Mr. J. Croll on the Physical Cause of Ocean- currents. 107 



Iceland from Greenland. The observations which have already 

 been made, however, show that nearly the entire channel is oc- 

 cupied, on the surface at least, by water flowing southward from 

 the polar area — a direction the opposite of what it ought to be 

 according to the gravitation theory. In fact the surface of one 

 half of the entire area of the ocean, extending from Greenland to 

 the North Cape, is moving in a direction the opposite of that 

 which it ought to take according to the theory under review. 

 The western half of this area is occupied by water which at the 

 surface is flowing southwards; while the eastern half, which has 

 hitherto been regarded by almost everybody but Dr. Carpen- 

 ter himself and Mr. Findlay as an extension of the Gulf-stream, 

 is moving polewards. The motion of the western half must be 

 attributed to the winds and not to gravity ; for it is moving in 

 the wrong direction to be accounted for by the latter cause; but 

 had it been moving in the opposite direction, no doubt its motion 

 would have been referred to gravitation. To this cause the mo- 

 tion of the eastern half, which is in the proper direction, is 

 attributed* ; but why not assign this motion also to the impulse 

 of the winds, more especially since the direction of the prevail- 

 ing winds blowing over that area coincides with that of the water? 

 If the wind can produce the motion of the water in the western 

 half, why may it not do the same in the eastern half ? 



If there be such a difference of density between the equatorial 

 and polar water as to produce a general flow of the upper portion 

 of the ocean poleward, how does it happen that one half of the 

 water in the above area is moving in opposition to gravity ? 

 How is it that in a wide open sea gravitation should act so pow- 

 erfully in the one half of it and with so little effect in the other 

 half? There is probably little doubt that the ice-cold water 

 of the western half extends from the surface down to the bot- 

 tom. And it is also probable that the bottom-water is moving 

 southwards in the same direction as the surface-water. The 

 bottom-water in such a case would be moving in harmony with 

 the gravitation theory ; but would Dr.Carpenter on this account 

 attribute its motion to gravity ? Would he attribute the motion 

 of the lower half to gravity and the upper half to the wind ? 

 He could not in consistency with his theory attribute the motion 

 of the upper half to gravity ; for although the ice-cold water ex- 

 tended to the surface, this could not explain how gravity should 

 move it southward instead of polewards, as according to theory 

 it ought to move. He might affirm, if he chose, that the sur- 

 face-water moves southwards because it is dragged forward by the 

 bottom-water ; but if this view be held, he is not entitled to 



* Dr. Carpenter " On the Gulf-stream," Proc. of Roy. Geog. Soc. for 

 January 9, 1871, § 29. 



