62 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



(284.) MR LASSELL. New Secondary Planets. Mr Las- 

 New Se- se n o f Liverpool deserves a more lengthened no- 

 PlanetT ^ ce ^ an our limits will permit, not only as a dis- 

 Mr Lassell. tinguished discoverer, but as one whose success can- 

 not be too widely made known as an encouragement 

 to others. This gentleman, engaged in mercantile 

 pursuits in an eminently commercial town, possessing 

 little leisure and no enormous fortune, has contrived, 

 in the intervals of business, to construct with his own 

 hands telescopes which in accuracy of definition ap- 

 pear to rival any which art stimulated by national 

 liberality has yet constructed elsewhere, and to use 

 them with a degree of skill and success which has 

 not been exceeded (nor in some respects equalled) 

 by any astronomer whether professional or otherwise. 

 I speak, let it be observed, of accuracy of definition, 

 such as is necessary to display minute points of 

 light, like the satellites of Uranus. In respect of 

 the amount of illumination requisite for the display 

 of many diffuse faint objects among the nebulae, the 

 gigantic telescopes of Herschel and Lord Rosse are 

 of course superior. 



(285 1 ^ r -kassel's observatory near Liverpool was erected 

 Hisinstru- in 1840. The principal instrument is a reflecting 

 ments. telescope of 24 inches aperture (completed, however, 

 only some years later), mounted equatoreally, an ar- 

 rangement requiring great mechanical skill, but, as 

 the results show, most effectually accomplished. The 

 speculum was worked and polished by machinery con- 

 structed by Mr Nasmyth, but principally devised by 

 Mr Lassell, after he had examined and tried Lord 

 Rosse's method. I should think it must be admitted 

 to be the most perfect optical work of its kind ever 

 made : for I believe there is no test object in existence 

 which Mr Lassell has not seen with it ; in fact he 

 has discovered the most delicate tests himself, the 

 6th star of the group 6 Orionis (though not first seen 



by him), a satellite of Neptune, an eighth satellite of 

 Saturn, and several satellites of Uranus. 



Not many days had elapsed after the discovery of (286.) 

 Neptune, before Mr Lassell, directing his telescope He disco- 

 to it, perceived a satellite (as he believed) on Oct. l^^ s *~ 

 10, 1846. The discovery was fully made out in the Neptune, 

 following year, and was soon after verified by the 

 great refractors of Pulkowa and Western Cambridge 

 (U.S.) Its period is about 5'879 days, 1 and its dis- 

 covery was of singular importance as leading to a 

 knowledge of the mass of the planet. 



Till 1848 only seven satellites of Saturn were ad- (287.) 

 mitted. The two closest to the planet were detected and one of 

 by Sir William Herschel in 1789, and have been Saturn - 

 seen by very few astronomers since. During five 

 years'* residence at the Cape, Sir John Herschel never 

 but once obtained even a doubtful glimpse of the 

 closest with an 18-inch mirror. The third, fourth, 

 and fifth were discovered by Cassini in 1684 ; the 

 sixth and most conspicuous by Huygens in 1654 : the 

 outermost by Cassini in 1671. To these an eighth 

 satellite, intermediate in position between the two 

 last, was added by Mr Lassell on the 19th September 

 1848. By a singular coincidencej.it was recognised 

 as a satellite the very same evening by Mr Bond of 

 Cambridge (in America) with the great Munich re- 

 fractor. The new body was called Hyperion, in con- 

 formity with Sir John Herschel's suggestion of distin- 

 guishing the satellites as well as the planets by mytho- 

 logical names. On the 22d November 1850 Mr Las- 

 sell saw at once Saturn with his whole train of eight 

 satellites a glorious spectacle probably enjoyed by no 

 other astronomer. In the same month of November Faint ring 

 Mr Bond discovered a faint or dusky ring of Saturn f Saturn 

 interior to the two long known. It is probably ne- 1, 18 ^ 6 " 

 bulous, for by Mr Lassell' s observations and Mr Bond. 

 Jacob's it appears to be transparent. 



Sir William Herschel thought that he recognised 

 six satellites of Uranus. The second and fourth 

 his table have been observed by several astronomers, 

 particularly Sir John Herschel and M. Lamont. 

 Their periods are 8 d I7 h and 13 d ll h . To these Mr 

 Lassell, aided by the fine climate of Malta (to which 

 for two seasons he removed his telescope), has con- 

 clusively added two more : one, appearing to coin- 

 cide with the closest of HerschePs, of which the 

 period is 4 d 3 h 28 m , and one still nearer the planet 

 revolving in 2 d 12 m 29 s , the shortest orbital revolu- 

 tion in the solar system. Mr Lassell doubts se- 

 riously the existence of any other satellite. 2 



(288.) 



1 From Mr Lassell's observations at Malta, 1852-3. 



2 See Astron. Society's Notices, xiii. 151 ; and xiv. 133. 



