Longitude of perihelion 111° 48´ 115° 16´ Longitude of ascending node 87 23 81 54 Inclination 32 36 33 1 Perihelion distance 0.5192 0.4427 Motion Direct. Direct. The elements of the former are by Olbers; those of the latter by Mechain. The return of the comet about 1790, though generally expected, was looked for in vain. As a possible explanation of this fact, it is interesting to recur to an almost forgotten statement of Hevelius. This astronomer observed in the comet of 1661 an apparent breaking up of the body into separate fragments.[18] The case may be analogous to that of Biela's comet. [18] "Cometographia," p. 417. 8. The identity of the comets of 1866 and 1366, first suggested by Professor H. A. Newton, is now unquestioned. The existence then of a meteoric swarm, moving in the same track, is not the only evidence of the original comet's partial dissolution. The comet of 1866 was invisible to the naked eye; that of 1366, seen under nearly similar circumstances, was a conspicuous object. The statement of the Chinese historian that "it appeared nearly as large as a tow measure,"[19] though somewhat indefinite, certainly justifies the conclusion that its magnitude has greatly diminished during the last 500 years. The meteors moving in the same orbit are doubtless the products of this gradual separation. [19] Williams' "Chinese Observations of Comets," p. 73. 9. The repartition of Biela's comet in 1845, as well as the non-appearance of the two fragments in 1865 and 1872,[20] were referred to in a previous chapter. [20] One of the parts was seen at Madras, India, on the mornings of December 2 and 3, 1872. The comet of Halley, if we may credit the descriptions given by ancient writers, has been decreasing in brilliancy from age to age. The same is true in regard to several others believed to be periodic. The comet of A.D. 1097 had a tail 50° long. At its return, in March, 1840, the length of its tail was only 5°. The third comet of 1790 and the first of 1825 are supposed, from the similarity of their elements, to be identical. Each perihelion passage occurred in May, yet the tail at the former appearance was 4° in length, at the latter but 2-1/2°. Other instances might be specified of this apparent gradual dissolution. It would seem, indeed, extremely improbable that the particles driven off from comets in their approach to the sun, forming tails extending millions of miles from the principal mass, should again be collected around the same nuclei.