This comet is small and hardly visible to the naked eye, even when brightest. Nevertheless, as if to make up for its seeming insignificance by the interest attaching to it in a physical point of view, it exhibited, at its appearance in 1846, a phenomenon which struck every astronomer with amazement, as a thing without previous example in the history of our system. It was actually seen to separate itself into two distinct comets, which, after thus parting company, continued to journey along amicably through an arc of upward of 70° of their apparent orbit, keeping all the while within the same field of view of the telescope pointed toward them. The first indication of something unusual being about to take place might be, perhaps, referred to the 19th of December, 1845, when the comet appeared to Mr. Hind pear-shaped, the nebulosity being unduly elongated in a direction inclining northward. But on the 13th of January, at Washington, in America, and on the 15th and subsequently in every part of Europe, it was distinctly seen to have become double; a very small and faint cometic body, having a nucleus of its own, being observed appended to it, at a distance of about 2′ (in arc) from its centre, and in a direction forming an angle of about 328° with the meridian, running northward from the principal or original comet. From this time the separation of the two comets went on progressively, though slowly. On the 30th of January the apparent distance of the nucleus had increased to 3′, on the 7th of February to 4′, and on the 13th to 5′, and so on, until on the 5th of March the two comets were separated by an interval of 9′ 19″, the apparent direction of the line of junction all the while varying but little with respect to the parallel. During this separation, very remarkable changes were observed to be going on, both in the original comet and its companion. Both had nuclei, both had short tails, parallel in direction and nearly perpendicular to the line of junction; but whereas at its first observation, on January 13th, the new comet was extremely small and faint in comparison with the old, the difference both in point of light and apparent magnitude diminished. On the 10th of February they were nearly equal, although the day before the moonlight had effaced the new one, leaving the other bright enough to be well observed. On the 14th and 16th, however, the new comet had gained a decided superiority of light over the old, presenting at the same time a sharp and star-like nucleus, compared by Lieutenant Maury to a diamond spark. But this state of things was not to continue. Already, on the 18th, the old comet had regained its superiority, being nearly twice as bright as its companion, and offering an unusually bright and star-like nucleus. From this period the new companion began to fade away, but continued visible up to the 15th of March. On the 24th the comet appeared again single, and on the 22d of April both had disappeared.