THE WORLD'S WONDERS. 31 



world. Karified by the intense heat of a vertical sun, the air 

 within the tropics rises in perpendicular columns high above the 

 surface of the earth, and thence flows off toward the poles ; 

 while, to fill up the void, cold air currents come rushing in from 

 the Arctic and Antarctic regions ; but the rotation of the earth 

 gradually diverts the direction of these cold currents, and changes 

 them into trade-winds, which regularly blow over the greater 

 portion of the tropical ocean from east to west, and materially 

 contribute to the health and comfort of the navigator whom they 

 waft over the equatorial waters. The trade-wind is an air current 

 of even greater importance than the water current known as the 

 Gulf Stream. This wind covers no less than 56 of latitude 

 28 north and 28 south of the equator. In this large tract, 

 which comprises many of the most fertile countries on the globe, 

 the trade-wind blows during the whole year, either from the 

 north-east or from the south-east. The causes of this regularity 

 are now well understood, and are known to depend partly on the 

 displacement of air at the equator, and partly on the motion of 

 the earth ; for the cold air from the poles is constantly flowing 

 toward the equator and thus producing northerly winds in the 

 northern hemisphere, and southerly winds in the southern. 



The trade-wind, blowing on the eastern coast of South America, 

 and proceeding from the east, crosses the Atlantic Ocean, and 

 therefore reaches the land surcharged with the vapors accumu- 

 lated in its passage. The vapors, on touching the shore, are, at ? 

 periodical intervals, condensed into rain ; and as their progress 

 westward is checked by that gigantic mountain chain, the Andes, 

 which they are unable to pass, they pour the whole of their 

 moisture on Brazil, which, in consequence, is often deluged by 

 the most destructive torrents. This abundant supply, being 

 aided by that vast river system peculiar to the eastern part of 

 South America, and being also accompanied by heat, has stimu- 

 lated the soil into an activity unequaled in any other part of the 

 world. Brazil, which is nearly as large as the whole of Europe, 

 is covered with a vegetation of incredible profusion. A great 

 part of this immense country is filled with dense and tangled 



