272 THE PHYSICAL GEOGRAPHY OF THE SEA. 



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

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

 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. 



775. Pushing these facts and arguments still farther, these beau- 

 tiful and interesting researches seem already sufficient almost to 

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

 hara, 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. 



776. Lieutenant Jansen has called my attention to a vein of 

 wind which forms a current in the air as remarkable as that of the 

 Gulf; Stream is in the sea. This atmospherical Gulf Stream is in 

 the southeast trade-winds of the Atlantic. It extends from near 

 the Cape of Good Hope, in a direct line to the equator, on the me- 

 ridian of Cape St. Roque (Plate VIII.). The homeward route 

 from the Cape of Good Hope lies in the middle of this vein ; in it 

 the winds are more steady than in any other part of the Atlantic. 

 On the edges of this remarkable aerial current, the wind is vari- 

 able, and often fitful ; the homeward-bound Indiaman resorts to 

 and uses this stream in the atmosphere as the European-bound 

 American does the Gulf Stream. It is shaded on the Plate. 



777. 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 in- 

 land basins of the earth, as compensations in the great system of 

 atmospherical circulation. Like counterpoises to the telescope, 

 which the ignorant regard as incumbrances to the instrument, 

 these wastes serve as make-weights, to give certainty and smooth- 

 ness of motion — facility and accuracy to the workings of the ma- 

 chine. ^ • 



778. 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 



