Historical Facts.
1. Seneca informs us that Ephoras, a Greek writer of the fourth century before Christ had recorded the singular fact of a comet's separation into two distinct parts.[13] This statement was deemed incredible by the Roman philosopher, inasmuch as the occurrence was then without a parallel. More recent observations of similar phenomena leave no room to question the historian's veracity.
2. The head of the great comet of A.D. 389, according to the writers of that period, was "composed of several small stars." (Hind's "Comets," p. 103.)
3. On June 27, A.D. 416, two comets appeared in the constellation Hercules, and pursued nearly the same apparent path. Probably at a former epoch the pair had constituted a single comet.[14]
4. On August 4, 813, "a comet was seen which resembled two moons joined together." They subsequently separated, the fragments assuming different forms.[15]
5. The Chinese annals record the appearance of three comets—one large and two smaller ones—at the same time, in the year 896 of our era. "They traveled together for three days. The little ones disappeared first, and then the large one."[16] The bodies were probably fragments of a large comet which, on approaching the sun, had been separated into parts a short time previous to the date of their discovery.
6. The third comet of 1618.—The great comet of 1618 exhibited decided symptoms of disintegration. When first observed (on November 30), its appearance was that of a lucid and nearly spherical mass. On the eighth day the process of division was distinctly noticed, and on the 20th of December it resembled a cluster of small stars.[17]
7. The comet of 1661.—The elements of the comets of 1532 and 1661 have a remarkable resemblance, and previous to the year 1790 astronomers regarded the bodies as identical. The similarity of the elements is seen at a glance in the following table:
| Comet of 1532. | Comet of 1661. | |||
| 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.