1869.] on the Scientific Exploration of the Deep Sea. 463 



103. Thus the doctrine of a general interchange between Polar and Equa- 

 torial Waters (§ 92) seems the only hypothesis that is competent to account 

 for the facts of this case*; and it will be found to derive further support 

 from the Temperature-phenomena of the North-Atlantic basin, which we 

 shall presently discuss on the basis of the Thermometric observations taken 

 in the First and Second Cruises of the 'Porcupine,' with additional evidence 

 from other sources. — Before proceeding to these, however, we shall inquire 

 whether any rationale can be given for the special peculiarity of the Arctic 

 current, which produces the depression of temperature to from 32°-30° 

 everywhere noticeable at depths of from 300-640 fathoms in our Cold area. 



104. A glance at the North Polar region, as laid down either on a Globe, 

 or on any projection of which the Pole is the centref, — as in the accom- 

 panying Chart (Plate 7) shows that the Polar Basin is so much shut-in by 

 the northern shores of the European, Asiatic, and American Continents, 

 that its only outlet, besides the narrow and shallow channel of Behring's 

 Straits, .and the circuitous passages leading into Hudson's and Baffin's 

 Bays, is the space which intervenes between the eastern coast of Green- 

 land and the north-western coast of the Scandinavian Peninsula. If, 

 therefore, there be any such general movement of ice-cold water towards 

 the Equatorial regions as that for which we have argued, this movement 

 must take place mainly through the deeper portions of this interspace ; 

 at the north of which lies Spitzbergen, whilst Iceland and the Faroes 

 lie in the middle of its southerly expanse. Now in the western portion of 

 this channel, lying between Greenland and Iceland, the depth of water for 

 the most part ranges from 800 fathoms to nearly double that amount ; 

 and there will here, therefore, be a free exit to the water which has been 

 cooled down within the Arctic basin, and has consequently subsided to its 

 deeper portions. But on the eastern side of Iceland the case is very dif- 



* The existence of " Polar Currents " beneath the heated waters of Tropical regions 

 had been indicated by various observers (see 'Lightning' Report, p. 186); but they 

 seem to have been generally, if not universally, regarded as local peculiarities. Con- 

 versely, a movement of Equatorial water in the Polar direction, quite independent of 

 such local accidents as those which produce the Gulf-stream proper, had been noticed 

 in several localities ; particularly between the Indian and Antarctic Oceans (see 

 Maury's 'Physical Geography of the Sea,' §§ 748-750), where the whole movement 

 is forced to take place towards the South pole, by the barrier interposed by the Con- 

 tinent of Asia to any flow in a northerly direction. — The real import of such facts as 

 these could not be recognized by Physical Geographers, so long as they were under the 

 " dominant idea" of a uniform deep-sea temperature of 39°; and our present endeavour 

 is simply to show that the doctrine of Oceanic circulation, being at the same time in 

 accordance with Physical theory (as laid down by Prof. Buff), and consonant with all 

 the reliable facts yet observed, is entitled to the same rank as a fundamental principle 

 in the science of Physical Geography, as the parallel doctrine of Atmospheric circulation 

 holds in Meteorology. 



f The ordinary Hemispherical projection of our Atlases does not give by any means a 

 correct idea of this Polar Basin ; and the Mercator's projection (which is employed by 

 Dr. Wallich) so exaggerates the Longitude-distances in high Latitudes, as to give an 

 entirely fallacious conception of it. 



2 n 2 



