470 CURRENTS AND WHALING. 



The deep-sea temperature near St. Helena proved that the influence 

 even of a submarine polar current was not experienced there. 



It would therefore appear that the South Atlantic is the seat of a 

 system of currents, analogous, but simpler in form, than those of the 

 North. 



Off Cape Horn, we encountered the Great South Polar Stream, 

 whose strength has had such influence on the progress of vessels, and 

 been the cause of so much disaster to the early circumnavigators. 

 This stream spreads far to the eastward, and Cape Horn divides it 

 into two branches, one of which sets along the west coast of South 

 America, far to the northwards. 



The main stream enters the Atlantic, and in the vicinity of Cape 

 Horn is almost as well known as the Gulf Stream on our own coast. 

 It appears to be strongest in the months of August, September, and 

 October, the spring of that hemisphere, and weakest in April and May, 

 or the autumn. It continues its course to the northeast until it appears 

 lost in the South Atlantic, probably sinking beneath the warmer water 

 that has been flowing along the coast of Brazil. Our observations 

 made its greatest velocity seventy-two miles in twenty-four hours, in a 

 direction east-northeast, but its usual rate is about thirty miles in the 

 same time. 



One remarkable feature of the water in the neighbourhood of Cape 

 Horn is its very low temperature at great depths. We found it, as 

 has been stated in Chapter V., as low as 28°, at the depth of four hun- 

 dred fathoms ; and although this great depression of temperature was 

 not exactly verified by other observations, yet those made in the 

 vicinity were sufficiently low to render this remarkable fact probable. 



That the direction of a great body of water to the northward and 

 eastward, is not confined to the vicinity of Cape Horn, we have one 

 proof in the drift of the icebergs, even beyond the line at which a cur- 

 rent is found at the surface, and which must therefore be carried by 

 submarine streams; and another in the observations made by the late 

 French expedition under D'Urville, who found a current setting east- 

 northeast, along the icy barrier to the south of Powell's Group. 



It has been stated that the northeast Polar Stream is divided into 

 two branches at Cape Horn. The Chili branch of the stream at first 

 retains the northeast direction, and sets upon the coast of that country, 

 but as it advances it takes a direction more towards the north. This 

 stream is not superficial merely, but prevails to a great depth, or is 

 submarine. This fact is conclusively shown by an observation of 

 Captain Du Petit Thouars in the French frigate Venus in 1837 ; he 

 found in making a deep-sea sounding in this stream during a calm, 



