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 1s supplied 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 catside 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 officers 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- 
1 The parallelism of the lines of tem- fluences. See J. J. Wild, *'Thalassa," 
perature is also very marked in the South Plate XV., and “Challenger Tempera- 
Pacifie, where there are no disturbing in- tures." 
