ON THE PHYSICAL THEOEY OF rNDER-CUHltENTS. 155 



a more free passage for an interchange of water. 



The author, in conclusion, pointed out that many of the facts 

 discovered by the Challenger had been predicted by Dr. Carpenter 

 as necessary deductions from the theory of Oceanic Circulation, 

 and claimed support for it on this ground. He argued that this 

 great vertical circulation could not be either set on foot or kept 

 u p by the mere action of wind and solar heat at the surface, as 

 was maintained by the supporters of the Gulf stream theory ; and 

 he contended that polar cold was a far more potent agent in 

 producing it, since the surface water as it cooled down sank to 

 the bottom, thus establishing at once a vertical movement, while 

 its place was immediately supplied by an indraught of warmer 

 surface water. The amelioration of climate of E'.W. Europe, 

 therefore, was due, not to the Gulf stream — a mere surface 

 cu rrent, which lost itself in the North Atlantic, and was broken 

 up before it reached 33" W. long. — but to the north-easterly 

 movement of a vast body of water 1,700 miles wide, and at least 

 600 fms. deep, as was shown by the fact that the Bathymetrical 

 isotherms of 45^" and 40"^ scarcely changed their position between 

 Portugal, where they were below the normal, and the Faroe 

 Islands, where they were above it. The only possible inference 

 from this was that there was a northward movement of the whole 

 stratum, to which an easterly direction was given by the earth's 

 rotation, since the water at the equator was moving at a greater 

 rate from "W. to E. than the water north of it, and hence water 

 coming from the equator, and bringing an increased easterly 

 momentum, had a tendency to go towards the east. 



