6. 



THE MASS OF URANUS. 

 [From the Monthly Notices of the Royal Astronomical Society. Vol. ix. (1849.)] 



THE mass of Uranus is a very important element in the determination 

 of the orbit of Neptune. Two values of this mass have been given, differing 

 widely from each other. Bouvard, from the action of Uranus on Saturn, 



found the mass to be ry^s' tnat of the sun bein g =1; while more re " 

 cently, from observations of the satellites, Lamont has obtained the value 

 zzfoj. In order to throw light on this subject, Mr Lassell was kind enough 

 to make for me the observations of the satellites of Uranus, which are 

 given in the Monthly Notice for March last. 



These I have carefully reduced, and the value of the mass which I 

 have found from the observations of the fourth satellite (which are more 

 to be depended on for this purpose than those of the second) is 2 oia7 > 

 which is almost exactly a mean between the results of Bouvard and 

 Lamont. In obtaining this result, I have rejected the first day's observa- 

 tions, which are discordant both for the second and fourth satellites. 



I have also reduced all Sir Wm. Herschel's measures of distance of 

 the satellites given in his paper in the Phil. Trans., 1815, and the value 

 of the mass obtained from the observations of the fourth satellite is 21^65 

 which agrees very closely with that found from Mr Lassell's observations. 

 Although, therefore, more numerous observations will be requisite in order 

 to obtain a mass which may be used with confidence in the theory of 

 Neptune, I have no doubt that the value 21000 ' IS mu ch nearer the truth 

 than either of those which have been previously given, and I shall ac- 

 cordingly employ it in my subsequent calculations respecting the orbit of 

 Neptune. 



The most probable values of the periods of the second and fourth 

 satellites, given by the combination of the observations of Sir Wm. Herschel, 

 Sir J. Herschel, Lamont, and Mr Lassell, are 8 d 7058435 and 13 d> 463139 

 respectively ; but the remaining errors of the epochs are greater than can 

 with probability be ascribed to mere errors of observation, and seem to 

 indicate the existence of considerable perturbations. 



