Wind and Gravitation Theories of Oceanic Circulation. 249 



perature of the North Pacific is that the surface-flow in that 

 ocean is reversed, and that, instead of flowing, as everywhere 

 else, from a lower to a higher latitude, it flows in the opposite 

 direction. His theory is that there is an underflow from the 

 Antarctic regions northwards across the equator up to about 

 latitude 52° N., and a counter surface-flow from that latitude 

 southwards across the equator to the Antarctic regions. And 

 he gives a diagram illustrating this mode of circulation. But 

 it must be perfectly obvious that no such flow could be produced, 

 according to the gravitation theory, from difference of tempera- 

 ture. The difference of temperature, which is the prime mover 

 according to this theory, results from the difference in the amount 

 of heat received from the sun at equatorial and polar regions. 

 The sea is warmer in equatorial than in temperate regions, 

 because the amount of heat received from the sun is greater in 

 the former than in the latter regions ; and for the same reason the 

 sea in temperate is warmer than in polar regions. It is therefore 

 impossible, according to the gravitation theory, that the ocean at 

 latitude 52° can be warmer than at the equator. But, unless it 

 were so, there could be no surface-flow due to gravitation from lat- 

 itude 52° to the equator^ because the surface of the ocean would 

 not be higher in that latitude than at the equator, and without a 

 slope gravitation could not act, I, of course, admit that the 

 ocean may actually be warmer in temperate than in polar regions ; 

 for of this we have, as already shown, a good example in the 

 case of the North Atlantic ; but then no such condition of things 

 could arise from a circulation resulting from difference of tem- 

 perature. A swf ace-flow from temperate regions across the equator, 

 sustained by difference of temperature, is simply a mechanical im- 

 possibility. 



The truth is, that the adoption of such a mode of circulation 

 makes the gravitation theory self- contradictory ; for, according 

 to that theory, it is the lowness of the temperature of the ocean in 

 high latitudes, in comparison with that in low, which is the reason 

 why the surface-flew is toward the poles ; but in the case of the 

 North Pacific this low temperature in high latitudes is adduced 

 as a reason why the flow is in the reverse direction, viz. towards 

 the equator. 



According to the wind theory the explanation of the pheno- 

 mena is plain and obvious. The North Pacific is colder than 

 the North Atlantic, because, although much larger, it neverthe- 

 less receives less heat from ocean-currents than the North 

 Atlantic. It is warmer at lat. 52° than at lat. 43°, because the 

 former place lies more in the path of a warm current than the 

 latter. 



The Southern Ocean. — The thermal condition of the Southern 



