Chief amongst the mysterious comets must be ranked that which goes by the name of Biela. This comet, first seen in 1772, was afterwards found to have a period of about 6¾ years, and on numerous occasions it reappeared at intervals of that length down to 1845, when the mysterious part of its career seems to have commenced. In December of that year this comet threw off a fragment of nearly the same shape as itself, and the two portions travelled together side by side for four months, the distance between the fragments slowly increasing. At the end of the four months in question the comet passed out of sight owing to the distance from the earth to which it had attained. The comet returned again to perihelion in 1852, remaining visible for three weeks. The two portions of the comet noticed in 1846 retained their individuality in 1852, but the distance between them had increased to about eight times the greatest distance noticed in 1846. As a comet Biela’s Comet has never been seen since 1852, and it must now be regarded as having permanently disappeared. But what seems to have happened is this, that Biela’s Comet has become broken up into a mass of meteors. On November 27, 1872, and again in November 1885, when the earth in travelling along its own orbit reached a certain point where its orbit intersected the former orbit of Biela’s Comet the Earth encountered, instead of the comet which ought to have been there, a wonderful mass of meteors; and it is now generally accepted that these meteors, which apparently are keeping more or less together as a fairly compact swarm, are nought else than the disintegrated materials of what once was Biela’s Comet. [Illustration: Fig. 26.—Biela’s Comet, February 19, 1846.]