ASTRONOMY. 95 



closely represented by the alteration of a single term in 

 Hansen's tables. The question whether this alteration is 

 admissible in the theory cannot yet be decided. 



COMETS. 



The recent dearth of comets has been supplied in 1877 by 

 the discovery of five. Comet a was discovered by Borelly, 

 of Marseilles, on February 8, and was visible as a telescopic 

 object till March 18 in Europe, but was observed by the 26- 

 inch telescope at Washington so late as March 30. It had 

 the usual comet spectrum. Comet b was discovered by Win- 

 necke, of Strasburg, on April 5. Young, of Dartmouth, and 

 Wolf, of Paris, have investigated its spectrum, which 4s of 

 the usual type. Comet c was discovered by Swift, of Roch- 

 ester, on April 10, and independently by Block, of Odessa, 

 on the same date, and by Borelly on the 14th. Cornet b 

 remained a tolerably bright object until some time in July. 

 Comet c was always faint. There is a strong resemblance 

 between the elements of comet c and those of the comet of 

 1762, but the researches of Holetschek indicate that these 

 are different bodies. 



D' Arrest's comet was found by Tempel, of Florence, in 

 the place indicated by Le Veau's ephemeris. 



Comet e was discovered by Coggia, September 13, and/" 

 by Tempel, October 2. 



In regard to comet b, 1877 (Winnecke's), the discoverer 

 has remarked that a similarity exists between its elements 

 and those of comets II. 1827 and II. 1852. The intervals 

 1827-52 and 1852-77 being equal (twenty-five years) lends 

 additional strength to the supposition of identity. This 

 question is remarked upon by Hind in Nature (April 19), 

 w 7 ho says: "The case is a very curious one, and possibly 

 unique of its kind : similarity of elements at three epochs 

 separated by very nearly equal intervals; and on the as- 

 sumption of a corresponding period of revolution, a very 

 near apparent approach to the planet {Jupiter) which so 

 greatly disturbs the cometary orbits ; yet action to account 

 for outstanding: differences of elements could not have taken 

 place on either occasion of the comet's passage through that 

 part of the orbit where great perturbation would be looked 

 for." 



B 



