182 THE FITNESS OF THE ENVIRONMENT 



west to east; in the north a current flows 

 from east to west, from the Siberian coast 

 to Northeast Greenland and thence along the 

 east coast; another flows from Baffin's Bay 

 along the east coast of North America. 



Of all ocean currents, the Gulf Stream, a 

 branch of the northern .equatorial current, 

 has been most carefully studied. Its maxi- 

 mum velocity is 220 kilometers per day, 

 greater therefore than that of the Rhine at 

 Coblentz ; the mean about 134 kilometers a 

 day. In the Straits of Yucatan the Gulf 

 Stream carries 0.2 cubic kilometer (200,000,- 

 000 tons) per second. If all this water were 

 to be cooled to the temperature of the polar 

 ocean this would be equivalent to the trans- 

 port of about 5,000,000,000,000,000 gram 

 calories per second. The magnitude of this 

 quantity, of course, depends upon the specific 

 heat of water. 



In this manner vast quantities of water, 

 | carrying enormous stores of heat, are constantly 

 I in motion all over the globe. The result is 

 that homogeneity of the ocean which has been 

 discussed above, — constancy of concentra- 

 tion, of composition, of temperature, of alka- 

 linity, and of osmotic pressure. 



