made in our northern hemisphere, is is easily reconciled with the modern theory, when we consider that the north pole is on the forward hemisphere of the earth (considered with reference to her orbital motion) during the first-named period, and on the rear (or sheltered) hemisphere during the second.

Again, it has been remarked that shooting-stars are seen more commonly in the hours after midnight, and that aërolites fall more commonly before noon. In other words, these extraneous bodies reach the earth (or her atmosphere) more frequently in the hours from midnight to noon than in those from noon to midnight. Humboldt suggests in explanation we know not what theory of variation in the ignition-powers of different hours. But it is clear that the true explanation is founded on the principle presented in the preceding paragraph, since the forward hemisphere contains places whose local time lies, roughly speaking, between midnight and noon, while places whose local hour lies between noon and midnight lie on the sheltered hemisphere.

If we remember that the earth is but a point in space, we may fairly conclude that the number of bodies composing meteor-zones is all but infinite. Large, therefore, as the numbers of these bodies which fall on the earth may be, there is no reason to suppose (perhaps if we knew the true functions of these bodies, we might say-there is no reason to fear) that the supply of meteors will ever be perceptibly diminished. Although the contrary opinion is often expressed, it is

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 me 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 33 years), that the August stream, 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 years what multitudes of minute planets must be supposed to exist in the complete cometary system!

:

The Cornhill Magazine for November 1867.

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

There are of

the results obtained by other men. 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 Kirchhoff'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 Newton, 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.

Not many 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 this not for a single year, but for many years or even centuries in succession.