GENERAL FEATURES OF THE EARTH. 41 



earth rotates to the eastward, the westward tropical flow is due 

 simply to a slight lagging of the waters in those latitudes. But 

 transfer these waters towards the pole, where the earth's surface 

 moves less rapidly (the rate of motion varies as the cosine of lati- 

 tude), and then they may move faster than the earth's surface and 

 so have a movement to eastward. Thus, the tropical current from, the 

 east becomes an eastward one, or from the ivest, by mere change of 

 latitude ; and at some point intermediate there would be a region 

 of no east-and-west movement. Any cause producing motion from 

 the equator towards the poles, and the reverse, would therefore 

 bring about the tropical and extratropical movements. On the 

 same principle, any waters flowing from the polar regions (where 

 the earth's motion at surface is slow) towards the equator would be 

 thrown mainly against the west side of the oceans (as the Labrador 

 current in the North Atlantic), for they have no power to keep 

 up with the earth's motion. But the waters flowing towards the 

 pole, that have not lost much of their previous eastward-moving 

 force, may descend to lower latitudes along the east side of 

 the ocean. 



43. Put the above figure in either the Atlantic or Pacific, and 

 the system for the ocean will be apparent at a glance. 



In the North Atlantic the deep tropical current from the east is 

 turned to the northward along the West India islands, and it there 

 becomes the Gulf Stream ; it flows by Florida to the northeast, fol- 

 lowing nearly the outline of the oceanic basin (§ 17) ; it passes the 

 Newfoundland bank, and stretches over towards Europe ; then a 

 part bends southeastward to join the tropical current and complete 

 the ellipse ; the centre of this ellipse is the Sargasso Sea, abounding 

 in seaweeds and calms. Another large portion continues on north- 

 eastward over the region between Britain and Iceland to the poles. 

 From the polar region it returns along by Eastern Greenland, Davis' 

 Straits, and other passages, pressing against the North American 

 coast, throwing cold water into the Gulf of St. Lawrence, bringing 

 icebergs to the Newfoundland banks, and continuing on southward 

 to the West India islands and South American coast, where it pro- 

 duces slight effects in the temperature of the coast-waters. Cape 

 Cod stands out so far that the influence of the cold current is less 

 strongly felt on the shores south than north ; and Cape Hatteras 

 cuts off still another portion. 



In the South Atlantic there is the tropical flow from the east ; 

 the bending south towards Rio Janeiro ; the turn across towards 

 Cape of Good Hope ; and the bending again northward of the 

 waters now cold. But, owing to the manner in which the channels 



