700 INFLUENCE OF CLIMATE ON 



it is deluged with rains for six months, attended 

 with dreadful hurricanes ; and parched with 

 drought during the remainder of the year :* while 

 the frequency of earthquakes and volcanic erup- 

 tions cause the overthrow of many cities, and 

 the destruction of many thousand lives, not to 

 mention the pestilential character of the atmos- 

 phere. Such is the deleterious influence of the 

 torrid zone on the growth of population, that in 

 the vast continent of Africa, it does not exceed 

 57,000,000; or if we take the estimate of Balbi, 

 60,000,000, on a territory of 11,000,000 square 

 miles, a large proportion of which is found above 

 north lat. 30, where the mean temperature of the 

 year varies from 78 to 68, and where conside- 

 rable advances have been made in wealth, civili- 

 zation, arts, science, and social improvements ; as 

 in ancient Egypt, Carthage, and other Phceni- 

 cian states. 



* The reason of which is, that when the sun is south of the 

 equator, there is a perpetual under current of air from the higher 

 and cold latitudes of the northern hemisphere to the tropical 

 zone; where being expanded, it rises loaded with vapour, and 

 flows back as an upper current before the tropical atmosphere 

 becomes saturated, or precipitation takes place, causing a drought 

 of six months on this side of the equator. But when the sun re- 

 turns to the northern hemisphere, the land becomes so heated, even 

 in the higher latitudes, that the under current from the north is 

 greatly diminished, and nearly ceases within the northern tropic. 

 The consequence of which is, that the vapour carried into the at- 

 mosphere, instead of passing with an upper current to the higher 

 latitudes, accumulates within the tropics, and is almost daily pre- 



