Notices respecting New Books. 303 



observation of phenomena so interesting in themselves, and so im- 

 portant in reference to the light which they throw on the constitution 

 of the solar system. 



Chap. VI. Observations of the Satellites of Saturn. 



" During the years 1835, 1836 and 1837, the ring of Saturn and 

 the orbits of the satellites were sufficiently open to permit the accu- 

 mulation of a considerably extensive series of their angles of position 

 with the meridian, or with the longer axis of the ring, so disposed 

 as to be available towards the more exact determination of their 

 orbits ; of which little is known with the exception of that of the 

 sixth, which is the largest and most easily observable, and whose 

 elements and perturbations have been made the subject of elaborate 

 investigation by Bessel." The author therefore considers that his 

 observations of those bodies, " though confessedly imperfect, owing 

 to their extreme faintness in the equatorial, and the difficulty of ob- 

 taining any measures at all of position with the 20-foot reflector out 

 of the meridian, may not be wholly without interest as a contribu- 

 tion to their theory." 



The number of known satellites belonging to Saturn is seven, — 

 of which one was discovered by Huygens, four by D. Cassini, and 

 the remaining two by Sir William Herschel. The two last are ex- 

 tremely small and faint ; and so long was it before the observations 

 of the discoverer were confirmed, that some astronomers began even 

 to entertain doubts of their existence. Such, indeed, is their extreme 

 minuteness, that it is only under the most favourable circumstances, 

 and with telescopes of extraordinary power, that they can be per- 

 ceived. The three which are most remote from the planet may be 

 seen with telescopes of moderate power. " Measures of the fourth 

 satellite could rarely be procured so as to be in any degree satisfac- 

 tory with the equatorial — of the third, never As to the two in- 

 terior satellites, it is needless to state that no glimpse of either of 

 them was ever obtained with this instrument." In fact, the one 

 nearest the planet was only observed once in the 20-foot reflector. 



The satellites of Saturn had hitherto been distinguished merely by 

 the ordinal numbers, first, second, third, and so on ; and it is the 

 usual, though not uniform practice, to begin with the satellite near- 

 est the central body and reckon outwards. But the discovery of 

 the two interior satellites necessarily deranged the nomenclature, the 

 one which had been previously reckoned the first now becoming the 

 third. Some astronomers have also adopted the contrary order, and 

 begun the numeration with the most remote satellite. Sir John 

 states, that having found the equivoque practically annoying, and a 

 source of frequent error and mistake, he had recourse to the practice 

 of distinguishing them by individual names, adopting a mythological 

 nomenclature, which, however, he does not " pretend to recommend 

 to others, though persuaded that some nomenclature other than the 

 equivocal one in actual use will be found necessary by all who ob- 

 serve these bodies." The names which he selected are the following, 

 beginning with the most remote, and proceeding downwards in order : 



