THE URANIAN SATELLITES, ARIEL AND UMBRIEL.—The following positions of the two interior satellites of Uranus for the ensuing fortnight are derived from the data furnished by Mr. Marth in the January number of the Monthly Notices of the Royal Astronomical Society, and are for 11h. G.M.T., or about the time of the planet's meridian transit. There must be many telescopes in this country which will command the two exterior satellites, Titania and Oberon, but, so far as we know, neither Ariel nor Umbriel have yet been certainly observed here with any but Mr. Lassell's reflectors. Prof. Newcomb states that Ariel is intrinsically brighter than Umbriel; he thinks that Ariel at least belongs to that class of satellites of which the brilliancy is variable, and dependent on its position in its orbit, and he adds that the evidence of variability of some kind seems indisputable, since he has repeatedly failed to see it with the Washington refractor when the circumstances—distance from the primary not excepted—were favourable, and when the next satellite, Umbriel, though leas favourably situated, was visible. “On the other hand”, he remarks, “there were two occasions, 1874, January 28, and 1875, March 25, when it was surprisingly conspicuous” and at these times the angle of position was about 350°. Prof. Newcomb further expresses the opinion that where any difficulty is experienced in seeing the outer satellites, he would not hesitate to pronounce it impossible to see the inner ones.