OUTLINES OF NATURAL PHILOSOPHY. 



a. Of the motion of the apsides, 5" is due to Venus, 

 1".2 to Mars, and 5". ,5 to Jupiter nearly. 



b. In the secular diminution of the equation to the 

 centre, + 4/'.l 8 is the effect of Venus, - 4/'.94< of 

 Mars, 16".02 of Jupiter, and the rest is produ- 

 ced by Mercury and Saturn. 



. As it is not the centre of the Earth, but 

 the centre of gravity of the Moon and Earth, 

 which describes equal areas, in equal times, 

 about the centre of the Sun, the regularity of 

 the Earth's motion is disturbed on that account, 

 and the Earth is forced out of the plane of the 

 ecliptic. 



a. The irregularities thus communicated to the Earth 

 are, by observers on its surface, transferred to the 

 Sun ; the Sun, therefore, has a motion in longi- 

 tude, by which he alternately advances before the 

 point that describes the elliptical orbit in the hea- 

 vens, and falls behind it ; and in like manner al- 

 ternately ascends above the plane of the ecliptic, 

 and descends below it. 



b. These inequalities are small. The mass of the 

 Moon is about ^th of that of the Earth ; the 

 distance, therefore, of the centre of gravity of the 

 Moon and Earth, from the centre of the latter, 

 must be less than a semidiameter, and therefore 

 the inequality in the Sun's place must be less 

 than his horizontal parallax. 



c. The 



