Royal Astronomical Society. 239 



That the satellite a should never have been seen by M. O. Struve 

 may arise from its becoming faint in the southern portion of its 

 orbit, as c probably does in the northern. It appears, from calcula- 

 tion on the assumptions before mentioned, that on every night when 

 M. O. Struve saw c, with the only exception of Dec. 10, a was in 

 the southern portion of its orbit ; yet sufficiently distant from his 

 observed position of c to render any confusion between them impos- 

 sible. On Nov. 28, indeed, the position-angles of the two satellites 

 must have been almost precisely the same : but the measured distance 

 of c was 16" - 85 ; while the distance of a could not have exceeded 

 11" in that part of its orbit. It should be noticed, with reference 

 to the non-observation at Poulkova of the satellite a on Dec. 10, that 

 though on that night near its greatest northern elongation, it was at 

 a smaller distance from the primary than c ever was when it was 

 observed. Unless, therefore, the night were unusually fine, so faint 

 an object might easily be overlooked. 



So long ago as the autumn of 1845, Mr. Lassell occasionally saw 

 a faint object, supposed to be a satellite, at about the same distance 

 from the planet as a was observed to have been last year; and, with 

 only one exception, it was always seen on the northern side of the 

 primary, and usually in the north preceding quadrant, in which it 

 was uniformly seen in 1847. On Oct. 5, 1845, at 12 h 26 m Green- 

 wich mean time, being on a visit at Starfield, I had the gratification 

 of seeing this satellite in the 20-foot reflector. When the light of 

 the planet was hidden from the eye by a bar, the satellite became 

 steadily visible ; and a careful diagram being made, both by Mr. 

 Lassell and myself independently, the position-angles deduced from, 

 them agreed within 3°, the mean being 324°-l. This is very nearly 

 the same with the estimated position on Sept. 27, 1847 ; and assu- 

 ming, that in the interval of 721 -8896 days, 342 complete revolutions 

 had been performed, the period comes out 2 d 2 h 39 m 36 s . It seems 

 probable, therefore, that the period of this satellite does not differ 

 much from that quantity. 



Supposing that those nights on which the satellites I. and II. were 

 measured at Starfield in J 847 were probably favourable, though a 

 was not noticed, it becomes interesting to know whether a were 

 then at such a distance from the planet as might allow it to be visible 

 in the 20-foot reflector. I have therefore computed the places of a 

 for each of those nights ; and the results show, that only on Oct. 1 6 

 was it in the northern portion of its orbit, and not very close to its 

 primary. On every other occasion, therefore, it was probably either 

 invisible in the southern portion of its orbit, or overpowered by its 

 vicinity to the planet. 



By a similar computation, it becomes evident, that on none of 

 those nights was the satellite c near its greatest southern elongation; 

 and that, therefore, it was probably invisible on the northern side of 

 the planet, or too near it to be discerned. 



It is singular, that in the whole series of observations at Starfield 

 and Poulkova, only one night, Nov. 1, is common to them both ; 

 nd that was of so indifferent a quality at Starfield, as to render it 



