348 LAPLACE. 



attentive and minute study of the oscillations of the 

 ocean. We know only one means of enhancing the 

 admiration which every thoughtful mind will entertain 

 for theories capable of leading to such conclusions. An 

 historical statement will supply it. In the year 1631, 

 the illustrious Galileo, as appears from his Dialogues, 

 was so far from perceiving the mathematical relations 

 from which Laplace deduced results so beautiful, so 

 unequivocal, and so useful, that he taxed with frivolous- 

 ness the vague idea which Kepler entertained of attribut- 

 ino- to the moon's attraction a certain share in the pro- 



o 



duction of the diurnal and periodical movements of the 

 waters of the ocean. 



Laplace did not confine himself to extending so con- 

 siderably, and improving so essentially, the mathematical 

 theory of the tides ; he considered the phenomenon from 

 an entirely new point of view ; it was he who first 

 treated of the stability of the ocean. Systems of bodies, 

 whether solid or fluid, are subject to two kinds of equi- 

 librium, which we must carefully distinguish from each 

 other. In the case of stable equilibrium the system, 

 when slightly disturbed, tends always to return to its 

 original condition. On the other hand, when the system 

 is in unstable equilibrium, a very insignificant derange- 

 ment might occasion an enormous dislocation in the 

 relative positions of its constituent parts. 



If the equilibrium of waves is of the latter kind, the 

 waves engendered by the action of winds, by earth- 

 quakes, and by sudden movements from the bottom of 

 the ocean, have perhaps risen in past times and may rise 

 in the future to the height of the highest mountains. 

 The geologist will have the satisfaction of deducing from 

 these prodigious oscillations a rational explanation of a 



