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demonstrable that a very small proportion only of the shooting-stars which become visible to us, can escape from the earth's atmosphere. The result is of course that they must reach the earth, probably in a dispersed and divided state. It seems to us indeed not wholly improbable that some of those elements which the lightning-spectrum shows to exist in the atmosphere, may be due to the perpetual dissipation and precipitation of the substance of shooting-stars.

The remarkable discovery lately made, that the great November star-stream travels in the track of a telescopic comet (whose period is 334 years), that the August strean, in like manner, follows the track of the great comet of 1862 (whose period is 142 years), and that other noted shooting-star systems show a similar relation to the paths of other comets, opens out the most startling views of the manner in which cosmical space—or at least that part of space over which the sun's attractive power bears sway—is occupied by myriads on myriads of bodies more or less minute. If those comets—not one in fifty even of discovered comets—whose orbits approach that of the earth, are attended by such important streams of cosmic matter: if, for instance, the minute telescopic comet (known as I., 1866), in whose track the November meteors travel, is attended by a train capable of producing magnificent star-showers for nine hundred centuries—what multitudes of minute planets must be supposed to exist in the complete cometary system !

The Cornhill Magazine for November, 1867.

173

METEORS AND METEOR SYSTEMS.

One of the most remarkable features in the history of scientific progress has been the slowness with which the full significance of important discoveries has been recognised even by the professed students of science. When a great discovery is made, one can understand that some delay should occur before the newly learned fact is accepted as a recognised truth ; but when some great new truth has been admitted on all hands, it might be supposed that all the consequences which follow from that truth would at once be accepted; or rather that the students of science would vie with each other in pushing the search for such results to its utmost legitimate limits.

This, however, seldom happens. Whether it is that a discovery effected by another is regarded as not presenting an inviting subject of study and contemplation; or whether it is that men are ready to hope more from their own original researches than from work devoted to the investigation of the discoveries of others; or whether, lastly (but surely this cannot be the true interpretation), it is feared that all credit for results obtained by studying a truth discovered by another will be assigned to him—it is certain that we very seldom find the students of science willing to analyse

the results obtained by other men. There are of course exceptions, and noble exceptions. The investigation by the Continental mathematicians of the results flowing from the law of gravity, the study by spectroscopists of the results flowing from Kirchoff's great discovery, and some other cases may be cited. But unless a new truth is, as in these instances, of a very striking and even imposing nature, it is left very much to itself, and only by slow degrees are its fruits gathered in.

The discoveries recently made by Schiaparelli, Adams, and others, respecting the bodies called meteors (under which name may be conveniently included shooting-stars, aërolites, bolides, and the like), afford a very apt illustration of the peculiarity I have referred to. The consequences which flow directly from these discoveries, and still more those which may be legitimately deduced from them by careful reasoning, are full of interest, and bear in a most important manner on the economy of the solar system ; nay, it needs but a moderate study of the subject to see that questions affecting even the relations of the interplanetary spaces are suggested by the discoveries which have recently been made respecting meteors and their motions. Yet but few among modern astronomers have been willing to make researches into these matters. Professors Herschel and Newcombe, Mr. Stoney, Sir John Herschel, and a few others, have dealt with the subject; but the great body of astronomers would seem almost to have forgotten that

Schiaparelli and Adams had made any important discoveries at all in this matter.

I propose briefly to describe the discoveries referred to, and then to consider some of the conclusions which may be deduced from them.

Less than ten years ago a comparatively insignificant position was assigned to meteors, regarded as members of the solar system. It was but recently, indeed, that these bodies had come to be looked upon as belonging to the solar system at all. From being regarded as a species of exhalations consumed during some sudden processes of change in the upper region of air, they had risen to the rank of volcanic missiles from the moon. Next, the occurrence of meteoric showers at certain definite times of the year—that is, as the earth traverses certain definite parts of her orbit—had compelled astronomers to recognise the fact that meteor systems must exist, which regarded as systems occupy a relatively fixed position in the solar system. The individual meteors may or rather must be in swift motion ; and if a meteor system includes a swarm of meteors, then that swarm must also be in swift motion : but regarding the system as a whole, it must have the same sort of relative fixity which the earth's orbit itself has. Otherwise the occurrence of annual showers would remain unaccounted for; since we require that near a certain point the earth's path should be crossed or closely approached by the track of the meteors belonging to a system-and that not for a single year, but for many years or even centuries in succession.

Now, directing their search to other parts of the solar system, astronomers presently found what they took to be the analogue of the meteor families traversed by the earth. The zone of asteroids consists of a number of relatively minute bodies travelling around the sun. Distinct in all its characteristics from the family of smaller planets circling close by his globe, and equally distinct from the moon-attended family of outer planets, the asteroidal zone may be regarded as forming a family apart. Now, we do not know how many members there may be in this family, nor do we know what may be the extreme limits of its range, either outwards towards the family of major planets, or inwards towards the terrestrial family of planets. But what we know respecting it teaches us to infer that if all the asteroidal orbits could be seen as rings of light around the sun from some distant station, the combined system of rings would form a ring system whose densest portion would appear as a nearly circular and somewhat flat zone between the orbits of Mars and Jupiter, and close to the plane of the ecliptic. And we have only to conceive the case of a large planet circling around the sun along the thick part of this ring to see that results analogous to those presented as the earth circles amidst the imagined meteor systems would inevitably follow.

Hence astronomers inferred that a number of meteor systems travelling in orbits of no considerable eccentricity occupy the region through which the earth's orbit passes. The boldest reasoned that, in all probability, the whole space between the earth's orbit and

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