Page:The story of the comets.djvu/134

94 been seen since. Bearing in mind its size and brilliancy (unusual for a short-period comet), its non-appearance since 1844 is a remarkable fact, and one as to which no assured explanation can be given. Some computations by Le Verrier seemed to render probable that Di Vico's Comet was identical with the comet of 1678, and several other identifications have been suggested, but there is no certainty about any of them. It is, however, worth mentioning that the elements of Finlay's Comet (1886, vii.) closely resemble those assigned to Di Vico's Comet by Brünnow; but the resemblance appears to be fortuitous: that is to say that they are two distinct comets moving in orbits similar in many respects but not in all.

On Nov. 20, 1894, E. Swift in California discovered a small comet, the elements of whose orbit closely resemble the elements assigned to Di Vico's Comet; and Schulhof and others are strongly impressed with the idea that the 2 objects are identical. Future years may help to clear up the matter. Should the question be decisively settled in the affirmative, we must assume that the comet is subject to marked changes of brilliancy. This comet was not seen either in the autumn of 1900, nor in July, 1907, when it was expected; and it must be regarded as "lost", unless it should be found in Dec. 1912. Its period has been put at 6⋅4 years.

This chapter may be suitably brought to a close by recording, without entering into much detail, certain comets to which short periods have been assigned, but as to which our knowledge remains too imperfect for much to be said. These comets are the following:—