Origin of Comets and meteors.

Te Aroha News, Volume IV, Issue 165, 14 August 1886, Page 8

Origin of Comets and meteors.

By Richard A. !PK,t]sitfß. t

1 i«MMM«MOT t t On Nov. 27, 1872,' the meteors following after Biela's comet were seen in tens of thousands, as predicted. A few were seen in 1879, on Nov. 28 And on Friday, Nov. « 27 last, the display of Bielan meteors announced by me in the " Times " as likely to occur took- place as expected, and was witnessed all over Europe, No doubt can remain, I think, in any reasoning mind that the connection of these meteors with the comet named after' Biela (which should properly be called O&mbart's comet, as Gambart first determined its path) has been amply established. We have, apart from the evidence already decisive, obtained by Olmsted, Schiaparelli, and Adams, the 1 following points:— A comet appears, whole, in 1826 ; returns, still whole, in 1832 ; returns, but is not seen, being unfavourably situated, in 1839 ; returns, still whole, in 1845 ; but early in 1846 divides into two; returns, still double, in 1852; may or may not have returned as a double, or perhaps multiple, comet in 1859, but would have been invisible, being unfavourably near the sun on the skies ; was not seen in 1866 iti any form, or as a comet in 1872, 1879, or 1885; but in each of theae three last-named years, when the earth passed through the comet's track, evidence was given by the appearance of falling stars that along that track meteors were travelling, in flights of many millions, far behind the parent comet. It is not merely the agreement as to the year and the day of the year, which enables us to associate the meteors with Biela's comet ; they were travelling in that direction, and in that direction alone, out of millions of possible directions, which corresponded with the motion of meteors travelling along the track of the comet. We have to add to this that evidence already regarded as overwhelmingly convincing had shown other comets to be similarly followed by meteoric trains ; that, in fact, so far as can be judged, it is in the nature of all comets to have such trains ; and that all meteorstreams are thus associated with comets (either whole or long since dissipated). No doubt, then, as to the connection between the Andromedes of Nov. 27 and 28 and Biela's comet can be reasonably enter tamed. The occasion seems a good one for touching on the remarkable nature of $he problem which meteors and comets, thus understood, present. The facts collected together are so significant that we might fairly expect them to suggest the true theory of comets and meteors as clearly as —to take an appropriate illustration— the meteors seen during some great display indicate by their intersecting paths the "radiant point "of the system. If we examine carefully what has been proved, and sift carefully the theories which have seemed to be established, accepting such parts ©f theories as really have been established and suspending judgment as to what still remains doubtful, we shall find a singularly suggestive body of evidence in favour of a general theory which, viewed apart from such collected evidence, would appear surprising— nay, even startling — in character. We require at starting only the following two assumptions— which may be regarded as altogether reasonable -.—First, that what has been proved about comets generally may be regarded as true about meteor-systems ; and secondly, that what has been proved about meteors may be regarded as throwing light upon the nature of comets. Now, it has been shown by the researches of Stanislas Meunier, Tschermak, and others that among the meteorites which reach bur earth are bodies, ranging in structure from the asiderites (with very little iron) to the holosiderites (almost wholly iron), which are practically identical with volcanic products, ranging from the ultrabasic to the iron masses found at Ovifak, in Greenland — these last being so like the holosiderite meteors that they were long regarded as indubitably meteoric. It has further been shown that, on a careful investigation of all the evidence in regard to these meteorites and a discussion of the probabilities of their encounter with the earth on various theories as to their origin, it becomes almost a certainty that most of them not only are, as their structure shows, of volcanic origin, but were ejected originally from volcanoes on this very earth on which we live. Mr Ball, Astronomer Royal for Ireland, has discussed the evidence on thia point very soundly, thpugh, as will be seen, he does not carry the reasoning quite as far as it may be fairly taken. Every mass, small or great, ejected from the earth by volcanic action with a velocity exceeding seven miles per second would pass away on a path thenceforth carrying it round the sun, but crossing the earth's track at or near the point where the ejection took place. But for perturbations, the crossing-place would be alwayß at ' that very point; but perturbations would shift the place of crossing. Thus every meteorit mass so ejected would be 'exposed to the risk of recapture by the parent earth. On the contrary, the chance that a body ejected from any other planet whatsoever fall on the earth would be almost infinitesimally small. Thus, while a comparatively small amount of terrestrial ejections would serve to account for the considerable number of meteorites captured within historic times by the earth, we should have to imagine an almost infinitely large number of ejections from any other planet to account for so many captured meteorites (since for each one captured by the earth millions of millions must have been ej6cted -by that other planet if all of them came from it). So far we are on tolerably sure ground. Yetalreadywe have deducted a very surprising result. Nothing in the present activity of volcanoes ' would suggest an eruptive .power capable of ejecting matter with a velocity of seven miles per second, or more. Yet, remembering the evidence we have that the earth was once in a g'w.asa-surilike state, we can well believe that in her sunlike youth, ehe may from time to time have so concentrated • her volcanic energies as to expel matter even with tremendous velocities indicated by Ball's, ' or rather Tschermak's theory. Possibly, turning presently to a body .which actually is in a sunlike state, we may find evidence showing that this is the' way with sunlike orbs. Here Techermak and Ball pause. Content -with, showing^ that probably many millions of „meteoric bodies were ejected from our.pwn planet when she was a small sun, they, overlook the inference that what she could do the ; otber planets could presumably ,do also. ■ MV Ball, indeed, while admitting the possibility, of thi> in the .case of planets; no larger ,than, 'the earth, expresses the opinion, that the 1 giant planets could not expel volcanic products with the

m«ob> greater 'Velocitieatnecesaafv to..pyef-r copier thdtr jojwnfnjju'ph. greater j btjbractipris. He overlooks, apparently^tfeefcfr^umstaAc'ea that if much greater pgwer^ould be-re r quired, much • greater' power ' exiated. The/ vqlcahfc , energies'of ! a planet? .result from. the planet's internal heat," and the" intettial^: heat ia now recognisedas a direct product of the planet's '.gravity; It ' wouldv seem highly probable, then, if not certain', on a^ priori grounds alone, that the giant planets, would be able, like the;,earth, .to expel millions of millions of meteoric flights from their interior during their sunlike youth— possibly not yet altogether past. Turning next to direct evidence, we find that among the' multitudinous coments: belonging to our solar system can be recog; nised certain" families dependent on the giant planets in a somewhat peculiar 1 manner. Long before the , significance of, the feature had been noticed, I wrote of? " The Comet-families of the Giant Planets'** as a phenomenon needing to be inquired*' into. The comets thus classed into families: . travel around the sun as their rulingr centre , but with paths passing near* severally to the ■ track of one or other 'of the giant planets— Jupiter, Saturn, Uranus, or Neptune. Near, too, as > the approach is now, we may reasonably assume that this nearness of approach indicates actual intersection at some remote* time *n the past. The resemblance between this peculiarity, and the intersection of ; earth-ejected meteor-streams which the earth's orbit, according to the theory of Tschermak and the Astronomer Royal for Ireland, need ' hardly be insisted*:, on. If, as they consider almost certain, the meteor clouds vomited forth by the "■ earth in long-past ages became meteorstreams ' travelling round the sun, but always passing near the earth's orbit, then, the more important meteor clouds expelledby the giant planets would become moreimportant meteor systems travelling round* the sun, but ever thereafter passing near the track of the planets from which they had severally been expelled. And, in one case as in the other, the meteor stream would imply a comet, forwe have every reason to infer,, from what we know about meteors and: comets, that every meteor system is probably associated with a comet Indeed, two of the meteor systems actually identified aa - attendants on comets, follow severally in the tracks of comet belonging to the families' of the giant planets —the meteors of November 14 following in the tracks of Tempel'a* comet, which paesea the orbit of Uranus, and the meteors of November 27 following>.the track of Biela's comet, which passes very near the orbit of Jupiter. I am fully aware that another explanation — only one other seems even possible — hasbeen suggested for the strange way in which* comets and meteor systems cling around the orbits of the planets. This other explanation has even been sometimes described — though quite erroneously - as the accepted theory. It was advanced bySchiaparelli as an adjunct of the theory — > which really has been accepted, because demonstrated — that meteors and comets are associated. He suggested that the meteorsystems which now pass near the paths of the giant planets may have been drawn into the solar system by the perturbing action of those planets near which, on, their parabolic course around the sun, they chanced to pass. But while this explanation gives no account what, ever of the structure of meteoricbodies, it even fails to account for meteoric streams as we know them. It has been shown (with mathematical demonstration) that no flight of meteors could ever, bythe attractions of a giant planet, be so perturbed that all its members would thenceforth travel on practically the same orbit round the sun. Those passing nearest to> the disturbing planet would inevitably besent off on a different path from those which. were in the middle of the approaching flight, and these on a different path from, those farthest away, unless the flight were, very small indeed, in which caee its members would be kept together by their mutual attractions and no meteoric stream would be produced. ♦ On the other hand, the theory I have advanced, while itself suggested, and almostdemonstrated, by a priori evidence, explains perfectly the structure of meteors, and accounts for the eventual conversion of a flight of meteors (vomited forth in the form of a meteoric cloud in some immense eruption), into a meteoric stream. But we cannot stop here. There is a test which this theory, if sound, ought assuredly to bear. Ther6 are orbs actually in the sunlike stage —to wit the stars, and our own. star (the sun) in particular. These ought to be actually doing what we have foundsuch strong reason for believing that our earth did in the remote past, and the giant planets (still in the youth of their much longer lives) did, not so very long ago. They ought to be ejecting occasioral vast flights of meteoric masses frbm their interiors. Ourgun, no doubt— to take him as an example —would have to eject such masses with far groater energy than the earth must have employed during her sunlike youth, to send them beyond his own oontrol. For whereas, seven miles per second would have sufficed in the earth's case, 382 miles per secondi would have been required in the sun's. But then the sun is 327,000 times as massive"! and therefore as mighty, as the earth, ana no doubt volcanic ejections resulting from? that vast strength would, in adequate degree, surpass all that our earth could have done, even in the fullness of her youthful energy. We turn our telescopes,' then, on the' sun> to see whether he ever does such amazing expulsive work as this requires of him, perhaps hardly expecting ,to find signs of it. But lo ! he has been detected in the .very act. He has been caught ejecting flights of bodies from his interior with velocities so> great that not evea his mighty attractive power could ever bring them back again. In one such outburst velocities of 450 miles per second at his visible smface were indicated, which would be 68^ milesper second more than would be required totake such matter for ever away' from him.. Thia evidence would in reality suffice if it stood alone to account for all the ,<meteoric phenomena we have been dealing ..with, If he does this new, he must have done the like during all the millions of years of his past existence as recorded on the tablets of the earth's crust. If our sun does thia, somust his fellow suns, the stars, and theyalso during millions of past years. Billions of billions of billons of sun-expslled bodies, must therefore be travelling in multitudinous courses through interstellar space. And from this we can reason back to the very theory of planetary and terrestrial, ejection of meteors to which we had been already led, and from which we had reasoned on to solar ejections. Meteorites, meteor-streams, and comets would appear, then, to be products of expulsion from suns, from giant planets, and fronv orbs like ourearfch when in the sunlike state.. — •« Times," r " ' .

Among recent deaths in England waa that of Mr Watson, of Whjtby, aged 96, whose half-brother was a Bailor with Cap tain Cook, and witnessed the massacre of" the circumnavigator. , ' ' ' . Speaking of flies, a Burlington baseball player' says, "They come high 1 , - but we-< must have them. ■ ■ "