310 LAPLACE. 



This rank, which was lost for a moment, was bril- 

 liantly regained, an achievement for which we are in- 

 debted to four geometers. 



When Newton, giving to his discoveries a generality 

 which the laws of Kepler did not imply, imagined that 

 the different planets were not only attracted by the sun, 

 but that they also attract each other, he introduced into 

 the heavens a cause of universal disturbance. Astrono- 

 mers could then see at the first glance that in no part of 

 the universe whether near or distant would the Kep- 

 lerian laws suffice for the exact representation of the 

 phenomena; that the simple, regular movements with 

 which the imaginations of the ancients were pleased to 

 endue the heavenly bodies would experience numerous, 

 considerable, perpetually changing perturbations. 



To discover several of these perturbations, to assign 

 their nature, and in a few rare cases their numerical 

 values, such was the object which Newton proposed to 

 himself in writing the Principia Mathematica Philo- 

 sophice Naturalis. 



with a similar arc measured in Lapland, from which it appeared that 

 the length of a degree of the meridian increases from the equator 

 towards the poles, conformably to what ought to result upon the sup- 

 position of the earth having the figure of an oblate spheroid. The 

 length of the Lapland arc was determined by means of an expedition 

 which the French Government had despatched to the North of Europe 

 for that purpose. A similar expedition had been despatched from 

 France about the same time to Peru in South America, for the pur- 

 pose of measuring an arc of the meridian under the equator, but the 

 results had not been ascertained at the time to which the author 

 alludes in the text. The variation of gravity at the surface of the 

 earth was established by Kicher's experiments with the pendulum at 

 Cayenne, in South America (1673-4), from which it appeared that the 

 pendulum oscillates more slowly and consequently the force of grav- 

 ity is less intense under the equator than in the latitude of Paris. 

 Translator. 



