1478 CRUSTACEA. 



These are important principles modifying the courses of the oceanic 

 isothermal lines ; we may now proceed to the application of them. 



In the Atlantic, the warm tropical current flowing westward, is 

 trended somewhat northward by the northern coast of South America, 

 and still more so by the West India Islands, and thus it gradually 

 curves around to parallelism with the coast of the United States. But 

 south of Newfoundland, either wholly from the influence of the colder 

 current which it meets with, or in part from meeting with submarine 

 slopes that serve to deflect it, it passes eastward, and afterwards, 

 where it is again free to expand, it spreads both eastward and north- 

 eastward. The flexures in the isocrymes of 74 and 68 F., near the 

 United States coast, thus have their origin. For the same reason, the 

 line of 56 F. is nearly straight, till it reaches beyond the influence of 

 the Newfoundland Banks, and then makes its Gulf Stream flexure. 

 The line of 44 F. for the same reason, the spreading of the Gulf- 

 Stream waters diverges far from the equator in its easterly course, 

 and even rises in a long loop between Great Britain and Iceland. 



The cold currents, flowing down the eastern coast of America, bend 

 the isocrymes far south close along the coast, and make a remarkable 

 southern . flexure in the isocrymes of 68 and 56 F. outside of the 

 Gulf Stream flexure. So on the western coast of Britain, the isocryme 

 of 44 F. has a deep southern flexure, for a like cause. 



The waters of the tropical current gradually cool down in their 

 progress, through the influence of the colder waters which they en- 

 counter; and along the isocryme of 62, they have in the colder 

 seasons a common temperature with that of the ocean, so that the 

 course of the Gulf Stream is but faintly marked in it. And also in 

 the western half of the region covered by the isocryme of. 56, the 

 colder and warmer waters have reached this as a mean temperature. 

 Owing to the influence of the polar current on the northern coast of 

 South America, the equator of heat lies at a distance from the land. 



Up the western coast of Africa flows the cold current from the 

 south and west, bending upward all the isocrymal lines; and passing 

 north of the equator, it produces a large southern bend, off the coast 

 of Africa, in the northern isocryme of 74 outside of the warm current 

 flexure from the coast of Guinea, and also a large northern flexure in 

 the heat-equator.* 



* Along the ocean, near Africa, south and southeast of the Cape Verdes, Captain Wilkes 

 found a current setting to the northward for much of the time until passing the equator. 



