PHYSICAL ASTRONOMY. #79 



277- Uranus y on account of his great dis- 

 tance, suffers no disturbance in his motion but 

 from Saturn and Jupiter. The principal ine- 

 quality depends on Saturn ; which, if S be the 

 longitude of that planet, U of Uranus, and A of 

 the aphelion of Saturn, is .30" sin(S 2U+ A). 



For the other equations, see LA LANDE, Astron. in. 

 3671. Also the New Tables^ VINCE, Astron. in. 

 p. 106. 



The orbit of Uranus is also disturbed. The node 

 moves backward at the rate 34>",25 annually, and 

 the aphelion forward at that of 2".55. The ec- 

 centricity increases, and the secular variation of 

 the greatest equation of the centre is + 11 ".03. 



When, in the preceding Tables, a planet is repre- 

 sented as producing a change in the place of its 

 node, it must be understood that it does not pro- 

 duce this effect by its action on its own orbit, but 

 by its action on the plane of the ecliptic. 



278. Comets, in describing their elliptic orbits 

 round the Sun, have been found to be disturb- 

 ed by the action of the larger planets, Jupi- 

 ter and Saturn ; but the great eccentricity of 

 their orbits, makes it impossible, in the present 

 state of mathematical science, to assign the 

 quantity of that disturbance for an indefinite 

 number of revolutions, though it may be done 



for 



