226 HISTORY OF PHYSICAL ASTRONOMY. 



disturbing power depends. Thus, in 1813, Lindenau 

 published Tables of Mercury, and concluded, from 

 them, that a considerable increase of the supposed 

 mass of Venus was necessary to reconcile theory 

 with observation 21 . He had published Tables of 

 Venus in 1810, and of Mars in 1811. And, in 

 proving Bouvard's Tables of Jupiter and Saturn, 

 values were obtained of the masses of those planets. 

 The form in which the question of the truth of the 

 doctrine of universal gravitation now offers itself to 

 the minds of astronomers, is this : that it is taken 

 for granted that it will account for the motions of 

 the heavenly bodies, and the question is, with what 

 supposed masses it will give the best account 82 . The 

 continually-increasing accuracy of the table shows 

 the truth of the fundamental assumption. 



The question of perturbation is exemplified in 

 the satellites also. Thus the satellites of Jupiter 

 are not only disturbed by the sun, as the moon is, 

 but also by each other, as the planets are. This 



21 Airy. Report on Ast. to Brit. Ass. 1832. 



22 Among the most important corrections of the supposed 

 masses of the planets, we ,may notice that of Jupiter, by Pro- 

 fessor Airy. This determination of Jupiter's mass was founded, 

 not on the effect as seen in perturbations, but on a much more 

 direct datum, the time of revolution of his fourth satellite. It 

 appeared, from this calculation, that Jupiter's mass required to 

 be increased by about l-80th. This result agrees with that 

 which has been derived by German astronomers from the per- 

 turbations which the attractions of Jupiter produces in the four 

 new planets, and has been generally adopted as an improvement 

 of the elements of our system. 



