LAPLACE. 155 



Laplace did not confine himself to extending so considerably, and im- 

 proving so essentially, the matheauitical theory of the tides ; he consid- 

 ered 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 equilibrium, which we must 

 carefully distinguish from each other. In the case of stable equilibrium, 

 the systeuij when slightly disturbed, tends always to return to its origi- 

 nal condition. On the other hand, when the system is in unstable e(iuilib- 

 rium, a very iusigniticaut derangement might occasion an enormous 

 dislocation in the relative i)ositions of its constituent parts. 



If the equlibrium of waves is of the latter kind, the waves engendered 

 by the action of winds, by earthquakes, and by sudden movements 

 from the bottom of the ocean, have perhaps risen in i)ast times, and 

 may rise in the luture, to the height of the highest mountains. The 

 geologist will have the satisfaction of deducing i'rom these prodigious 

 oscillations a rational explanation of a great multitude of phenomena, 

 but the public will thereby be exi)osed to new and terrible catastro- 

 phes. 



Mankind may rest assured ; Lapkice has proved, that the equilibrium 

 of the ocean is stable, but ujjon the express condition (which, however, 

 has been amply verified by established facts) that the mean density of 

 the fluid mass is less than the mean density of the earth. Everything 

 else remaining the same, let us substitute an ocean of mercury for the 

 actual ocean, and the stability will disappear, and the flui<l will fre- 

 quently surpass its boundaries, to ravage continents even to the height 

 of the snowy regions which lose themselves in the clouds. 



Does not the reader remark how each of the analytical investigations 

 of Laplace serves to disclose the harmony and duration of the universe 

 and of our globe I 



Jt was imi)ossible that the great geometer, who had succeeded so 

 well in the study of the tides of the ocean, should not have occupied 

 his attention with the tides of the atmosphere ; that he should not have 

 submitted to the delicate and definitive tests of a rigorous calculus the 

 generally-ditlused opinions respecting the influence of the moon upon the 

 height of the barometer and other meteorological phendmena. 



Laplace, in effect, has devoted a chapter of his splendid work to an 

 examination of the oscillations which the attractive force of the moou 

 is capable ot producing in our atmosphere. It results from these re- 

 searches that, at Paris, the lunar tide produces no sensible effect upou 

 the barometer. The height of the tide, obtained by the discus.sion of a 

 long series of observations, has not exceeded two hundredths of a n)illi- 

 meter, a quantity which, in the present state of meteorological science, 

 is less than the probable error of observation. 



The calculation to which I have just alluded may be cited in support 

 of considerations to which I had recourse when I wished to establish, 

 that if the moou alters more or less the height of the barometer, accord- 

 ing to its different phases, the effect is not attributable to attraction. 



