grains and esculent 

 plants suited to the use of man. The parallels of 60°, north and south, are the 

 approximate boundaries of these zones, although the actual limit is sometimes above 

 and sometimes below this. Thus in Europe and on the western coast of America, the 

 polar limit is as high as 65°; while on the eastern coast of America, as in Labrador, 

 it sinks as low as 50°. 



The Temperate Zones comprise the surface of the globe between the parallels of 30° 

 and 60° north and south latitude. 



These great climatic divisions shade into each other ; but it may be said in general 

 terms that each occupies a space of 60° of latitude, as follows : 



The Polar Zones, 90° to 60° north and south. 



The Temperate Zones, 60° to 30° north and south. 



The Tropical Zones from the equator to 30° north and south. 



The whole of P^urope, more than nine-tenths of Asia, a narrow strip of Africa, and 

 all of North America except Mexico, and a small portion of Texas and Florida, lie 

 north of the tropical limit. Patagonia, the bare southern extremity of Africa, half of 

 Australia, and the almost unknown land around the southern pole, with a few islands, 

 are all the land south of the tropics. The Tropical World comprises Mexico, Central 

 America, nearly the whole of South America and Africa, and nearly all the great 

 islands of the globe, including the West India Islands, Polynesia, the islands of the 

 Indian Ocean, and half of Australia. 



The ocean covers three-fourths of the surface of the globe. Of the land, three- 

 quarters is in the northern hemisphere, and one-quarter in the southern. The Arctic 



