APPENDIX. 



Position of Ariel. 



Bet. 

 & 180 



345.4 



320.1 

 1.3 



350.1 



13.96 



10.45 

 13.27 



13.89 



Hence it is plain that Lassell saw Ariel on Sept. 14, Sept. 2T, 

 and Nov. 6, and possibly on Sept. 29. Um oriel was seen on 

 Oct. 1. 



Struve's observations are given in Monthly Notices of the Royal 

 Astronomical Society, vol. viii. p. 46, as follows: — 



Hence Struve may have seen Umbriel Nov. 1 and Dec. 10, 

 1847. 



In 1871 observations of Ariel and Umbriel were made at 

 Bothkamp with a telescope of twelve inches aperture and com- 

 pared with Marth's ephemeris for that year. The positions of 

 Ariel differ from their predicted positions by a large angle, nearly 

 180^, wliile the positions of Umbriel agree well. Ariel, how- 

 ever, is much the brighter of the two inner satellites, and as it 

 evidently was not seen at all, it becomes probable that a small 

 star was mistaken for Umbriel on the five nights of observation. 



This supposition is strengthened when wo consider that the 

 Bothkamp observers found Titania and Oberon difficult objects, 

 which they certainly are not to any telescope which will show 

 Ariel or Umbriel. Lassell estimates that Oberon and Titania 

 are twice as bright intrinsically as either of the inner satellites, 

 and this estimate is probably not too high. 



We may then fairly claim that Sir WMiam Herschel saw all four 

 of the satellites of Uranus, that Lassell discovered independently 

 10 CZb) 



