340 NATURE AND MAN. 



the Porcupine temperature-soundings seemed to afford conclusive 

 evidence. 



My explanation, though contested by Mr. Croll, and not 

 accepted by Sir Wyville Thomson, has been explicitly adopted by 

 a large number of eminent physicists, both British and Continental, 

 among whom I may specially mention Professor Mohn of Chris- 

 tiania, who had previously maintained the dependence of the re- 

 markable climatic condition of Norway on the north-east extension 

 of the true Gulf Stream. Immediately on receiving the report in 

 which I had demonstrated the inadequacy of the Florida current 

 to propel as far as the coast of Norway the vast body of warm 

 water required to keep its harbours open, and had shown the depen- 

 dence of the north-east movement of the warm upper stratum to 

 the depth of 500 fathoms (which I had myself first recognized in 

 the Porcupine), on the Poleward indraught that forms the 

 necessary complement of the outward glacial underflow, Professor 

 Mohn not only expressed to me his entire concurrence in both 

 views, but communicated to me a remarkable example he had 

 himself met with of a similiar vertical circulation on a smaller 

 scale. It is to the remarkable thickness of this Poleward flow 

 that its surface-layer owes its power of so long resisting the cooling 

 effect of the atmosphere which overlies it; so that, as it flows 

 along the coast of Norway towards the North Cape, its temperature 

 even in winter sustains so much smaller a reduction than that of 

 the atmosphere as to give it an excess which constantly increases 

 with its northing. But though its surface-temperature is so little 

 reduced, the thickness of this warm stratum is undergoing pro- 

 gressive diminution as its deeper layers successively go up to 

 replace those which have been chilled and have gone down ; so 

 that beyond the North Cape the surface-temperature rapidly falls 

 with the eastward movement of this flow along the northern shores 

 of Europe and Asia; and all trace of heat imported from the 

 southwest at last dies out. 



As the superheating of the upper stratum of the mid-x\tlantic is 

 dependent on the influx of Gulf Stream and other water ex- 

 ceptionally warmed in the Equatorial Current, the thermal effect of 

 its north-east flow is mainly dependent upon the Gulf Stream and 

 its adjuncts, while its niovement is kept up by the Polar indraught. 



