57 



CHAPTER IV. 



GRAVITATION AND VIS-INERTIA ARE CONVERTIBLE 

 TERMS AS FAR AS THE MOVEMENTS OF THE OCEAN 

 ARE CONCERNED. 



Let us now proceed to consider wliat the forces 

 whose action we have described are in their abstract 

 nature, and what relation they bear to the forces 

 which cause the tides. 



According to Kepler's first law of gravitation, 

 enforced by Newton's demonstrations, the force of at- 

 traction proceeding from any body in space decreases 

 in proportion as the square of the distance from which 

 it acts increases ; and if this be so, then, since the 

 superficies of spheres increase in proportion as the 

 squares of their radii increase, therefore, the force of 

 attraction proceeding fi-om any centre of gravitation 

 must be exactly equal in the superficies of all spheres 

 described from that centre of gravitation ; and, 

 therefore, though the relative force of that attraction, 

 as regards other forces of attraction, must decrease 

 with an increase of distance from the centre from 

 which it proceeds, and a decrease of distance from 

 other centres of attraction, and the individuality 

 of its effects be overwhelmed by being rendered 



