196 J. D. Dana on an Isothermal Oceanic Chart, 



Islands. The line passes to the south of these islands, at 

 which group Fitzroy, in January of 1852, found the sea- 

 temperatures 71° and 72° F. 



Isocryme of 68° F. — Cape Canaveral, in latitude 27° 30', 

 just north of the limit of coral reefs on the east coast of 

 Florida, is the western termination of the line of 68°. The 

 Gulf Stream occasions a bend in this line to 36° north, and 

 the polar current, east of it, throws it southward again as 

 far as 29° north. Westward it inclines much to the south, 

 and terminates just south of Cape Verde, the eastern cape 

 of Africa. Sabine found a temperature of 64° to 65° F. off 

 Goree, below Cape Verde, January 1822 ; and on February 

 9, 1822, he obtained 66^° near the Bissao shoals. These 

 temperatures of the cold season contrast strikingly with 

 those of the warm season. Even in May (1831) Beechey 

 had a temperature of 86° off the mouth of Rio Grande, be- 

 tween the parallels of 11° and 12° north. 



Isocryme of 62° F. — This isocryme leaves the American 

 coast at Cape Hatteras, in latitude 35 J° north, where a bend 

 in the outline of the continent prevents the southward ex- 

 tension of the polar currents close along the shores. It 

 passes near Madeira and bends southward, reaching Africa 

 nearly in the latitude of the Canaries. 



Isocrymes of 56° and 50° F. — Cape Hatteras, for a like 

 reason, is the limit of the isocrymes of 56° and 50° as well 

 as of 62°, there being no interval between them on the 

 American coast. The line of 56° F. has a deep northward 

 flexure between the meridians of 35° and 40° west, arising 

 from the waters of the Gulf Stream, which here (after a 

 previous east and west course, occasioned by the Newfound- 

 land Bank, and the Polar current with its icebergs) bends 

 again north-eastward, besides continuing in part eastward. 

 The Polar current sometimes causes a narrow reversed flex- 

 ure, just to the east of the Gulf Stream flexure. Towards 

 Europe, the line bends southward, and passes to the south- 

 west cape of Portugal, Cape St Vincent, or perhaps to the 

 north cape of the Straits of Gibraltar. Vaillant, in the 

 Bonite, found the sea-temperature at Cadiz in February, 49 J° 

 to 56° F. (9-7° to 13-4° C), which would indicate that Cadiz, 



