78 Te^nperature Sections Surveyed. 



de Verde Islands and the African coast, the other flowing south, 

 past Sierra Leone towards Cape Palmas. At Stations 95, 96, and 

 97, in the direct hne of this cold under-current, the decrease of 

 temperature between the surface and lOO fathoms amounts to 

 15° C. The temperature observations made by the "Chal- 

 lenger" on the return journey at Stations 350, 351, 352, in the 

 same area, off Sierra Leone, prove the same extraordinary 

 decrease of temperature in the first hundred fathoms, amounting 

 respectively to 15°.!, 14°. 3, and 12°. 6 C. The remarkable rise of 

 the isotherm of 2°. 5 C. in this area also deserves to be noticed. 

 At Station 97, the temperature at 1500 fathoms was found to be 

 i°.7 C. Proceeding further north, at Stations 89 and 90, 

 between the Cape de Verde Islands and the Canaries, the tem- 

 perature at 1 100 fathoms was only 3°. 2 C. and 3° C. respec- 

 tively. . At a sounding taken on the 6th February, 1873, 

 between Teneriffe and Madeira, the temperature at 1975 

 fathoms was ascertained to be i°.6 C. ; on February 6th, to the 

 east of Madeira, i°.8 at 2225 fathoms; and on January 30th of 

 the same year, a temperature of i°.6 C. was registered in 1525 

 fathoms, immediately south of the Josephine Bank. 



If we draw a line connecting the western extremities of the 

 plateaux of the Cape de Verde Islands, the Canary Islands, and 

 Madeira, it will be found that the isotherms of the stations west 

 of this line are lower than the isotherms of the stations east of 

 this line, and that, consequently, the water between this line and 

 the coast of Africa is colder than it is to the westward of the 

 above islands. The presence of this cold under-current along 

 the West Coast of Africa, moreover, would be a necessary con- 

 sequence of the general law which governs the circulation of 

 thermal currents. The quantity of cold water supplied to the 

 Atlantic by the Arctic basin is much less than the quantity 

 flowing into it from the Antarctic region, and the principal 

 supply is undoubtedly derived from the latter source. The cold 



