PHYSICAL ASTRONOMY. 287 



Observation alone led M. WARGENTIN to the know- 

 ledge of these inequalities, but he could not dis- 

 cover the law. 



287. The orbit of the fourth satellite moves 

 on a fixed plane, to which it is inclined at an 

 angle of 14/ 58", and its nodes complete a side- 

 rial revolution (backward) in 531 years- The 

 fixed plane itself is inclined at an angle of 

 24' 33" to the equator of Jupiter ; the orbit is 

 very sensibly elliptical, and the line of the ap- 

 sides has an annual motion of 43'34".7 



The motion of the apsides of this satellite is one- of 

 the principal data from which the quantities of 

 matter have been determined. 



288. If the mass of Jupiter be supposed uni- 

 ty, the mass of the 1st Sat. = .0000173281 



of the 2d = .0000232355 



of the 3d = .0000884972 



of the 4th = .0000426591 



If the mass of the Earth be put = 1, that of the 

 third satellite will be found .027337. Now the mass 



of the Moon is = .OU599, and therefore the 



DO. 5 



quantity of matter in the third satellite is about 

 twice as great as that in the Moon. The fourth 



satellite 



