LAPLACE. • 149 



with each other in order to arrive at results expressed even to the pre- 

 cision of the smallest decimals ? 



On the one hand, mathematical formulse deduced from the principle 

 of universal attraction ; on the other hand, certain irregularities ob- 

 served in the returns of the moon to the meridian. 



An observing geometer who, from his infancy, had never quitted his 

 chamber of study, and who had never viewed the heavens except 

 through a narrow aperture directed north and south, in the vertical 

 l)lane of which the i»rinci[)al astronomical instruments aremadetomove — 

 to whom nothing had ever been revealed respecting the bodies revolving 

 above his head, except that they attract each other according to the 

 Newtonian law of gravitation — would, however, be enabled to ascertain 

 that his narrow abode was situated upon the surfiice of a spheroidal 

 body, the equatorial axis of which surpassed the polar axis by a three 

 hundred and sixth part; he would have also found, in his isolated, im 

 movable ])osition, his true distance from the sun. 



I have stated at the commencement of this notice that it is to 

 D'Alembert we owe the first satisfactory mathematical explanation of 

 the phenomenon of the precession of the equinoxes. But our illustrious 

 countryman, as well as Enler,Avhose solution appeared subsequently to 

 that of D'Alembert, omitted all consideration of certain physical cir- 

 cumstances, which, however, did not seem to be of a nature to be neg- 

 lected without examination. Laplace has supplied this deficiency. He 

 has shown that the sea, notwithstanding its fluidity, and that the at- 

 mosphere, notwithstanding its currents, exercise the same influence on 

 the movements of the terrestrial axis as if they formed solid masses ad- 

 hering to the terrestrial spheroid. 



Do the extremities of the axis around which the earth performs an 

 entire revolution once in every twenty four hours correspond always to 

 the same material points of the terrestrial spheroid ? In other words, 

 do the poles of rotation, which from year to year correspond to different 

 stars, undergo also a displacement at the surface of the earth ? 



In the case of the afiirmative, the equator is movable as well as the 

 poles : the terrestrial latitudes are variable ; no country during the lapse 

 of ages will enjoy, even on an average, a constant climate; regions the 

 most ditferent will, in their turn, become circumpolar. Adopt the cor.- 

 trary supposition, and everything assumes the character of an admi- 

 rable permanence. 



The question which I have just suggested, one of the most important 

 in astronomy, cannot be solved by the aid of mere observation, on ac- 

 count of the uncertainty of the early determinations of terrestrial lati- 

 tude. Lai)lace has supplied this defect by analysis. The great geome- 

 ter lias demonstrated ihat no circumstance depending on universal gravi- 

 tation can sensibly disjAace the poles of the earth's axis relatively to 

 the surface of the terrestrial spheroid. The sea, far from being an ob- 

 stacle to the invariable rotation of the earth upon its axis, would, on the 



