698 PROGRESS OF ASTRONOMY FOR 1891 AND 1892. 



COMETS. 



In a series of i^apers in the Bulletin Astronomiqne M. Schulhof has de- 

 veloi)ed in an interesting' way tlie relations existing between the elements 

 of a comet's orbit before and after it suffers jierturbation by a planet. 

 That the periodic comets of our system have been captured through the 

 perturbing action of planets apfjears established; and Mercury has four 

 comets assigned to it, Venus seven, the Earth ten. Mars four, Jupiter 

 twenty-three, Saturn nine, Uranus eight, Neptune five, and a- further 

 group of comets appears to give a feeble indication of an ultra-Xeptu- 

 niaii planet at a distance from the sun of about seventy times that of 

 the earth. 



The search for new comets has been systematized by the cometary sec- 

 tion of the British Astronomical Association under the direction of Mr. 

 W. F. Denning. The aims of this section are to secure observations of 

 comets, to discover new comets and nebuhie, to record telescopic me- 

 teors, etc. It is intended to sweep the sky regularly for new comets, a 

 definite region being assigned to each observer according to convenience , 

 and choice. 



The following notes, relating chiefiy to the comets of 1891 and 1892, 

 will comidete the list of comets published in these "Reports of Progress," 

 from 1883 to 1892. It is hardly necessary to remark that the most 

 complete and authoritative annual summary of cometary phenomena is 

 that published by Dr. Kreutz in the Vierteljahrsschri/t der Astronom- 

 ischen Geselhch ((ft. 



The arrangement adopted below is the order of i^erihelion passage, 

 except in the case of well-known periodic comets, such as Encke's, 

 Winnecke's, etc., which are arranged alphabetically by their recognized 

 names. The table of elements appended is to l)e regarded as only 

 approximate, but is suflicient to furnish an idea of the general form 

 and position of the orbit. 



( 'Omet Encke: The return of Encke's well-known periodic comet; 



-=Comet 1891, III. j^^st found by Barnard, from the ephemeris, on Aug- 

 ust 1, 1891. It was then exceedingly taint, but in September it had 

 increased to a nebulous mass of ubout the sixth to seventh magnitude. 

 The comet was unfavorably situated for observation after the end of 

 September, the last observation reported being October 11. It is note- 

 worthy that its ]iath at this return was almost the stime as in the return 

 of 1858, and a comparison of the brightness on these two occasions 

 would seem to indicate that it has not undergone any material change 

 in physical condition during the interval. 



Comet Tempel. — Tempel's first periodic comet, and of rather unusual 

 interest, was unfortunately missed at its return in 1892, being unfavor- 

 ably situated for observation. 

 Comet Tempela-Swift: This periodic comet returns to the sun 



=::Comet 1891 V. ouce in every five' and a half years, but un- 



