SATIN

Its light, whence it is inferred that it revolves on its axis in the same time in which it completes its orbital revolution. Satellites of Uranus Sir John Herschel remarks, that with the exception of the two interior satellites of Saturn, the attendants of Uranus are the most difficult objects to obtain a sight of, of any in our system. Their existence was first discovered by Sir William Herschel, who suspected their number to be six; but he was only able to obtain micrometrical measures of the distance of two of them, and only those two have yet been seen by any other astronomer. Sir W. Herschel's observations are given in the Phtl. Trans, for 1788 and 1797, and again in the vol. for 1815. They were made between the years 1787 and 1798; and from' the latter period until 1828, the planet having been unfavourably situated, these satellites remained unobserved, and had even fallen out of notice. Between the latter year and 1834 a series of observations, recorded in the Memoirs of the R. Astr. Society, vol.viii., were made by Sir John Herschel for the purpose of Verifying his father's results, which, with respect to two satellites, were confirmed in the amplest manner. The periodic times deduced from his observations are respectively 8 d. 16h.56m. 31-3 sec, and 13d. lib. 7m. 12-6 sec. The orbits are nearly circular, and almost perpendicular to the ecliptic, being inclined to that plane in an angle of 78° 68'; and what is extremely remarkable, as contrary to the otherwise unbroken analogy of the solar system, the motions of the satellites in their orbits are ret i-ograde, or from east to west. The following table shows the distances (in radii of Uranus) and periods of all the satellites, according to Sir William Herschel. (.HerscheVs Astronomy, Cab. Encyc.) 1 Mean Distance. Sidereal Period. d. h. m. s. 1? 13-1?0 5 21 25 0 2 17-022 8 16 56 5 3? 19-845 10 23 4 0 4 22-752 13 11 8 59 6? 45 507 33 1 48 0 6? 91-008 107 16 40 0 [s. 1095]