SUA ROUTES, CALM BELTS, AND VARIABLE WINDS. 363 



that the climate of one is liiimicT ; that its valleys are, for the 

 most part, covered with vegetation, which protects its surface 

 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 over-heated plains. 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 gi*eat desert of Sahara and other arid ])lains 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. 



C77. A '' G-ulf Stream " in the air. — 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 south-east trade-winds of the 

 Atlantic. It extends from near the Cape of Good Hope, in 

 a direct line to the equator, on the meridian of Cape St. Eoque 

 (Plate VIII.). The homew^ard 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 variable 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. 



678. Counterpoises. — These investigations, with their beautiful 

 developments, eagerly captivate the mind ; giving wings to the 

 imagination, they teach us to regard the sand}^ deserts, and arid 

 plains, the mountain ranges, and the inland 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 smoothness of motion — facility 

 and accuracy to the workings of the machine. 



079. Normal state of the atmosphere, ^^\hen we travel out upon 

 the ocean, and get beyond the influence of the land upon the 

 winds, we find ourselves in a field particularly favourable for 

 studying the general laws of atmospherical circulation. Here, 

 beyond the reach of the great equatorial and polar currents of 

 the sea, there are no unduly heated surfaces, no mountain ranges, 



