Page:The story of the comets.djvu/84

50 year get into the periodicals as Comet No. 3 of a year, but would have to have its number altered subsequently during the year and have become No. 2 when the index was compiled. As comet discoveries multiplied the confusion became intolerable; hence the system now in vogue of letters of the alphabet as provisional designations, not to be replaced by numbers until a sufficient time has elapsed to make it certain that no disturbance of the order of perihelion passage could reasonably be anticipated. The credit of settling the present system on its existing basis is due to Dr. C. A. F. Peters, the editor of the German Periodical, Astronomische Nachrichten, expanding in 1872 a system suggested by the German Astronomical Society (The "Astronomische Gesellschaft") in 1867, but which missed its mark because it took no account of the order of discoveries being very often different from the order of perihelion passage. It remains to be seen whether photography will give cause to the creation of fresh confusion arising from the fact that a photograph plate will "take" a comet and the plate may remain (as has happened) unexamined, and the existence thereon of a comet unknown, for weeks, or it may be for months, after the photographer has performed his share of the work.

An attempt was made some years ago to introduce the use of a couplet of names in the case of a comet proved to be periodic by reason of its making a second visit to us. Thus, the comet found in 1812 by Pons, was rediscovered in Sept. 1883 by Brooks. When the identity of the Comet of Sept. 1883 (which is now enrolled as 1884, i.) with that of 1812 became certain, it was called by American writers the "Pons-Brooks Comet", but the practice has happily not spread, and is not commendable. The awkwardness of it is shown in the following cryptogram: The "Tempel (3)-Swift" Comet, which means the third of the periodical comets discovered by Tempel, which was afterwards rediscovered by Swift and taken to be a new comet.

It has already been stated that the identification of a new