Page:The story of the comets.djvu/80

CHAPTER V.

THE DISCOVERY AND IDENTIFICATION OF COMETS.^[1]

How Comets are discovered.—The great French Comet-hunter, Messier.—Much Comet-hunting now carried on in America.—Suitable occupation for amateur astronomers.—Designation of Comets.—Appropriation of observers' names to Comets.—Comets only identified by the elements of their orbits.—Physical appearance of Comets no certain proof of identity.—Identity of elements not always conclusive.—Possibility of more than one Comet following the same path.—Photography as an aid to the discovery of Comets.—Ancient Chinese records of great value.—Medals for successful Comet-hunters.—Telegraph codes for transmission of cometary announcements.

"How does a new comet become known?" "Who looks out for comets?" "Who organises observations of comets?" These are questions which are often asked, and which are seldom answered in set terms in the text-books; and therefore it may be worth while to devote a short chapter to the subject.

In early times and down to the invention of the telescope and for quite a century and a half after that event, the discovery of comets may be said to have been left to chance: in other words they discovered themselves; that is to say, manifested themselves to anybody who happened to be looking at the heavens by night. It was not until 2 French astronomers towards the close of the 18^th century took up the matter that any definite effort seems to have been made systematically to watch for or to search for comets. Messier, whose first comet dates from 1760, and Pons, whose first comet dates from 1802, are the 2 Frenchmen here referred to,

1. Some useful hints on the search for and observation of comets by Denning will be found in the well-known and useful American Magazine, Popular Astronomy, vol. x, p. 69. Feb. 1902.