178 Mr. J. Croll on the Physical Cause of Ocean-currents. 



portion trending northwards and the other southwards. The 

 northern branch of the equatorial current of the Atlantic passes* 

 into the Caribbean Sea, and after making a circuit of the Gulf 

 of Mexico, flows northward and continues its course into the 

 Arctic Ocean. The southern branch, on the other hand, is de- 

 flected along the South-American coast, constituting what is 

 known as the Brazilian current. In the Pacific a similar deflec- 

 tion occurs against the Asiatic coast, forming a current some- 

 what resembling the Gulf-stream, a portion of which (Kamt- 

 schatka current) in like manner passes into the Arctic regions. 

 In reference to all these various currents, the impelling cause 

 is supposed to be the force of the trade- winds. 



It is, however, urged as an objection by Maury and other ad- 

 vocates of the gravitation theory, that a current like the Gulf- 

 stream, extending as far as the Arctic regions, could not possibly 

 be impelled and maintained by a force acting at the equatorial 

 regions. But this is a somewhat weak objection. It seems to 

 be based upon a misconception of the magnitude of the force in 

 operation. It does not take into account that this force acts on 

 nearly the whole area of the ocean in intertropical regions. If, 

 in a basin of water, say three feet in diameter, a force is applied 

 sufficient to produce a surface-flow one foot broad across the 

 centre of the basin, the water impelled against the side will be 

 deflected to the extremes of the vessel. And this result does 

 not in any way depend upon the size of the basin. The same 

 effect which occurs in a small basin will occur in a large one, 

 provided the proportion between the breadth of the belt of water 

 put in motion and the size of the vessel be the same in both 

 cases. It does not matter, therefore, whether the diameter of the 

 basin be supposed to be three feet, or three thousand miles, or 

 ten thousand miles. 



There is a more formidable objection, however, to the theory. 

 The trade- winds will account for the Gulf-stream, Brazil, Japan, 

 Mozambique, and many other currents ; but there are currents, 

 such as some of the polar currents, which cannot be so accounted 

 for. Take, for example, the great Antarctic current flowing 

 northward into the Pacific. This current does not bend to the 

 left under the influence of the earth's rotation and continue its 

 course in a north-westerly direction, but actually bends round 

 to the right and flows eastward against the South- American coast, 

 in direct opposition both to the influence of rotation and to the 

 trade- winds. The trade- wind theory, therefore, is insufficient to 

 account for all the facts. But there is yet another explanation, 

 which satisfactorily solves our difficulties. The currents of the 

 ocean owe their origin, not to the trade-winds alone, but to the 

 prevailing winds of the globe (including, of course, the trade- 

 winds) . 



