182 OUTLINES OF NATURAL PHILOSOPHY. 



credible labour, a complete theory of their mo- 

 tions has been established. 



181. The time from the middle of one eclipse 

 of a satellite, to the middle of the next, is the 

 time of its synodic revolution, and is equal to 

 the time of its revolution round Jupiter, in- 

 creased by the time which it takes to describe 

 an arch of its orbit, equal to the arch which 

 Jupiter has described in the same time round 



the Sun. 



., 



a. The synodic revolution of a satellite is subject to 

 variation, as the rate of Jupiter's motion, in his or- 

 bit, is not-uniform. The greatest equation of Ju- 

 piter's orbit is 11 8' .2"; and the time of the first 

 satellite's moving over an arch equal to this, is 

 39m 22 s ; and so much, therefore, may the syno- 

 dic revolutions of that satellite differ from the 

 mean. Those of the 4th may differ 6h 13m from 

 the same cause. VINCE, Astron. vol. I. 4-19. LA 



LANDE, Astron. 2925. 







' 



182. The synodical revolutions of the same 



satellite, are subject to an inequality, depend- 

 ing on the distance of the Earth from Jupiter. 



a. When the Earth is nearest to Jupiter, or at the 

 time of Jupiter's opposition to the Sun, if the sy- 

 nodic revolution be n, the successive eclipses 

 should happen at the intervals n, 2 , 3 n, &c. 



reckoning 





