Page:The story of the comets.djvu/95

VI. was that he was able to assure himself of the identity of the Comet of 1818 with the 3 comets just mentioned, and that between 1786 and 1818 it had passed through perihelion 7 times without being noticed. But Encke was not content to let the matter rest there so he proceeded to calculate the date of the comet's next return, and found himself justified in announcing that the comet would arrive at perihelion on May 24, 1822, after having been retarded about 9 days by Jupiter.

"So completely were these calculations fulfilled, that astronomers universally attached the name of 'Encke' to the Comet of 1819, not only as an acknowledgement of his diligence and success in the performance of some of the most intricate and laborious computations that occur in practical astronomy, but also to mark the epoch of the first detection of a comet of short period one—of no ordinary importance in this department of science."

It unfortunately happened that in 1822 the position of the comet in the heavens was such as to render it only visible in the Southern hemisphere. It was therefore systematically watched by only one observer, Rümker, who discovered it on June 2 at the private observatory of Sir T. M. Brisbane at Paramatta. N.S.W., and he was only able to follow it for 3 weeks. Rümker's observations were however so far valuable that, besides showing that the comet actually did come back, they furnished Encke with the means of predicting with greater certainty its next return which he found would occur on Sept. 16, 1825. On this occasion it was first seen on July 13 by Valz, but was discovered independently by other astronomers. Cacciatore of Palermo described it as being round, with a faint nebulosity, and about 1° 30' in diameter.

The next return to perihelion took place on Jan. 9, 1829. Struve at Dorpat found it on Oct. 13, 1828. Harding at Göttingen and Gambart at Marseilles both saw it for the first time on the same day, Oct. 27, the former having been on the look out for it since August 19. On Nov. 30 it was visible to the naked eye as a star of the 6th magnitude, and the week afterwards it had become as bright as a star of the 5th