220 THE PHYSICAL GEOGRAPHY OF THE SEA. 



blow a regular southwardly monsoon for several months. They 

 bring the rains which divide the season in these parts of the African 

 coast. The region of the ocean embraced by the monsoons is cu- 

 neiform in its shape, having its base resting upon Africa, and its 

 apex stretching over till within 10° or 15° of the mouth of the 

 Amazon. 



468. Indeed, when we come to study the effects of South Amer- 

 ica and Africa (as developed by the Wind and Current Charts) 

 upon the winds at sea, we should be led to the conclusion — had 

 the foot of civilized man never trod the interior of these two con- 

 tinents — that the climate of one is humid ; that its vallevs are, 

 for the most part, covered with vegetation, which protects its ^^ur- 

 face from the sun's rays ; while the plains of the other are arid 

 and naked, and, for the most part, act like furnaces in drawing the 

 winds from the sea to supply air for the ascending columns which 

 rise from its overheated plains. 



469. Pushing these facts and arguments still farther, these 

 beautiful and interesting researches seem already sufficient almost 

 to justify the assertion that, were it not for the Great Desert of 

 Sahara, and other arid plains of Africa, the western shores of that 

 continent, within the trade-wind region, would be almost, if not 

 altogether, as rainless and sterile as the desert itself. 



These investigations, with their beautiful developments, eagerly 

 captivate the mind ; giving wings to the imagination, they teach 

 us to regard the sandy deserts, and arid plains, and the inland ba- 

 sins of the earth, as compensations in the great system of atmos- 

 pherical circulation. Like counterpoises to the telescope, which 

 the astronomer regards as incumbrances to his instrument, these 

 wastes serve as make-weights, to give certainty and smoothness 

 of motion — facility and accuracy to the w^orkings of the machine. 



470. When we travel out upon the ocean, and get beyond the 

 influence of the land upon the winds, we find ourselves in a field 

 particularly favorable for studying the general laws of atmospher- 

 ical circulation. Here, beyond the reach of the great equatorial 

 and polar currents of the sea, there are no unduly heated surfaces, 

 no mountain ranges, or other obstructions to the circulation of the 

 atmosphere — nothing to disturb it in its natural courses. The sea, 

 therefore, is the field for observing the operations of the general 

 laws which govern the movements of the great aerial ocean. Ob- 



