370 THE DEPTHS OF THE SEA. [chaf. vm. 



by this the body of superheated water which issues 

 through the 'narrows' from the Gulf of Mexico), if 

 it reaches this locality at all— which is very doubtful 

 — could only affect the most superficial stratum ; and 

 the same may be said of the surface-drift caused 

 by the prevalence of south-westerly winds, to which 

 some have attributed the phenomena usually ac- 

 counted for by the extension of the Gulf-stream to 

 these regions. And the presence of the body of 

 water which lies between 100 and 600 fathoms depth, 

 and the range of whose temperature is from 48° 

 (8°-85 C.) to 42° (5°'5 C), can scarcely be accounted 

 for on any other hypothesis than that of a great 

 general movement of equatorial water towards the 

 polar area, of which movement the Gulf-stream con- 

 stitutes a peculiar case, modified by local conditions. 

 In like manner the arctic stream which underlies 

 the warm superficial strata in our cold area, con- 

 stitutes a peculiar case, modified by the local condi- 

 tions, to be presently explained, of a great general 

 movement of polar water towards the equatorial 

 area, which depresses the temperature of the deepest 

 parts of the great oceanic basins nearly to the 

 freezing-point." ^ 



At first Dr. Carpenter appears to have regarded 

 this oceanic circulation as a case of simple convection. 

 " To what, then, is the north-east movement of the 

 warm upper stratum of the North Atlantic attri- 

 butable ? I have attempted to show that it is part 

 of a general interchange between polar and equa- 

 torial waters, which is quite independent of any such 



1 A Lecture delivered at the Eoyal Institution, abstracted with 

 the Author's signature in Nature, vol. i. p. 488 (March 10th, 1870). 



