1872.] 



' Shearwater 9 Scientific Researches. 



551 



20. All these facts (of which Mr. Croll has not even attempted to offer 

 a rationale) are brought into harmonious relation by the doctrine of 

 a General vertical Oceanic Circulation, from which the Mediterranean 

 and other Inland Seas are excluded (u.) in virtue of the shallowness of 

 their communications with the general Ocean-system. For (i.) the hori- 

 zontal division of the Atlantic into two strata separated by a marked dif- 

 ference of temperature is thus accounted for, if the upper be conceived as 

 slowly creeping from the Equator towards the Pole, whilst the lower creeps 

 as slowly from the Pole towards the Equator. Next, it fully explains the 

 glacial temperature of the Deep-sea bottom (iv.), which, as the cases of 

 the Mediterranean and the Sulu Sea clearly prove, cannot be attributed to 

 depth per se. Again, it gives an adequate reason for the relatively low 

 temperature of the whole mass of Tropical water beneath 200 fathoms 

 depth (in.) ; this having been drawn into the Tropical area as glacial 

 water, and having risen towards the surface as it received warmth from the 

 crust of the earth on which it rests'; the warmer stratum above it being 

 drafted away towards the Pole, whilst its place is taken beneath by a fresh 

 arrival of colder water from the Pole. Further, it affords an adequate 

 rationale for the great body of facts now known (vi.) regarding the ab- 

 normally high temperatures met with between Greenland, Iceland, and the 

 coast of Northern Europe ; for which the ordinary hypothesis of the ex- 

 tension of the Florida Current or true Gulf-stream into that region fails 

 to account, as will be shown in Appendix I. to this Report. The Ver- 

 tical Circulation is (as it were) epitomized in the "Lightning Channel ;" in 

 which there is evidence, from Nautical Observation, of the N.E. movement 

 of the upper warm stratum (vi.) ; whilst there is inferential evidence of the 

 S.W. movement of the glacial stratum beneath (v.). — Although no experi- 

 mental evidence has yet been obtained, either of this movement, or of the 

 flow of the deeper stratum of Oceanic water generally from the Polar basins 

 towards the Intertropical zone, indications of such a movement are not 

 wanting. The descent of Icebergs into comparatively low latitudes, in op- 

 position to the current of the Gulf-stream, has been frequently recorded. 

 Two instances of this kind are cited by Dr. Hayes, as having fallen under 

 the notice of Capt. Courtney. On the 27th of April, 1829, he passed an 

 iceberg from 80 to 100 feet high, in N. Lat. 36° 10' and W. Long. 39°; 

 and on the 17th of August, 1831, he met with another in N. Lat. 36° 20' 

 and W.Long. 47° 45'; both having been carried further south than the 

 southern edge of the Gulf-stream, which they must thus have crossed. 

 — So, again, according to the statement of Mr. Newall, of Gateshead (kindly 

 communicated to me by Sir Henry Rawlinson), a red-painted buoy, which 

 was attached by a wire rope to the end of the Atlantic Cable cut adrift in 

 1865, in N. Lat. 51° 28' and W. Long. 38° 42', was seen seventy-six days 

 afterwards in Lat. 42°, Long. 40° ; so that it had travelled nearly due south 

 about GOO nautical miles, or about eight nautical miles a day. Though it 

 cannot be affirmed with certainty that this change of place was due to the 



vol. xx. 2 s 



