XCV1 NOTES. 



Novo, Bas. 1523, Dec. iii. lib. vi. p. 57. Sea Humboldt, Exaraen critique* 

 T. ii. pp. 254257, and T, iii. p. 108. 



(V*) p. 301. Humboldt, Examen crit. iii. pp. 64109. 

 [M. de Humboldt has not noticed the important and philosophical classifi- 

 cation of currents, according to their origin, into drift and stream currents, 

 introduced by the late Major Rennell, in his Investigation of the Currents of 

 the Atlantic Ocean, p. 21, Lond. 1832 ; a distinction most necessary to be 

 borne in mind, when inquiring into or discussing the history of any particular 

 current. According to this classification, a drift current is the effect of a con- 

 stant or of a very prevalent wind on the surface water of the ocean, impelling 

 it to leeward until it meets with some obstacle which stops it, and occasions an 

 accumulation, the accumulation giving rise to a stream current : the obstacle 

 may be either land or banks, or a stream current already formed. A stream 

 current is the flowing off of the accumulated waters of a drift current, caused 

 by the effort of the water to restore the equilibrium of the general level surface 

 of the ocean. A stream current may be of any bulk, or depth, or velocity ; a 

 drift current is shallow, and rarely exceeds in velocity the rate of half a mile an 

 hour. When drift currents are opposed by a stream already formed, they 

 either fall into it and augment it, if the angle which their direction makes 

 with that of the stream current be less than a right angle ; or if it be greater, 

 the drift current itself forms a stream current, which takes a parallel but oppo- 

 site course to that of the stream by which its progress has been stopped. 

 Thus the equatorial current referred to in the text, which flows from the ac- 

 cumulated waters in the bend of the western coast of Africa near the Bight 

 of Benin, is banked up on its southern side, in its passage across the Atlantic, 

 by the drift current impelled by the S.E. trade-wind, which current falls into 

 and continually augments the equatorial stream, maintaining it in such strength 

 that, on its arrival on the Brazilian coast, it is able to furnish the two great 

 branches into which it is divided by Cape St. Roque, the N.E. promontory of 

 South America, one branch pursuing its course to the Caribbean Sea, and the 

 other running southward along the coast of South America to Cape Horn. 

 It appears to require a further investigation to decide whether the stream 

 current, referred to in the text, which flows along the coast of Norway and 

 round the North Cape of Europe, and is, at least, mainly supplied from the 

 accumulated waters of the drift impelled by the west and south-west winds 

 which prevail to the northward of the trades, derive any portion whatsoever 

 of its force from the original impulse given to the waters of the gulf-stream 

 at its outlet from the Gulf of Mexico, in the Bahama Channel. The transport 



