POPULATION AND CIVILIZATION. 701 



Owing to there being a much larger body of 

 dry land exposed to the influence of a tropical 

 sun in Africa, than in any other part of the world, 

 it has a higher temperature during the hottest 

 part of the day. For it has been shown by Hum- 

 boldt, that the heat of any country is in propor- 

 tion to the extent of fixed surface between lat. 40 

 on each side of the equator, modified by elevated 

 mountains, plains, forests, and sandy deserts. 

 For example, tropical Africa is hotter north than 

 south of the equator ; first, because it is broader 

 north of the equator, from which it narrows on to 

 the Cape of Good Hope ;* and secondly, because 



cipitated in floods of rain, attended with frightful explosions of 

 lightning and peals of thunder. 



* If southern Asia extended over the space now occupied by 

 the Indian ocean, as far as 30 S. interspersed with large sandy 

 deserts, the temperature of tropical India would correspond with 

 that of central Africa, and the whole continent would be conside- 

 rably warmer than at present. Or if instead of narrowing from 

 the United States, on to the isthmus of Darien, North America 

 extended over the space now occupied by the Atlantic as far as the 

 equator, with a breadth of 4000 miles, its climate would have cor- 

 responded very nearly with that of Africa in the same latitudes. But 

 as Africa and Asia contain five or six times more dry land between 

 the latitudes of 40 on each side the Equator, they are warmer, 

 especially Africa, than America in the same parallels. It may 

 also be worthy of notice, that the western coast of tropical Africa 

 is hotter than the eastern coast, which is somewhat cooled by the 

 trade wind, which also moderates the temperature of tropical 

 South America on the east. In the same way, the temperature 

 of Southern Asia is moderated by the monsoons which blow from 

 the Indian ocean during summer. 



