THE TIDES. 165 



side up to a certain depth, and the earth would 

 be as it were floating out of the sea. That ex- 

 plains one curious result that Laplace seems to 

 have been much struck with : the stability of 

 the ocean requires that the density of the water 

 should be less than that of the solid earth. But 

 take the sea as having the specific gravity of 

 water, the mean density of the earth is only 

 5 "6 times that of water, and this is not enough 

 to prevent the attraction of water for water from 

 being sensible. Owing therefore to the attraction 

 of the water for parts of itself the tidal pheno- 

 mena are somewhat larger than they would be 

 without it, but neglecting this, and neglecting 

 the deformation of the solid earth, we have the 

 ordinary equilibrium theory. 



Why does the water not follow the equilibrium 

 theory ? Why have we tides of 20 feet or 30 

 feet or 40 feet in some places, arid only of 2 or 

 3 feet in others ? Because the water has not 

 time in the course of 12 hours to take the equi- 

 librium figure, and because after tending towards 

 it, the water runs beyond it. 



