SEQUEL TO THE EPOCH OF NEWTON. 223 



Sect. 3. Application of the Newtonian Theory to 

 the Planets, Satellites, and Earth. 



THE theories of the Planets and Satellites, as af- 

 fected by the law of universal gravitation, and 

 therefore by perturbations, were naturally subjects 

 of interest, after the promulgation of that law. 

 Some of the effects of the mutual attraction of the 

 planets had, indeed, already attracted notice. The 

 inequality produced by the mutual attraction of 

 Jupiter and Saturn cannot be overlooked by a good 

 observer. In the preface to the second edition of 

 the Principia, Cotes remarks 17 , that the perturba- 

 tion of Jupiter and Saturn is not unknown to astro- 

 nomers. In Halley's Tables it was noticed 18 that 

 there are very great deviations from regularity in 

 these two planets, and these deviations are ascribed 

 to the perturbing force of the planets on each other; 

 but the correction of these by a suitable equation is 

 left to succeeding astronomers. 



The motion of the planes and apsides of the 

 planetary orbits was one of the first results of their 

 mutual perturbation which was observed. In 1706, 

 La Hire and Maraldi compared Jupiter with the 

 Rudolphine Tables, and those of Bullialdus ; it ap- 

 peared that his aphelion had advanced, and that his 

 nodes had regressed. In 1728, J. Cassini found that 

 Saturn's aphelion had in like manner travelled for- 



17 Preface to Principia, p. xxi. 



18 End of Planetary Tables. 



