LAPLACE. 143 



into iiDkuown regious, whitber the eye^ armed v.ith the most powerful 

 telescope, has uever penetrated. Jupiter, on the other haud, the pkiuet 

 compared with which the earth is so insiguificant, appeared to be mov- 

 ing ill the opposite direction, so as to be ultimately absorbed in the in- 

 candescent matter of the sun. Finally, the moon seemed as if it would 

 one day precipitate itself upon the earth. 



There was nothing doubtful or speculative in these sinister fore- 

 bodings. The precise dates of the approaching catastrophes were alone 

 uncertain. It was known, however, that they were very distant. Ac- 

 cordingly, neither the learned dissertations of men of science nor the 

 animated descriptions of certain poets produced any imijression upon the 

 public mind. 



It was not so with our scientific societies, the members of which re- 

 garded with regret the approaching desiruction of our planetary system. 

 The Academy of Sciences called the attention of geometers of all coun- 

 tries to these menacing perturbations. Euler and Lagrange descended 

 into the arena. Never did their mathematical genius shine with a 

 brighter luster. Still the question remained undecided. The inutility of 

 such eflbrts seemed to suggest only a feeling of resignation on the sub- 

 ject, when from two disdained corners of the theories of analysis the 

 author of the Mecanique Celeste caused the laws of these great phenom- 

 ena clearly to emerge. The variations of velocity of Jupiter, Saturn, 

 and the moon flowed, then, from evident physical causes, and entered 

 into the category of ordinary periodic perturbations, depending upon 

 the principle of attraction. 



The variations in the dimensions of the orbits, which were so much 

 dreaded, resolved themselves into simple oscillations, included within 

 narrow limits. Finally, by the powerful instrumentality of mathemati- 

 cal analysis, the physical universe was again established on a firm foun- 

 dation, 



I cannot quit this subject without at least alluding to the circumstances 

 in the solar system upon which depend the so long unexplained varia- 

 tions of velocity of the moon, Jupiter, and Saturn. 



The motion of the earth around the sun is mainl}^ effected in an ellipse, 

 the form of which is liable to vary from the effects of planetary pertur- 

 bation. These alterations of form are periodic ; sometimes the curve, 

 without ceasing to be eliiptic, approaches the form of a circle, while at 

 other times it deviates more and more from that form. From the epoch 

 of the earliest recorded observations, the eccentricity of the terrestrial 

 orbit has been diminishing from year to year ; at some future epoch the 

 orbit, on the contrary, will begin to deviate i'rom the form of a circle, and 

 the eccentricity will increase to the same extent as it previously dimin- 

 ished, and according to the same laws. 



Now Laplace has shown that the mean motion of the moon around 

 the earth is connected with the form of the ellipse which the earth de- 



