From observations with large modern instruments it appears highly probable that the four known satellites, must be considerably larger than any others which may be revolving round the planet. A curious fact in connection with these satellites is that their motions are retrograde.
Apparent Orbits of the Satellites of Uranus, as seen in an Inverting Telescope.
(The small circle in the above diagram represents the planet and is on the same scale as the orbits. The arrows show the direction of the motion of the satellites, and the figures indicate the number of days from the time of the last North elongation.)]
_Discovery of Neptune._—The leading incidents in the narrative of the discovery of Uranus and Neptune present a great dissimilarity—Uranus was discovered by accident, Neptune by design. Telescopic power revealed the former, while theory disclosed the latter. In one case optical appliances afforded the direct means of success, while in the other the unerring precision of mathematical analysis attained it. The telescope played but a secondary part in the discovery of Neptune, for this instrument was employed simply to realize or confirm what theory had proven.
Certain irregularities in the motion of Uranus could not be explained but on the assumption of an undetected planet situated outside the known boundaries of the system. Two able geometers applied themselves to study the problem of these irregularities, and to deduce from them the place of the disturbing body. This was effected independently by Messrs. Le Verrier and Adams; and Dr. Galle, of Berlin, having received from Le Verrier the leading results of his computations, and the intimation that the longitude of the suspected planet was then 326°, found it with his telescope on the night of Sept. 23, 1846, in longitude 326° 52′. The calculated place by Prof. Adams was 329° 19′ for the same date and less accurate than the prediction of Le Verrier. The former had priority both in attacking the problem and resolving it, though unfortunately his efforts were not backed up in a practical way. But for the supineness of certain officials, there is little doubt that the planet would have been telescopically discovered in the autumn of 1845, when it was within 1° 49′ of the place attributed to it by Prof. Adams. Delays occurred owing to the doubts prevailing, and in the meantime the planet was found elsewhere. This circumstance does not rob Prof. Adams of his hard-earned laurels, though it shows how seriously official negligence can mar the character of a discovery.