382 SCIENTIFIC RECORD FOR 1885. 



tions of comets, including the present recorded returns of periodic 

 comets, is considerably greater : 



D'Arrest's comet lias been observed 4 times. 

 Biela's comet has been observed 6 times. 

 Brorsen's comet has been observed 5 times. 

 Encke's comet has been observed 23 times. 

 Faye's comet has been observed G times. 

 Halley's comet has been observed 7 times. 

 Pons's comet has been observed 2 times. 

 Tempel's (1) comet has been observed 3 times. 

 Tempel's (2) comet has been observed 2 times. 

 Tempel's (3) comet has been observed 2 times. 

 Tuttle's comet has been observed 3 times. 

 Winnecke's comet has been observed 4 times. 



Accordingly, 67—12=55 repeated apparitions are to be added, bring- 

 ing up to 357 the total of the observed appearances of comets. In this 

 summary, of course, no allowance is made for the great uncertainty of 

 many of the older orbits, or for the fact that in some cases it is doubt- 

 ful whether the same periodic comet has been seen. 



The comets are arranged strictly in the order of their perihelion pas- 

 sage. This is a long-established system and one i)ossessiug numerous ad- 

 vantages ; furthermore, it has lately been made the rule of the Astronom- 

 ische Gesellschaft. The uncertainty sometimes existing in the designa- 

 tion of particular comets during the year of discovery can always be 

 easily removed, for the time being, by the addition of the name of the 

 discoverer. Moreover, a strict adherence to this system of numbering 

 comets in each year has become necessary of late, partly on account of 

 tbe great number of comets discovered, and i)artly on account of the con- 

 siderable increase of the known periodic comets during the last forty 

 years. The actually observed returns of these comets must of course be 

 arranged with the other comets. Since in many cases the periodicity has 

 first been established at the second apparition, and in a few cases at the 

 third, the exclusion of periodic comets from the list of apparitions of 

 each year would frequently cause annoying changes in the designa- 

 tions of earlier years. In the publications of the past ten years the 

 periodic comets, particularly, have led to a great many diflFerences in 

 the designation of comets, an evil which is not merely of a theoretical 

 nature, but, for those who often have occasion to refer to the literature 

 of comets, is one which carries with it very real and practical incon- 

 veniences, frequently necessitating much troublesome comparison of 

 observations, or of ephemerides, to decide what comet is really referred 

 to. Esi)ccially in years in which a great many comets are seen, if the 

 names of the discoverers are not given, not only is there great loss of 

 time, but besides this mistakes easily occur. 



