Royal Astronomical Society. 67 



Satellites of Uranus*. 



Observations by Mr. Lassell. 



These observations are principally of the two brightest, those first 

 observed by Sir W. Herschel, or I. and II., with estimations of two 

 others, presumed to be his inferior and middle satellites, or 1 and 2. 

 I have not been able to obtain an undoubted observation of any sa- 

 tellite exterior to II. 



The observations are made in position and distance, like those of 

 a double star. The positions are reckoned from the north point, as 

 zero, round by the following side. 



The results here presented are generally the means of two or three 

 measures. The observations of the I. and II., graphically projected, 

 show apparently elliptic orbits, having their transverse axes very 

 nearly perpendicular to the plane of the ecliptic and the proportions 

 of the axes, roughly as 10 to 6. 



The results marked e are careful estimations only. 



As to the single observation of the satellite 2, there was unques- 

 tionably a point of light at the place indicated, which kept its rela- 

 tive position to the planet for about two hours. Moreover, that part 

 of the sky in which Uranus was seen on November 6 was carefully 

 scrutinized on November 8, without my being able to detect any 

 stars in the places where the four satellites had been seen. 



Note on the Satellites of Uranus. By M. Otto Struve. 



The satellites of Uranus were first seen by Sir W. Herschel on 

 January 11, 1787, six years after his discovery of the primary planet. 

 By a continued series of observations that year he established the 

 undoubted existence and the approximate distance and periodic times 

 of two principal satellites. In a second memoir (Phil. Trans. 1798) 

 he announced the discovery of four new supplementary satellites ; 

 and in a third memoir (Phil. Trans., 1815) he presented the results 

 of his observations to that date. The faintness of the objects ob- 



• As a temporary nomenclature, we call the two first discovered satel- 

 lites I. and II., and the others 1, 2, 3, 4, reckoning from the planet. 



F2 



