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pected at first sight that both comets had moved. This suspicion was afterwards confirmed: the two comets have moved in equal degree, retaining their relative positions. I compared both with Piazzi, 0^h 120, and the motion of each in 50^m was about 7^s in R.A. and 10" in N.P.D. What can be the meaning of this? Are they two independent comets? or is it a binary comet? or does my glass tell a false story? I incline to the opinion that this is a binary or double comet, on account of my suspicion on Jan. 15. But I never heard of such a thing. Kepler supposed that a certain comet separated in two, and for this Pingré said of him, 'aliquando bonus dormitat Homerus.' I am anxious to know whether other observers have seen the same thing. In the meanwhile I thought, with the evidence I have, I had better not delay giving you this information."

In a subsequent letter Professor Challis says:—

"There are certainly two comets. The north preceding is less bright and of less apparent diameter than the other, and, as seen in the Northumberland telescope, has a minute stellar nucleus. . . .

"The greater apparent distance between the comets on Jan. 24 is partly accounted for by their approaching the Earth. I saw the comets on Jan. 25, but took no observation. The relative positions were apparently unchanged.

"I think it can scarcely be doubted, from the above observations, that the two comets are not only apparently but really near each other, and that they are physically connected. When I first saw the smaller, on Jan. 15, it was faint, and might easily have been overlooked. Now it is a very conspicuous object, and a telescope of moderate power will readily exhibit the most singular celestial phenomenon that has occurred for many years a double comet."^[1]

The comets continued to be observed all through February and March. On March 24 one only was visible, and on April 22 both had disappeared. To O. Struve on Feb. 21 there appeared no material connection between the 2 bodies; but some days later Maury at Washington saw an arc of light extending from the large comet to the small one, forming a sort of bridge between the two. This was when the small comet was at its brightest. When the large comet had regained its superiority it threw out new rays, which gave it the appearance of having 3 tails, each adjacent tail making an angle of 120° with its neighbour, one of the tails being the bridge to the small comet.

Maury's words were:—

"No. 2 appears to have thrown a light arch of cometary matter from its head over to the other: and their tails stretching off below in the field, and nearly in a parallel direction, gives these 2 objects the singular and beautiful

1. Month. Not. R.A.S., vol. vii, p. 73. March 1846.