478 Royal Astronomical Society. 



2 h 36 m the suspected satellite had moved westward 2 S, 46, and that 

 in l h 24 m Japetus (the identification of which was now certain) had 

 also moved westward 1 8, 27. It is true that these differences are 

 somewhat greater than is consistent with the orbital motion of Saturn, 

 yet perhaps not greater than is consistent with reasonable errors of 

 observation during so short a period. Moreover, as the suspected new 

 satellite was situated precisely in the line of the satellites interior to 

 itself, I took micrometrical measurements of its situation at two 

 epochs, four hours apart, and was satisfied that during that interval 

 no perceptible change whatever took place in its position in the line 

 of the satellites. As the motion of Saturn southwards in the same 

 period amounted to 18", he must have left the suspected satellite 

 obviously behind if it had been a fixed star. I could therefore now 

 arrive at no other conclusion than that I had discovered a satellite 

 hitherto undetected. 



" I regret that since the 19th of September the weather has been 

 remarkably unfavourable. I obtained a good set of measures of the 

 elongation of the satellite on the 21st, and two very hasty measures 

 on the 22nd, caught between clouds, which, with an estimation of 

 its elongation on the 18th, are all the data I have hitherto obtained 

 towards the determination of its period. Since the latter date the 

 weather has been uniformly cloudy. 



• " If these observations should be thought worthy of being recorded 

 until better can be obtained, they would stand thus : — 



Sept. 18, Elongation east of Saturn (estimated by ) i fa 

 comparison with Titan) J 



21, Elongation, measured 3 54 



22, Ditto ditto 3 27 



" These observations would, I believe, be best satisfied by a period 

 of about twenty -four days, which may at least serve as a guide in 

 looking for the satellite. Its magnitude is very small, perhaps not 

 intrinsically so great as that of Mimas, though it was much easier 

 to see, on account of its greater distance from the planet. 



" During this autumn I have twice been gratified with a sight of 

 the whole seven satellites of Saturn at one time, viz. on the 19th of 

 August and on the 16th of September, at ll h 15 m . The observa- 

 tions of the latter evening were very interesting. I first saw the 

 planet a little before 10 h , when Tethys was behind the planet, and 

 Enceladus and Dione absolutely in one. I immediately recognized 

 Mimas, and in a veiy short time Enceladus emerged from conjunction 

 with Dione, and then appeared with the latter as the most delicate 

 double-star possible. At 1 l h 30 m Titan had approached close up to 

 the ball, and was apparently in contact with it. At 1 l h 35 m it had 

 become occulted. At 1 l h 5 m I observed Tethys just emerging from 

 behind the ball, and noticed that he emerged evidently south of the 

 line joining the other satellites. As the present position of the ring 

 requires that, if revolving in its plane, the satellite should appear 

 rather to the north on its emergence, this fact seems to afford some 

 evidence that the satellite does not revolve precisely in the plane of 

 the ring. Moreover, at ll h 50 m , when Tethys and Mimas formed 



