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comets. Within a fortnight of this date, however, the comet had actually separated into two distinct nebulosities, which travelled along in company for more than three months. The circumstance was remarked independently by various astronomers, but the division appears to have been first perceived in America on the 29th of December. At the end of January and until the end of March the two comets were very generally observed: Mr. Otto Struve thought he could just distinguish the companion on the 16th of April, when the principal comet was observed for the last time with the great Equatorial at Pulkova. The apparent distance between the centres of the two nebulosities was at first little more than two minutes, but subsequently it increased to about seven times that quantity, and each head or comet exhibited a short tail in the usual direction, while something very like a stellar point was observable in each. The companion comet was even the brighter of the two about the 12th of February, but did not continue so more than three or four days. The real distance between the comets has been calculated by Professor Plantamour for different days: we subjoin some of his results, expressed in English miles, instead of semidiameters of our globe :

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March was therefore about two-thirds of the moon's mean distance from the earth. The angle of position of the line joining the two heads in respect to a fixed point, altered very little, according to Professor Plantamour's researches.

Biela's comet reappeared at the end of August, 1852, and continued visible about three weeks. Professor Secchi, of Rome, detected, on September 16th, a fainter comet near the above, which it preceded by two minutes of time in right ascension, being 30′ south. This object was considered to be, in all probability, the second part of the chief comet; and, if so, it had evidently become a distinct body, since its real distance from the other must have exceeded 1,250,000 miles. The morning twilight greatly interfered with observations this year.

The dimensions of the orbit of Biela's comet in 1846 were as subjoined:

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CHAPTER VII.

OTHER COMETS OF SHORT PERIOD-FAYE'S, DE VICO'S, BRORSEN'S, D'ARREST'S.

The Periodical Comet of Faye.

NEARLY a quarter of a century after the discovery of the periodicity of Encke's comet, another object of great interest was brought to light by M. Faye, one of the astronomers attached to the Observatory of Paris. On the 22nd of November, 1843, he detected a telescopic comet in the northern part of the constellation Orion, which was visible till the 10th of April following. It exhibited a bright star-like nucleus, with a short, fan-shaped tail, in the usual direction, but was never bright enough to be discovered without optical aid. The incompatibility of the track which the comet was pursuing with the assumption of parabolic motion, appears to have been independently remarked about the same time by Professor Argelander of Bonn, Dr. Goldschmidt of Göttingen, and Professor Henderson, late director of the Royal Observatory at Edinburgh, who occupied themselves in the investigation of the true curve described by the comet. This was speedily found to be an ellipse, with a period of revolution of about 71⁄2 years, or rather

longer than in the case of Biela's comet. A good deal of speculation followed with regard to the identity of the new comet with one observed by Messier in 1770, which was known to have suffered enormous perturbations through the attraction of Jupiter. The question was not set at rest till after the of a appearance complete memoir on the subject, by M. Leverrier, who, in tracing the past history of the comet of Faye, has proved that it could not have been the same as that of 1770, designated the 'lost comet;' but it must, notwithstanding, have been a denizen of our system for at least ninety-six years previous to its discovery by Faye. It is possible that in its descent towards the sun in 1747, when it passed close to the planet Jupiter, the action of this vast globe may have deflected the comet into its present orbit, and this is the least remote period at which disturbances to the amount necessary to produce a great change could have occurred.

M. Le Verrier predicted that Faye's comet would again reach its perihelion on the 3rd of April, 1851, at midnight, but its path amongst the stars would not be so favourable for observations in Europe as at the previous appearance. True to the prediction, the comet was in sight with the large telescope under the direction of Professor Challis, at Cambridge, and actually attained its least distance from the sun at the very hour named by the French mathematician some years beforehand, having suffered a retardation of between seven and eight days, chiefly through the influence of Jupiter, as M. Le Verrier had calculated. The exact length of the comet's revolution in 1843 was

2,718 days, and the elements necessary to construct the orbit at that epoch are as subjoined :—

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The other elements will be found in the catalogue of orbits (1843, III.)

The comet of Faye may be expected to arrive at perihelion again in October, 1858.

The Periodical Comet of De Vico.

On the 22nd of August, 1844, Father de Vico discovered a telescopic comet at the Collegio Romano at Rome, which continued visible in powerful telescopes until the end of the year. About the third week in September it was just discernible with the naked eye, and under slight optical aid had a very beautiful appearance, the nucleus being bright and star-like, and a short tail of a bluish tinge, extending in the direction opposite that of the sun. It was soon found by M. Faye and others that the observations would not agree with the assumption of parabolic motion, and on investigating the real nature of the conic section described by the comet it was ascertained to be an ellipse with a periodic time of about five and a half years. The elements have been calculated by Dr. Brünnow, with due regard to the influence of planetary attraction during the interval over which the observations extend, and his results show that at the time of perihelion passage the length of the comet's

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