PHYSICAL ASTRONOMY. 323 



p. 284?. Also, that the changes in the inclinations 

 of the planetary orbits, are all periodical, and can- 

 not carry the planes of those orbits .beyond the li- 

 mits of the zodiac, or 8 on either side of the 

 ecliptic. By the retrogradations of the nodes of 

 the ecliptic and the planetary orbits, the preces- 

 sion of the equinoxes is diminished by a small 

 quantity, which is at present about 0".261 annual- 

 ly. Ibid. p. 28 1 . All this is quite independent 

 of the figure of the Earth, and would be the same 

 though the Earth were truly spherical. 



THE first solution of the problem of the Precession 

 was given by NEWTON, Princip. lib. in. prop. 39. 

 It is not free from error; but it displays, in a 

 strong light, the resources of genius contending 

 with the imperfections of a science not sufficiently 

 advanced for so arduous an investigation. One 

 mistake has already been pointed out, $318; ano- 

 ther consisted in supposing, that the motion of 

 the nodes of the Ring surrounding the equator, 

 must be the same with those of the Moon, allow- 

 ing for the different time of rotation, and the dif- 

 ferent inclination to the ecliptic. 



D'ALEMBERT corrected these mistakes, and gave an 

 accurate, though prolix solution, which also compre- 

 hended in it the theory of the Nutation. Precession 



des 



