Page:The story of the comets.djvu/105

VI.

A comet was discovered by Pons on June 12, 1819. Encke assigned to it a period of 5$1⁄2$ years, which, as the table shows, was a very close approximation to the truth. It was not, however, seen from that time till March 8, 1858, when it was detected by Winnecke at Bonn, and by him regarded as a new comet; but he soon ascertained the identity of the 2 objects. It must have returned in 1863 but was not then favourably placed for observation. The next return to perihelion occurred in June 1869. It was discovered by Winnecke himself on April 9 of that year, and is described by him as being faint, but as much as 6' or 8' in diameter. Some calculations by Oppolzer led him to think that this comet was observed previously to the occasion which has usually been regarded as its first discovery (namely, its detection by Pons in 1819) and that it is identical with the comet discovered by Pons in February 1808, which was only visible for 3 days and whose orbit was never calculated.

Visible again in 1875, but missed in the autumn of 1880, its next return was in 1886, when it was seen only in the Southern hemisphere after perihelion. It passed its perihelion 12 days earlier than it was predicted to do, and Oppolzer considered that its movements could not be completely explained by the theory of gravitation alone, but that the existence of some resisting medium was indicated: thereby confirming, according to the knowledge of 20 years ago, the theory then current as to the movements of Encke's Comet, spoken of on a previous page, but which theory has otherwise remained unconfirmed. This comet was observed in 1892 and 1898, but missed in 1904, in which year its perihelion passage was fixed for Jan. 21. Let us hope it may be seen 1909-10.

This comet was detected by Brorsen at Kiel on Feb. 26, 1846. The observations showed an elliptic orbit, and the