how two distinct tails might be expelled or repelled from a single head; but it is not so easy to see how two complete comets could be formed out of one in this way, nothing apparently remaining. To make clear the nature of this reasoning, I remind the reader that a comet's tail is either formed out of the head (according to Sir J. Herschel's theory), or else is formed through a certain action exerted by the head (according to Prof. Tyndall's). In the former case, the process never (so far as observation extends) results in completely using up the head; in the latter, very obviously, the head must remain, or the action would cease. In either case, then, the head would remain. So that when two tails were formed they would extend from one and the same head. The head cannot be made double by the same process which produces the double tail. There must be some distinct action on the head to produce such a result. Now the tails, after they are formed, might have the power of drawing away each its own share of the original head; but the supposition seems rather a wild one. On the contrary, the supposition that the comet may have divided upon a meteoric group involves nothing which is not in accordance with known facts, since such meteoric groups exist in countless numbers within the interplanetary spaces.

It is certainly unsafe, however, to dogmatise upon this difficult subject in the present state of our knowledge.

Whatever may have been the cause of this comet's dissipation, it would seem to admit of no possibility of question that the comet has been finally and completely

removed from the list of existing comets. Of course, it has not been absolutely destroyed; its fragments exist somewhere but, as a comet, it has ceased to exist. If it had continued unchanged, it would have been again in view, and on the whole under favourable circumstances, during October in the present year (1872). Prepared to find it much fainter than of yore, or its fragments more widely dispersed, astronomers searched for it with more care than in 1866, not only using more powerful instruments, but extending their search over a wider range. But the comet was not found. At the next return, its path would bring it too near to the sun for astronomers to observe it, even though it retained its original brightness. We may assume that the process of dissipation and dispersion has been all this time in progress. And therefore it is impossible to hope that a trace of the comet will be recognised in 1880,-when it would again have passed into view but for the misfortunes which have befallen it.

This being the case, my readers perhaps will be surprised to hear that in a few days from the appearance of these lines (Nov. 1, 1872), astronomers expect to see certain fragments of debris of this very comet. This, however, is actually the case. Since the year 1798, there have appeared from time to time, early in December, certain meteors or falling stars which follow a track closely according with the path of Biela's comet. There is not a perfect agreement; but Dr Weiss, a German astronomer, has shewn that the actual path of the meteors corresponds almost perfectly with that of a comet which appeared in 1818, and which there is

now excellent reason for regarding as itself a fragment of Biela's comet. Now, between November 25 and December 5, the earth will be passing through the broad tracks of both these comets, or-regarding Biela's as two-through the tracks of these three comets, and so closely behind Biela's pair, that we may fairly expect to see many meteors during that week. Precisely as, in November 1866, there was a splendid display of November meteors, following on the track of Tempel's comet (which had passed early in 1866), so this year there will probably be a display of meteors following the track of Biela's comet, which, though unseen, must have crossed the earth's path about the middle of October. At any rate, the skies should be carefully watched. The shower of meteors (should any occur) will fall in such a direction that shooting-stars might be looked for at any hour of the night. And those belonging to Biela's comet could be very readily distinguished from others, because their tracks would seem to radiate from the constellation Cassiopeia. So that should any of my readers observe, on any night between November 25 and December 5, a shooting-star following such a track, he will have the satisfaction of knowing that in all probability he has seen a fragment or follower of a comet which has divided into two if not three distinct comets, and has followed up that process of dissipation by dissolving altogether away.

It is not easy to form an opinion as to the actual probability that a fine display of meteors will be seen. This particular meteor system has, however, been known to

produce somewhat remarkable showers. Thus Brandes, who first recognised the existence of the system, counted no less than four hundred meteors in a few hours, while travelling in a covered carriage on the night of December 7, 1798.

In conclusion, we may draw, I think, from the history of the missing comet the inference that our earth and her fellow-planets have little to fear from collision with comets. The earth passes each year through more than a hundred meteor systems and yet suffers no injury, whereas Biela's comet would seem to have been destroyed during only a few encounters with meteoric groups. It appears evident, then, that it would be the comet, not our earth, which would suffer in any encounter of the sort. Indeed, comets, which once occasioned such dread, seem to be but frail creatures. To quote the words of poor Blanqui, the republican, who wrote in prison about comets as if he sympathised with them in their trials,—" if comets escape Saturn, it is to fall under the stroke of Jupiter, the policeman of the solar system. On duty in the dark, he scents (sic) these hairy nothings (nihilités chevelues), before a ray makes them visible, and urges them-distracted-towards perilous passes. There, seized by heat and swollen to monstrosity, they lose their shape, lengthen, disaggregate, and break confusedly through the terrible straits, abandoning the stragglers everywhere, and only managing to regain, with great difficulty, under the protection of cold, their unknown solitudes."

THE LOST COMET AND ITS METEOR-TRAIN.

THE meteor-shower which occurred on November 27, 1872, and the circumstances connected with that event, not only attracted a fresh interest to the subject of meteoric astronomy, but afforded important evidence respecting the connection which undoubtedly exists between meteors and comets. I propose in this paper to consider more particularly the events referred to, having already in the last essay but one dealt with the history of meteoric and cometic astronomy.

It has been shown by the labours of Schiaparelli, Adams, Peters, Tempel, and other astronomers, that the meteors of November 13-14 (called the Leonides) travel in the track of Tempel's comet. The meteors of August 10-11, or Perseides, have also been shown to travel in the track of a comet. Other such instances of association have been more or less fully recognised; and now the conclusion has been generally accepted, that in the train or path of comets bodies travel in scattered flights, which, if they fall on the atmosphere of the earth, appear as shooting-stars or meteors.

Until the recent shower, however, the inquiries made in this branch of research had been limited to cases of