114 THE OCEAN. [Book IV. 



fleeted by the coast-lines, the undulations must never- 

 theless be under the dominion of the forces there de- 

 scribed : according to which, as the luni- solar forces 

 move westwards in relation to the surface of the earth, 

 they carry the tides westwards with them in the equa- 

 torial regions, in which the force of their attraction 

 is greatest ; whilst, at the same time, the force of 

 terrestrial gravitation maintains the equilibrium of 

 the ocean on the surface of the earth by drawing an 

 exactly equal mass of the tide eastwards through the 

 temperate zones, in which the ocean is more under 

 the dominion of the earth's gravitation, and less 

 under the dominion of the forces which raise the 

 luni-solar tides, than in the equatorial regions. And 

 thus, therefore, the relative volume of water on 

 every meridian, and on every parallel, can never 

 vary. 



The position of the ocean in relation to the surface 

 of the earth is determined by universal gravitation or 

 vis-inertiae, and is constantly the same both in longi- 

 tude and latitude. Though the luni-solar forces change 

 their positions in relation to the surface of the earth, 

 the volume of water on every meridian and on every 

 parallel remains, nevertheless, constantly the same ; 

 because this is determined by the combined power of 

 the gravitation of the universe, and cannot be affected 

 by the individual action of any of the forces of gravi- 

 tation within the universe. As the luni-solar forces 

 move a volume of water from any part of any 



