SATELLITE

The recent discovery of an eighth satellite in the system of Saturn may be regarded as the natural consequence of the increased optical power of the instruments now applied to astronomical observations, but it was by a singular chance that the discovery was made both in England and America on the very same day, — the ISth of September, 184S. In order to avoid the confusion which has arisen from the practice of designating the satellites of Saturn by numbers, applied sometimes with reference to the order of discovery and sometimes to the order of distance. Sir John Herschel proposed to distinguish the individuals of this system by names, and in conformity with the nomenclature adopted by him (the names of the Titanian divinities), both discoverers of the new satellite gave it the name of Hyper i on. Commencing with the one nearest the planet, and taking them in the order of distance, the numes of the eight satellites at present known are as follows. — Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Hyper i on, lapetus. Of these bodies Titan is by far the largest, and supposed to be nearly equal in size to the planet Mars. Mimas and Enceladus are the two discovered by Sir W. Herschel, interior to the ring, and so small that they can be seen with great difficulty even in the best telescopes. Hyper i on is pmbably not greater than Mimas, but more easily seen on account of its greater distance from the planet. Prior to its discovery the interval between Titan and lapetus was so great as to destroy the analogy which seemed to prevail in the other cases, and to leave, as it were, a large gap in the system, similar to that in the solar system between Mars and Jupiter before tlie discovery of the small planets. From this circumstance, and also from the smallne of Hyper i on. Sir J. Herschel has surmised the probability of other minute satellites revolving at the same mean distance. Of the six satellites of Uranus seen or suspected by Sir William Herschel, the existence of two only has been confirmed by the observations of other astronomers. Some others have been seen by La ell and by Otto Struve; but none of them appear to be identical with those observed by Sir W. Herschel. The remaining two are still doubtful. One satellite of Neptime has been repeatedly observed, both by La ell and O. Struve. The existence of a second, suspected by La ell, has not yet been verified. [s. 1413]