DEEP-SEA DREDGIXGS. 105 



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 comes 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 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 

 the overflow conceived by Maury should result in an 

 easterly instead of a westerly current. Recently the 

 theory was put forward that the continual process of 



