370 THE DEPTHS OF THE SEA. [CHAP. vin. 



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 0.), 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." 1 



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 Royal Institution, abstracted with 

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



