Page:The story of the comets.djvu/83

V. takes its name from, not its first discoverer who was Montaigne in 1772, nor its second discoverer Pons in 1805, but from its third discoverer Biela in 1826. Then again, the comet universally called "Encke's" takes its name from a man who possibly never saw it at all until after the time when his name had become permanently attached to it. But he dedicated so vast an amount of time and labour to an examination of its orbit that astronomers with one consent coupled his name to it. Nowadays it is usual to identify comets first of all temporarily by an italic letter of the alphabet joined to the year of discovery, and then afterwards by an ordinal number which indicates the order of the date of its perihelion passage amongst the comets of a particular year. Thus, Morehouse's Comet was first of all "Comet c of 1908", but it is permanently enrolled as the 4th Comet of 1908, usually printed as "Comet iv. 1908", or "the Comet of 1908 (iv.)".

A word of caution is perhaps desirable in connection with the system now in vogue of numbering the comets of a year. It was a long time before the system became settled, and previous to that being the case things were in great confusion; and the old confusion is even now operative to lead astray persons hunting up old comets in the indexes to Scientific Publications prior to 1872. It seemed very obvious to number the comets of a year in succession according to the dates of their discovery from January to December, but this pre- supposed that they passed perihelion in the same chronological order in which they were discovered. This, however, would be by no means always the case, so that, for instance, the 3rd comet in the order of discovery might prove to be the 2nd in the order of perihelion passage; and it might during the