244 THREE CRUISES OF THE " BLAKE." 



seen clearly in the northerly extension of the isothermal lines. 

 In the South Atlantic/ owing in part to the greater regularity 

 in the shape of the basin, the difference in the extension of the 

 isothermal lines is but little marked. 



The temperature sections of the " Challenger," from Tene- 

 riffe to Sombrero, show remarkably well the great contrast in 

 temperature between the eastern and. western basins of the At- 

 lantic, which are separated by the Dolphin Rise. In the eastern 

 basin, the cold water on the bottom is suppHed by the indraught 

 from the South Atlantic, while the warmer surface water of the 

 western basin is due to the westerly equatorial currents. We 

 seem, therefore, to have masses of water of different temper- 

 atures accumulated at certain points by surface or bottom cur- 

 rents, to be distributed again, either north or south, into the 

 general oceanic circulation, thus restoring the equilibrium dis- 

 turbed by the unequal distribution of heat and cold on the sur- 

 face of the ocean. 



Another temperature section (Fig. 170) which I shall borrow 

 from the " Challenger " soundings, to complement the work of 

 the " Blake " in the same regions, is that which extends from 

 Halifax to the Bermudas, and thence to St. Thomas. The 

 temperatures observed by these vessels show plainly the path of 

 the warm surface-water, which flows outside of the West India 

 Islands, and joins the Gulf Stream proper, whose waters when 

 united are banked against the cold Labrador current in its course 

 along the American coast. 



Undoubtedly, the early observations made upon the temper- 

 ature of the ocean were defective, owing to the somewhat im- 

 perfect instruments at the disposal of the early explorers. Yet 

 they determined the general position of the cold and warm cur- 

 rents of the ocean along our shores. The more systematic work 

 of the of&cers of the Coast Survey first proved the existence of 

 vast bodies of water, of considerable thickness, and of very dif- 

 ferent temperatures at corresponding depths, moving in opposite 

 directions. It is to the Coast Survey that we owe the demon- 



^ The parallelism of the lines of tem- fliiences. See J. J. Wild, " Thalassa," 

 peratiire is also very marked in the South Plate XV., and " Challenger Tempera- 

 Pacific, where there are no disturbing- in- tures." 



