66 Royal Astronomical Society. 



and its decomposition by heat by the equation 



Cios Hjos 4 = C 54 H 54 4 + C 54 H54, 

 the substance itself belonging to the class of compound ethers. 



The author announces his intention of following up this paper by 

 a third on the constitution of myricine. 



ROYAL ASTRONOMICAL SOCIETY. 



[Continued from vol. xxxii. p. 148.] 



Jan. 14, 1848. — Satellites of Saturn. 



Observations of Mimas, the closest and most interior satellite of 

 Saturn. By Mr. Lassell. 



It is to be regretted that, owing to the discovery of the closest 

 two satellites of Saturn having been made at a period long after the 

 five others became known, it is difficult, in referring to the indivi- 

 duals, to quote them by numerals which shall, explicitly and without 

 ambiguity, point out which satellites are meant. 



Sir John Herschel, seeing this difficulty, has invented and pub- 

 lished in his Cape Observations a nomenclature which completely 

 removes it, and moreover will retain its precision should any more 

 satellites hereafter be discovered. He gives a proper name to each 

 of them ; and beginning with that nearest to Saturn, designates 

 them thus : Mimas, Enceladus, Tethys, Dione Rhea, Titan, and 

 Japetus. I cannot but think this nomenclature a great improve- 

 ment, and worthy of general adoption. 



Of Mimas, the satellite I now refer to, I have obtained in all five 

 observations. 



1846, Aug. 25. About 11^ p.m. mean time the satellite appeared 

 at its greatest elongation westward. Aug. 30. The satellite appeared 

 a little short of its greatest elongation eastward ; and again, on the 

 1st of September at 10 p.m., the satellite appeared a little beyond 

 its greatest eastern elongation. 



During the late opposition of Saturn, although I have been very 

 watchful of opportunities, I have been able to see it certainly but 

 twice, viz. on the 16th of October and 18th of November. 



On the 16th of October at 8 h 35 m mean time, Mimas was, as 

 nearly as I could estimate, exactly at its greatest western elongation, 

 appearing to be five or six-tenths of the length of the preceding arm 

 of the ring distant from its extremity. This evening the satellite 

 was better seen than on any other occasion. 



On the 18th of November, at about 8^ hours, the satellite again 

 appeared as nearly as possible in the same situation as on the 1 6th 

 of October. The power with which Mimas was generally best seen 

 is a Coddington lens magnifying 567 times. The difference of visi- 

 bility between Mimas and Enceladus is almost incomparable ; the 

 latter being instantly seen in my telescope, under all tolerable cir- 

 cumstances, when within 40° or 50° of its greatest elongation ; whilst 

 in any but the very finest circumstances, Mimas is an object of great 

 difficulty. 



