Page:The fairy tales of science.djvu/248

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unlikely, and to which many members of our family are liable.

Another Comet of short period is the one called after Mr. Biela, of Josephstadt, who, at its apparition in 1826, identified it with Comets that had appeared in 1772 and 1805. The time of its revolution is about 6 2/3 years. It has since been observed in 1832, 1839, 1845-6, and 1852—in the two last years as a double Comet.[1]

A Comet discovered by M. Faye, in 1843, describes an elliptic orbit in a period of 7 1/2 years, and has been observed on its return in 1850.

Two other Comets—the one discovered by De Vico, in 1844, the other by Brorsen, in 1846—have each a period of about 5 1/2 years. Another, finally, discovered by d’Arrest, in 1851, in the constellation Pisces, has a period of 7 years.

Before I take my final leave of you, I may still

  1. At the return of Biela’s Comet, in 1845-6, a most singular phenomenon was observed. The Comet appeared at first, as usual, as a single body; but on its approach towards perihelion it was, on the 13th January, 1846, for the first time, seen to be attended by another Comet considerably fainter, at a distance of about 2′. This distance continued steadily to increase, with a corresponding change in the comparative brightness of the two Comets, till the companion Comet became as bright as the original, and subsequently brighter, exhibiting a star-like nucleus; a very short time after, however, the original Comet gained again in brilliancy on its companion, which finally disappeared some time before the other ceased to be observed.