DEEP-SEA DREDGINGS. 149 



results which have been obtained respecting the varying 

 temperatures of deep-sea regions. The peculiarity 

 just considered is, indeed, a consequence of such varia- 

 tions ; but the fact itself is at least as interesting as 

 the consequences which flow from it. It throws light 

 on the long-standing controversy respecting the oceanic 

 circulation. It has been found that the depths of the 

 equatorial and tropical seas are colder than those of the 

 North Atlantic. In the tropics the deep-sea tempera- 

 ture is considerably below the freezing-point of fresh 

 water : in the deepest part of the Bay of Biscay the 

 temperature is several degrees above the freezing-point. 

 Thus one learns that the greater part of the water 

 which lies deep below the surface of the equatorial and 

 tropical seas come from the Antarctic regions, though 

 undoubtedly there are certain relatively narrow 

 currents which carry the waters of the Arctic seas to 

 the tropics. The great point to notice is that the 

 water under the equatorial seas must really have 

 travelled from polar regions. A cold of 30 degrees 

 can be explained in no other way. We see at once, 

 therefore, the explanation of those westerly equatorial 

 currents which have been so long a subject of contest. 

 Sir John Herschel failed to prove that they are due to 

 the trade winds, but Maury failed equally to prove 

 that they are due to the great warmth and consequent 

 buoyancy of the equatorial waters. In fact, while Maury 

 showed very convincingly that the great system of 

 oceanic circulation is carried on despite the winds, 

 Herschel proved in an equally convincing manner that 



