62 Temperature Sections Surveyed. 



sinks through the lighter polar current, and the curves present a 

 slow and gradual decrease of temperature from the surface to the 

 bottom (compare Curve B of Station 5, Fig. 4, with the Equatorial 

 Curve, Fig. 9, of Station 110, on the western slope of the 

 central plateau). 



At Station 13 may be observed a remarkable phenomenon, 

 frequently noticed during the progress of the "Challenger" 

 expedition, namely, the simultaneous rise of the isotherms with the 

 sea-bottom. This phenomenon first attracted the attention of the 

 officers of the U.S. Coast Survey as they were engaged in tracing 

 the course of the Labrador current along the coast of the United 

 States. This current was found to rise and fall with the sea-bottom 

 over which it flows, and finally to force its way into the Strait of 

 Florida at the high level of less than 300 fathoms from the 

 surface, immediately below and in a direction contrary to the 

 Gulf Stream current. 



This circumstance seems to indicate that the great thermal 

 currents which, without ceasing, tend to restore the oceanic 

 equilibrium disturbed by the unequal distribution of solar heat, 

 force their way from north to south, and from south to north, 

 against every obstacle to their progress arising from the irregular 

 conformation of the sea-bottom, and from the direction of the coast- 

 lines which cross their path. They rise and fall with the sea- 

 bottom, and accumulate their waters against the shores of islands 

 and continents which stand in their way. There are also indica- 

 tions sufficient to show that the presence of land or submerged 

 areas of elevation is not indispensable to the production of this 

 phenomenon, and that currents flowing side by side but in 

 different directions accumulate their waters against each other, 

 in consequence of which the weaker current gives way to the 

 stronger, and the waters of the lighter current flow over 

 the surface of the heavier current, as is seen in the case of the 

 Gulf Stream, which, along the United States coast, flows over 



