Chap. IH.] INERTION. 49 



Therefore the action of vis-inertice must tend to 

 circulate the water by a stream running through the 

 deep and central parts of the ocean in the opposite 

 direction to that of the earth's motion, and along the 

 shores in the direction of the earth's motion. 



But as regards the action of vis-inertice resulting 

 from the axial rotation of the earth, not only is there 

 this difference in the eflfective force acting in dif- 

 ferent parts of the ocean, proportioned to the relative 

 freedom from friction; but also, besides this, the 

 actual velocity of the motion is not the same in all 

 parts of the ocean, but is greater at the equator, de- 

 creasing gradually towards the poles ; and is greater 

 at the surface, decreasing gradually towards the 

 bottom of the ocean : and therefore, the actual action 

 of vis -inertias is greater in equatorial than in polar 

 regions, and greater in the upper than the lower 

 strata of water, in proportion with the difference in 

 the velocity of the motion of axial rotation in dif- 

 ferent latitudes, and at different depths of the ocean. 

 And thus, therefore, notwithstanding that the velocity 

 of the orbital motion of the earth, as also probably 

 that of the motion of the solar system, is far greater 

 than the velocity of the motion of axial rotation at 

 any part of the earth's surface, by the latter motion 

 a far greater amount of force effective in causing 

 ocean currents may — indeed almost obviously must 

 — be brought into play than can be brought into 

 play by the orbital motion of the earth, or by any 



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