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respecting meteors during this last four or occupy more space than can here be
The first, and in some respects the most striking feature, of the new meteoric astronomy, is the amazing extent of the paths on which meteors travel. There was something very startling in the conclusion to which astronomers had been already led, that meteors are bodies which, before encountering our earth, have travelled on paths comparable in extent with hers. That a tiny body - a body so light, in many instances, that a child could play with it should for countless ages have swept around the sun on a path many millions of miles in diameter; that in fact, such a body should have been in reality a planet, was certainly a most surprising theory. But now we know that, so far as orbital range is concerned, our earth sinks into utter insignificance beside most, if not all, We do not purpose here to trace out of these meteoric bodies. Astronomers have the progress of those labours by which only been able to determine the real paths our present knowledge of the nature of of two meteoric systems; but these two meteors and of the part they play in the systems afford very significant evidence economy of the solar system has been respecting their fellow-systems. The memgained. The history of those researches bers of one- the November system is full of interest, not only on account of travel to a distance exceeding that at the strangeness of the facts to which as- which remote Uranus pursues his gloomy tronomers have been led, but also ou ac- career; the members of the other - the count of the singular coincidences which August family of meteors pass to a dishave marked the progress of inquiry. At tance far exceeding even that of Neptune. one time, it is a great display of shooting-As it is wholly unlikely that the two mestars which takes place just as astrono- teor systems first successfully dealt with mers required special information respect- are the most extended of all those which ing meteoric showers; at another, a bright the earth encounters, the conclusion may comet the only comet of the 650 hither- fairly be accepted that there are meteor to detected which could give certain in- systems whose members travel to distances formation appears at the very time exceeding even the enormous range of the when the information was needed; and at August meteors. yet another, precisely when astronomers were inquiring about another comet supposed to have escaped detection (if it had, indeed, any real existence), they find that that very comet had been seen, its path calculated, and even its constitution determined only a few months before. Such coincidences as these, the assiduity displayed by Adams, Leverrier, and their fellow-workers, and the singular conclusions to which their labours point, undoubtedly cause the account of the last few years of meteoric research to form one of the most interesting chapters in the history of astronomy. But the narrative of these matters has been given elsewhere, and is doubtless already familiar to most of those who will read these pages. It would also VOL. XXIV. 1113
But there is evidence of meteoric ranges compared with which the distances just referred to are literally as nothing. It is in considering such ranges, as we shall presently see, that we touch on the question of seedbearing meteors.
When as yet astronomers had no proof that any meteors travel on such wide paths as we have mentioned, no great reliance was placed upon the estimates of meteoric velocities, as deduced from actual observation. The acknowledged difficulty of the task of observation, and some seeming discrepancies in the results, were held sufficient reasons for regarding those estimates as unreliable. For if the estimates were accepted, some very startling conclusions had to be accepted with them.
But even this explanation is insufficient. It must be accepted as true so far as it
Let it be remembered that a body which We should be compelled to believe in mecrosses the earth's track cannot possibly teoric voyages, compared with which the have a velocity exceeding a certain defi- journeys of the August and November menite amount, if it has reached the earth's teors would be altogether insignificant. course under the sole influence of the sun's We should have to regard some at least of attraction. If the sun draw in meteors the meteors which our earth encounters as from surrounding space, then every one of bodies which had traversed the inconceivthose meteors will show by its rate of mo- able distances separating our solar system tion that it has been gathered in by the from the stars. And the wonder would sun's might as a ruler of matter. The be enhanced by the consideration that a planets, indeed, may help the sun to some million of years would be insufficient for small extent; but as a rule we may leave the least of those tremendous voyages. their influence out of consideration so far as the meteoric velocities are concerned. What opinion, however, are we to form if extends. Those meteors which enter the any meteors show a rate of motion exceed-earthly atmosphere with the velocities ing that which the sun can impart to spoken of must have come from extra-solar them? If observers, having carefully space; they must be visitants from the dowatched a meteor's fiery course from two main of other suns. This is as certain as stations, deduced by calculations of a sim- the conclusions of astronomers respecting ple and convincing kind, a rate of motion the past and future motions of the planets which is greater than that due to solar themselves. But this stupendous fact attraction, where are we to find the "pow-leaves the vast velocities of the meteors er" which has caused the meteor to travel still unexplained. And for this simple with that extra velocity? reason: Though Sirius and Arcturus certainly, and many other stars probably, are capable of giving to meteors travelling towards them velocities which far exceed those which our sun can impart, yet the velocities those mighty orbs impart they also take away. Conceive for a moment the case of a meteoric body at rest in space, and about as far from Sirius as the nearest fixed star is from the sun. Sirius would draw that body towards himself, at first slowly, and afterwards more quickly, and in the course of about a hundred thousand years the body would be urging its way with inconceivable velocity amidst the planetary domain ruled over by that glorious sun. We can conceive that it would be so far disturbed on its course as not to plunge straight upon the surface of Sirius (as it would certainly do if undisturbed), but that, wheeling at its highest speed close around his mighty globe, it would pass away precisely as a comet passes away from our sun after circling closely round him. At the moment of nearest approach the body would travel at the rate of about five thousand miles per second (at a moderate computation), and this velocity is far greater than any possessed by meteors which approach our own sun. But as the meteor swept away from Sirius, the same surpassing might which had given to the meteor this amazing velocity would continually reduce the meteor's speed. The reduction of speed in retreat would correspond exactly with the acquisition of speed in approach; and when at length the meteor had reached its original
Now the most careful observations of meteoric movements do actually show, in many instances, a rate of motion exceeding by many miles per second that which astronomers can fairly account for. Our earth moves at the rate of eighteen miles per second, and a meteor drawn in by the sun's might from a distance exceeding even stellar distances would cross the earth's track at the rate of about twentysix miles per second. Supposing the meteor to meet the earth full tilt, there would result but a velocity of forty-four miles per second, for the earth's attraction on the meteor would not appreciably increase its velocity. But careful observers tell us that some meteors travel through the air at the rate of sixty, or even seventy or eighty, miles per second. The extra velocity is a peculiarity too well supported by the evidence to be neglected. An explanation must undoubtedly be sought for. But whence is this explanation to be obtained? There are other bodies in the universe which exert a mightier attraction than our sun, and are, therefore, capable of imparting greater velocities. The star Sirius, for example, must force those meteoric bodies which circle around it to travel at a rate exceeding more than tenfold, at the very least, the velocities imparted to meteors by our sun's influence. It might seem, then, that we need only look to the larger stars to those suns, that is, which are more massive than our own sun for the source of these perplexing meteoric velocities. This would be sufficiently amazing.
Still there are two explanations which seem to be available, though one only, as we judge, is of itself sufficient to account for the peculiarity we are considering. Probably both must in any case be ad
distance, although it would not be reduced | verse, has set the excessive velocities of strictly to rest at first, yet the motion it some meteors among the mysteries of the would possess (due solely to the disturb- Cosmos; and that, so far as we are aware, ing action exerted upon it while travers- no explanation has ever been given of the ing the Sirian planetary scheme) would be phenomenon. slower than the motion of the inost sluggish river. It could never carry to other systems any appreciable portion of the velocity it had acquired while traversing the system of which Sirius is the ruling centre. Our difficulty remains, then, still unex-mitted. plained. But before searching anew for The first relates to a fact which is itself an explanation, we may note another very among the most amazing with which ascurious inference from what has already tronomers have to deal. All the stars are been shown. We have seen that meteoric in rapid motion, though seemingly fixed. bodies which travel with such enormous Amidst those depths where all appears at velocities as have been noted in some in- rest motions are taking place which are so stances, must certainly have come from rapid that the mind is utterly unable to the domain of another sun than ours. But conceive them. Masses millions of times precisely as meteors approach our sun, and then pass away for ever, so meteors that come to us from the domain of other stars must, in many instances, have passed into those domains from the domains of yet other stars. Nor can it be regarded as likely in the nature of things that only some two or three such voyages have been performed. On the contrary, it must be regarded as almost certain that, in some cases, meteors traverse inter-stellar spaces many hundreds of times, visiting each time a different stellar domain,-and perhaps even completing more than one cir-moon were at perfect rest. So that the cuit around some stars. Remembering that the least interval in which a body can pass from the domain of one star to that of another is about a million of years, we begin to recognize the wonderful antiquity of many of those bodies which have been thought fit emblems of all that is transient and perishable.
larger than our earth are urging their swift career through space with velocities compared with which all the forms of motion with which we are familiar are as absolute rest. Now, it is a well-known law of motion that each kind of movement possessed by a body takes place independently of all the others. The moon circles round the earth as if the earth were not circling round the sun. A body would circle round the moon while she circles round the earth (and with the earth around the sun), precisely as though the
motions of the bodies dependent on any star take place quite independently of the motion by which the star is sweeping amid the depths of the star-system. Our earth, for instance, pursues her course round the sun as steadily as though the sun were at rest, instead of being in rapid motion with all his cortège of planets. And the power which a star has of communicating velocity to an approaching dependent body, and of withdrawing velocity from a receding body, has no reference to the motion which the body shares with the star. Take the case of Sirius, for instance. In what we said of him above we regarded him as at rest; and we stated, justly, that he could communicate to a body approaching him from a state of rest an enormous velocity, the whole of which he would withdraw during the recession of the body. But Sirius is, in reality, travelling with great velocity amid the star-depths; and if we conceive the case of a meteoric body circling close around Sirius with the enormous velocity already referred to, we must remember further that that body shares Let us premise that Dr. Mayer, in his also with Sirius the great velocity wherecelebrated inquiry into the part which with the star is being carried through meteors play in the economy of the uni-'space. The first velocity Sirius has him
But it is when we seek for an explanation of the excess of velocity that we are led to the most startling conclusion. Let it be remembered that this excess of velocity is now regarded by astronomers as a real fact, because the observations which had been considered as doubtful have been confirmed by what has been proved respecting certain meteoric systems. There is such a perfect accordance between the estimated and the actual speed with which the August and November meteors pass through our atmosphere that estimates of the yet higher velocities with which some meteors move cannot be looked on with suspicion. We shall presently see also that there are independent reasons for believing in these amazing velocities.
self communicated, and he not only can, but will, withdraw it wholly from the meteor; but the other velocity he has not imparted, and neither can he withdraw it. The meteor will pass away, and will be reduced to all but rest with respect to Sirius, that is, to a condition in which it neither approaches nor recedes from the star; but this very state of rest with respect to Sirius implies an enormous velocity with respect to space. Precisely as a body at rest on Sirius, or within his mass, is being carried at the rate of some thirty miles per second through space, so would our meteor possess this enormous real velocity, though reduced to all but absolute rest with respect to Sirius.
Now, bodies passing from the domain of one star to that of another must carry with them this balance of motion which their late ruler has been unable to touch. The effect will be different according to the manner in which they enter the domain of their new ruler; but it may happen in many cases that they will appear to move with the whole of this velocity as an excess of motion over and above that due to the sway of the star ruling them for the time being.
because acting in different directions. But supposing all these stars removed to one side of the first, so as to combine their attractions upon it, even then, at the enormous real distances separating the stars from each other, the resulting motions would not be comparable with those which actually exist. Thus we have, in the motions of the fixed stars, the evidence of a mighty force other (it would seem) than gravity, and perhaps acting according to other laws.
Now, if the assumed explanation of the rapid motions of meteors be correct, these bodies bring before us, in the most direct possible manner, the effects of this mighty force. They penetrate the atmosphere of our earth with velocities generated either by attracting bodies - non-luminous stars for instance - other than those we are cognizant of, or else by forms of force distinct from the attraction of gravity. Here, then, we have a conception respecting these bodies which is even more startling than the conception that they may be fragments of an exploded world, or that they may bear with them the germs of life. It is true that we know of no instance in which a world has exploded, for astronomers no longer imagine that the asteroids are fragments of a world which once travelled between the paths of Mars and Jupiter; nor is it very easy to conceive how the germs of living things can be preserved under the conditions to which meteors are subject. But volcanic action shows us at It is, in the first place, a surprising cir- least how worlds might be supposed to cumstance that the stars should travel so explode; for we commonly compare a volswiftly as they do, amid the depths of cano to a safety-valve, and the purpose of space. We do not here speak of this a safety-valve is to prevent explosion. circumstance as surprising merely in the And, again, the idea of the conveyance sense in which so many astronomical facts of the germs of life from place to place is are surprising. It is startling to consider one with which we are sufficiently familiar. that Sirius is more than a thousand times | But in the motions of the meteors we have more massive than our sun, or that the evidence either of the existence of bodies sun is more than a million times larger differing from all with which we are acthan the earth on which we live. But quainted, - more massive than the suns, there is nothing in these or similar facts, but as opaque as the planets, or else of which is not in accordance with our ideas the action of a force mightier than the respecting the constitution of the universe. force of gravity. In the rapid motions of the stars, however, there is a source of grave perplexity, in the circumstance that motion is a measure of force, and we cannot understand what the force can be which has produced these motions. The mutual attractions of the stars are utterly unequal to the generation of velocities so enormous. The stars which are the next neighbours of any tions are large enough to avail for our given star are those which tend most purpose. Sirius has a rate of motion altoeffectually to excite motion in that star; gether exceptional; and it is probable that and their attractions counteract each other the average rate of stellar motion does not
At first sight, it seems as though we have here a sufficient explanation of the peculiarity we are considering. It will presently be shown that some difficulties still remain. But before passing on, let us consider the strange explanation we have been dealing with.
While we may admit, however, that in many instances the great velocities of meteoric bodies may be due to the proper motions of those stars from whose domains the meteors have reached our earth, yet it is difficult to regard this explanation as altogether sufficient. In the first place, there are few stars whose mo
exceed four or five miles per second. And again, only a smaller proportion of the meteoric bodies coming from the domain of one star to that of another would show traces of the kind of motion we have been considering. Certainly very few would show an excess of velocity corresponding to the rate of seventy or eighty miles per second, with which meteors have been observed to traverse our atmosphere.
The second explanation is this: that a large proportion of our meteoric visitants have been expelled or erupted from the stars-including our own sun.
that a velocity fully as great as that which we have spoken, of may be imparted to matter expelled from the sun's substance. It is generally admitted that the prominences are due to some eruptive, or at least repulsive force exerted by the sun. They have been seen to form like jets from a fountain, rushing forth with incredible velocity till they have attained their greatest height, and then falling back, more or The second explanation of which we less rapidly, towards the sun's surface. have spoken seems required, to interpret Now estimates have been formed respectwhat still remains unaccounted for. This ing their velocity by direct observation, explanation is so startling, that at first the powers of the spectroscope availing sight few would be disposed to admit it as for this purpose. But we have in the even a possibility. However, when the height to which these prominences attain ories so surprising as Sir W. Thomson's the most satisfactory evidence of the hypothesis of seedbearing meteorites are velocity with which the gas comprising submitted to the gravest scientific assem- them has been propelled from the sun's blies, we need not fear to present even so interior. Assuming only that the promstartling a theory as the one we are about inences are formed of projected matter, to deal with, more especially as we shall we can as certainly determine the rate of be able to exhibit very singular evidences propulsion as we can determine at what in its favour. rate a cannon-ball must be propelled vertically upwards from the earth's surface to reach a given height. At least, we can determine the lowest velocity which would suffice, supposing we see the full height of the prominences, and nothing happens to check the upward motion of their gaseous substance. But as surely as we know that a cannon-ball must be fired at a much higher velocity to attain a given height through the air than would suffice if it could be fired in a vacuum, so also we can infer that whatever velocity we deduce from the prominence matter, regarding it as projected through vacant space, must fall very far short of the real velocity. May we not even go farther; and consider rather the velocity with which the smoke leaves the mouth of the cannon as compared with that necessary to carry a projectile only to the height reached by the smoke? If we accept this view, and certainly the constitution of the prominences favours the supposition, we should decide that there can be scarcely any comparison between the velocity with which the matter of the prominences is projected from the sun's interior and that which would carry a projectile in a vacuum to the observed height of the prominences.
The most obvious objection to this hypothesis resides in the fact that what appears an utterly incredible velocity must be communicated to the expelled matter in order to render the explanation available. It is necessary that the stellar volcanoes should propel meteoric matter from their interior with a velocity sufficient to free the missels for ever thereafter from the control of their parent star. Now, to take the case of our own sun, any matter shot forth from his interior at a rate of less than 380 miles per second would return to him again under the influence of his far-reaching attraction. It would, if undisturbed by planetary attraction, return (after a long excursion) in such sort as to strike his surface as squarely as it had left that surface. But even taking into account all disturbing forces, it would still return to the sun. A velocity exceeding that just named would free the erupted matter from the sun's influence, to this extent at least, that though the sun would continually retard the motion of the receding matter, he would never be able to destroy that motion or change it into a motion of approach. But it seems incredible that any forces residing in the sun should be competent to propel matter from his globe
at a rate so enormous.
And yet the evidence obtained during the past few years respecting the motion of the solar prominences seems to show
Now the largest prominence yet seen had the enormous height of 160,000 miles; and a projectile from the sun would require a velocity of 200 miles per second at starting, to attain, even through vacant space, to this vast height. It will scarcely be thought too daring to assert that the matter of this prominence must have had