132 The Colour of the Sea 



is usually attributed to the Labrador current, which is charged 

 with the duty of bringing cold water from Baffin's Bay as 

 a surface current round Newfoundland and down the coast 

 to Cape Hatteras and even beyond it. The principle was 

 the same as that which moved Humboldt to attribute the 

 cold water, which we have described in connection with the 

 Pacific coast of tropical South America, to a surface current 

 from the Antarctic Ocean. In my paper "On Similarities," 

 etc., I have shown that Humboldt's explanation postulated 

 an impossibility. The deeper layers of the water on the 

 coast itself are capable of supplying, as and when required, 

 much more cold than is wanted, and that with the least 

 expenditure of energy. The same is the case with the 

 "cold wall." Besides the south-westerly winds of the North 

 Atlantic, and perhaps independently of them, the Gulf Stream 

 itself, pouring its waters in a stream of great momentum past 

 the American coast and out into the open ocean, performs 

 the function of a colossal jet-pump, carrying water away 

 from the surface and leaving its place to be taken by the other 

 water which can get there most easily. This is the cold water 

 of the deeper layers in situ. It is this hydraulic cold-water 

 service which tempers the climate of the eastern States. The 

 labours of the U.S. Coast Survey during the last seventy 

 years have shown that fluctuations, both regular and irregular, 

 occur in the flow of the Gulf Stream. These necessarily 

 re-act on the supply of cold water drawn from the deep and 

 spread over the continental shelf. Such variations are probably 

 the source of the accidents which occasionally occur and 

 cause the extinction of marine life over large tracts of shoal 

 water on that coast 1 . 



1 See Contents, p. xxv. 



