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90 The comet returned to perihelion in Nov. 1832 within 12 hours of the time predicted by Santini. It was first seen at Rome on Aug. 23, but owing to its excessive faintness was not generally observed till two months later.

The next return was calculated to take place on July 13, 1839, but, in consequence of its close proximity to the Sun, the comet was not seen on that occasion.

Santini continued his researches and fixed on Feb. 11, 1846, for the next perihelion passage. This was anticipated by astronomers with great eagerness, because it was foreseen that the comet would be visible for a considerable period, and so there would be the chance of obtaining a good body of observations for correcting the theory of its motion. Di Vico at Rome discovered it on Nov. 28, 1845, and Galle at Berlin found it two days later; but it was not generally seen till the 2nd or 3rd week in December. The striking incident of the comet breaking up into two portions, alluded to in a previous chapter, deserves further description.

The duplicity of Biela's Comet appears to have been first seen on Jan. 13, 1846, at Washington, U.S. Three weeks previously to this, however, Hind remarked a kind of protuberance towards the North of the nucleus which perhaps may be regarded as the first sign that something unusual was going to be developed. Two days after the American observation, that is to say on Jan. 15, Challis at Cambridge noticed for the first time the complete severance of the little comet from the big one. His description of what he saw, and his comments on the occurrence, are so very interesting as to deserve transcription. He published his notes in a letter to the President of the Royal Astronomical Society.

"On the evening of Jan. 15, when I first sat down to observe it, I said to my assistant, 'I see two comets.' However, on altering the focus of the eye- glass and letting in a little illumination, the smaller of the two comets appeared to resolve itself into a minute star, with some haze about it. I observed the comet that evening but a short time, being in a hurry to proceed to observations of the new planet. On first catching sight of it this evening (Jan. 23) I again saw two comets. Clouds immediately afterwards obscured the comet for half an hour. On resuming my observations I