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



cither in impelling the currents, or in determining which shall 

 be the upper and which the lower. 



The wind in Baffin's Bay and Davis Strait blows nearly 

 always in one direction, viz. from the north. The tendency 

 of this is to produce a surface- or upper current from the north 

 down into the Atlantic, and to prevent or retard any surface- 

 current from the south. The warm current from the Atlantic, 

 taking the path of least resistance, dips under the polar current 

 and pursues its course as an under current. 



Mr. Clement Markham, in his ' Threshold of the Unknow r n 

 Region/ is inclined to attribute the motion of the icebergs to 

 tidal action or to counter undercurrents. That the motion of the 

 icebergs cannot reasonably be attributed to the tides is, I think, 

 evident from the descriptions given both by Midshipman Griffin 

 and by Captain Duncan, who distinctly saw the icebergs moving 

 at the rate of about four knots an hour against a surface-current 

 flowing southwards. And Captain Duncan states that the bergs 

 continued their course northwards for several days, till they 

 ultimately disappearedt. The probability is that this north- 

 ward current is composed partly of Gulf-stream water and 

 partly of that portion of polar water which is supposed to flow 

 round Cape Farewell from the east coast of Greenland. This 

 stream, composed of both warm and cold water, on reaching to 

 about latitude 65° N., where it encounters the strong northerly 

 winds, dips dow T n under the polar current and continues its 

 northward course as an under current. 



We have on the west of Spitzbergen, as has already been 

 noticed, a similar example of a warm current from the south 

 passing under a polar current. A portion of the Gulf-stream 

 which passes round the west coast of Spitzbergen flows under an 

 Arctic current coming down from the north ; and it does so no 

 doubt because it is here in the region of prevailing northerly 

 winds, which favour the polar current but oppose the Gulf- 

 stream. Again, we have a cold and rapid current sweeping 

 round the east and south of Spitzbergen, a curreni of which 

 Mr. Lamont asserts that he is positive he has seen it running 

 at the rate of seven or eight miles an hour. This current, on 

 meeting the Gulf-stream about the northern entrance to the 

 German Ocean, dips down under that stream and pursues its 

 course southwards as an under current. 



Several other cases of under currents might be adduced which 

 cannot be explained on the gravitation theory, and which must 

 be referred to a system of oceanic circulation produced by the 

 impulse of the wind; but these will suffice to show that the 

 assumption that the winds can produce only a mere surface-drift 

 is directly opposed to facts. And it will not do to affirm that a 



