80 



4. Dr Traill then gave the following Notice of some of the 

 recent Astronomical Discoveries of Mr Lassell, and exhibited 

 an accurate lithograph by him of Saturn, with the re- 

 cently-detected Dark Ring, &c. &c. 



Mr William Lassell, of Starfield, near Liverpool, who has gained 

 a high reputation by his admirable method of constructing large re- 

 flecting telescopes, has largely added to his scientific character within 

 the present year (1851), by the discovery of an eighth satellite to 

 Saturn, and determining its period of revolution ; and also, by the 

 detection of two new satellites of Uranus. This last discovery is 

 thus announced by him in a letter in my possession : — 



" I have discovered two new satellites of Uranus. They are in- 

 terior to the innermost of the two bright satellites discovered by Sir 

 William Herschel, and generally known as the second and fourth. 

 It would appear, that they are also interior to Sir William Her- 

 schel's first satellite, to which he assigns a period of revolution of 

 about five days and twenty-one hours — (but which satellite I have 

 as yet been unable to recognise.) 



" I first saw these two, of which I now communicate the discovery, 

 on the 24th of October, and had then little doubt that they would 

 prove satellites. I obtained further observations of them on the 28th 

 and 30th of October, and also last night ; and find, that for so short 

 an interval, the observations are well satisfied by a period of revolu- 

 tion of almost exactly four days for the outermost, and two and a 

 half days for the closest. They are very faint objects — certainly 

 have not the brightness of the two conspicuous ones, but all four 

 were, last night, steadily visible, in the quieter moments of the air, 

 with a magnifying power of 778 on my 20 feet reflector." — Novem- 

 ber 3, 1851. 



It is well known, that the noble instrument here alluded to is the 

 work of the hands of this eminent astronomer. Its focal distance is 

 20 feet. The great mirror is 2 feet in diameter, 2j% inches in 

 thickness, and weighs 420 lb. Mr Lassell's method of obviating the 

 flexure of the mirror by its own weight, when I'esting on its edge, 

 is exceedingly ingenious. A series of twenty-seven screws, arranged 

 in triplets in thi*ee-armed iron plates, thus .*., press against the back 

 of the mirror, so as to keep its true figure unchanged by position. 

 Nothing can exceed the perfection of the metallic composition, and 



