114 THE PHYSICAL GEOGRAPHY OF THE SEA. 



Porter, in the steam-ship Golden Age, found the heaviest water 



about the parallels of 20° north and 17° south. Captain Kodgers, 



in the United States ship Yincennes, found the heaviest water in 



17° K, and between 20° and 25° S. 



294. In summing up the evidence in favor of this view of the 



Seeing that the south- general svstem of atmospherical circulation, it re- 

 em hemisphere af- . "l ^ ^ . . . ^ , . , 



fords the largest maius to DC showu how it IS, II thc vicw DC corrcct, 



evaporating surface, ^ ^^^^ . .., 



how, unless there be tncrc snould DC Smaller rivcrs and less ram m the 



a crossing, could we , ^ • ^ mi • i i i i 



have most rain and southem hemisphere. The winds that are to blow 

 the northern? as the northcast trade- winds, returning from the 



polar regions, where the moisture (§ 292) has been compressed out 

 of them, remain, as we have seen, dry winds until they cross the 

 calm zone of Cancer, and are felt on the surface as the northeast 

 trades. About two thirds of them only can then blow over the 

 ocean ; the rest blow over the land, over Asia, Africa, and North 

 America, where there is comparatively but a small portion of 

 evaporating surface exposed to their action. The zone of the 

 northeast trades extends, on an average, from about 29° north to 

 7° north. Now, if we examine the globe, to see how much of 

 this zone is land and how much water, we shall find, commencing 

 with China and coming over Asia, the broad part of Africa, and 

 so on, across the continent of America to the Pacific, land enough 

 to fill up, as nearly as may be, just one third of it. This land, if 

 thrown into one body between these parallels, would make a belt 

 equal to 120° of longitude by 22° of latitude, and comprise an 

 area of about twelve and a half millions of square miles, thus 

 leaving an evaporating surface of about twenty -five millions of 

 square miles in the northern against about seventy -five millions 

 in the southern hemisphere. According to the hypothesis, illus- 

 trated by Plate I., as to the circulation of the atmosphere, it is 

 these northeast trade-winds that take up and carry over, after they 

 rise up in the belt of equatorial calms, the vapors which make 

 the rains that feed the rivers in the extra-tropical regions of the 

 southem hemisphere. Upon this supposition, then, two thirds 

 only of the northern trade-winds are fully charged with moisture, 

 and only two thirds of the amount of rain that falls in the north- 

 ern hemisphere should fall in the southern ; and this is just about 

 the proportion (§ 292) that observation gives. In like manner, 

 the southeast trade-winds take up the vapors which make our 



