« ՆախորդըՇարունակել »
of arrangement and proportions of their parts from any compound bodies hitherto known to us; and are of deep interest, therefore, as representing an aggregation, distinct from that of the earth, of the same elements diffused beyond its sphere. Almost might we venture to call them specimens of planetary matter, since that which exists in the space intermediate between the earth and other planets may have the same relation to both. And if indulging in such speculation, we might go yet further, and find argument in these facts for that great theory of modern astronomy, which regards all the planets as formed by the successive condensation of rings of nebulous matter, concentric with the Sun-the matter being the same, but variously aggregated, from physical causes varying during the condensation of each planet.
Our readers will thank us for quoting an eloquent passage from Humboldt in relation to this subject. After alluding to the several media, light, radiant heat, and gravitation, through which we hold relation to the world of nature without, he adds :—
'But if in shooting stars and meteoric stones we recognize planetary asteroids, we are enabled by their fall to enter into a wholly different and more properly material relationship with cosmical objects. Here we no longer consider bodies acting upon exclusively from a distance, but we have actually present the meteorical particles themselves, which have come to us from the regions of space, have descended through our atmosphere, and remain upon the earth. A meteoric stone affords us the only possible contact with a substance foreign to our planet. Accustomed to know non-telluric bodies solely by measurement, calculation, and the inferences of our reason, it is with a kind of astonishment that we touch, weigh, and analyse a substance belonging to the world without. The imagination is stimulated, and the intellect aroused and animated, by a spectacle in which the uncultivated hind sees only a train of fading specks in the clear sky, and apprehends in the black stone which falls from the thundering cloud only the rude product of some wild force of nature.'
Though no new element has yet been discovered in meteoric stones, we must not carry this negative beyond present proof. Analyses of other specimens may afford other results; and we are not yet warranted in omitting any opportunity of further research. Besides the chance of new ingredients, such examination enables us to classify with more certainty these products of other regions of space, and thereby better to interpret the mystery of their origin and movements.
Another speculation still occurs in connexion with aerolites. The researches of the last fifty years have disclosed to us some twenty new substances, hitherto undecomposed, and most of them metallic in kind. Certain of these substances exist only in single specimens-others are rare in occurrence and small in quantity. It has puzzled naturalists to conceive the purpose
which matters thus rare and insulated can fulfil in the economy of our globe. It is hardly probable, though possible, that these minute superficial specimens represent larger quantities in the interior of the earth. But is it not conceivable, looking to the composition of aerolites, that some of their elements, thus rare with us, may enter more abundantly into the composition of other planetary bodies? In the varying conditions of magnitude, figure, and specific gravity, as well as in the especial peculiarities of rings, belts, satellites, &c., we have the certain proof of different modes of aggregation in each case. May we not reasonably suppose that this difference has extended to the kind and proportion of the elements thus segregated and condensed from the vast material for which we vainly seek a befitting name? Speculations such as these do not fairly enter within the domain of science, but they border upon it, and now and then become the paths leading to new and unexpected truths. The objects of research are seemingly, indeed, too remote for access; but we have just seen how strangely some of them are actually brought within our reach. And when a single small instrument, like the polariscope, suffices to tell us the condition of light, whether issuing or reflected from a body a hundred million of miles distant in space-or when the perturbations of certain known planets are made by the astronomer to indicate the place and motions of one yet wholly unknown-it becomes difficult to despair of anything which time and genius may yet effect in the discovery of truth.
So far on the subject of aerolites, more especially; of which we have spoken thus fully, regarding this class of meteoric phenomena as best interpreting the others treated of in the works before us. It will have been seen already how closely all are allied, as well in various points of outward aspect, as in regard to the questions which concern their real nature and origin. One effect of this has been to render somewhat obscure to the untutored reader much of what even the ablest men have written on the subject. In the work of MM. Gravier and Saigey, for instance, the history of Meteorites, though divided into periods, is perplexed by the continual passage from one class to another, and from observation to theory. We have at least endeavoured to avoid this perplexity as far as seemed to ourselves possible in our actual ignorance of many of the relations of the phenomena. In proceeding now to those of the meteoric globes or fire-balls, and the shooting-stars, we are following a provisional arrangement, which may hereafter be cancelled; and are adopting names as we find them, since no better nomenclature has yet been brought to this part of science.
The same thing has happened in other sciences; and such steps are natural in the history of all human progress.
The luminous globes are those in closest connexion with aerolites :--inasmuch as we have various well-attested instances of stones-single or numerous-falling at the time of such appearances, and in sequel to explosions which would seem to rend asunder some larger volumes of matter. The following description of the ordinary character of the Bolide we take chiefly from our French authors, who correct some exaggerations of Chladni on this subject. They have claim to be considered an authority, since one of them, by incessant observation for several years, witnessed as many of these great meteors as the actual number noted during the same period by all other observers in every part of the globe.
These meteors appear to move in the arcs of great circles. They do not come equally from all points of the horizon, but affect certain principal directions. No movement of rotation is recognized in them. Their apparent disk is greatly enlarged by irradiation; and is occasionally seen to exceed the circumference of the full moon-which, at the distance of 110 miles, would give a diameter of about a mile. Their form is always circular. The amount of their illumination is much less than that of the moon. Their height is various, but often far beyond the limits of our atmosphere. They appear and disappear suddenly, without sensible change of diameter; sometimes bursting, but without noise; and often leaving a train of light behind. Their duration seldom exceeds a few seconds. Their velocity approximates to that of the earth, or other planets.
One curious fact relating to these meteors, and still more to shooting-stars, is, that they appear now and then to ascend, or to alternate in ascent or descent, as if new and opposite forces were suddenly brought into action. Chladni and others have sought explanation of this, either in resistance of the air compressed by rapid descent, or in the effects of explosion or ignition in the masses themselves. More recently, however, doubt has been thrown on the reality of these appearances, and the authority of Bessel as to their improbability is one that must have much weight on the subject. Still it is a point open to future observation and inquiry.
As is the case in every other part of science, the record of facts regarding these igneous meteors has become of late years infinitely more copious and exact. We have already noticed the extraordinary Chinese register, brought down from a very remote date. No other country, nor any age before the present, furnishes a like document. The first formal catalogue of remarkable meteors,
VOL. XCII. NO, CLXXXIII.
teors, of all classes, is that of a very eminent observer, M. Quetelet, published in 1837; and again, with large additions, in 1841. There soon followed the catalogue of Mr. Herrick, in America, and that of M. Chasles, presented to the Académie des Sciences in 1841-containing much curious retrospective information, and particularly as to the recorded falls of shooting-stars. The latest catalogue is that by Professor Baden Powell-presented in series at the five last meetings of the British Association, and published in their Annual Reports. Professing to be merely a continuation of Quetelet's Catalogue, and to form a nucleus for future collection, it is, in truth, a most copious and valuable register of these phenomena, attesting-if any attestation were necessary-the equal zeal and ability of its author. We will not call it complete, because no record of these vagrant and fugitive appearances can be so. We do not, for instance, find noted in the Report for 1851 a very remarkable meteor, of which we ourselves witnessed the appearance and disruption on the 30th September, 1850, from the Observatory at Cambridge, in Massachussets; and which has been fully described by Mr. Bond, the distinguished astronomer of that university. But many of these lacuna will be filled up; and meanwhile the catalogue is ample enough to furnish an admirable basis for future observation and theory.
We have noted the frequent connexion of these igneous meteors with falling stones; and this is, in truth, the question of greatest interest regarding them. Are they always associated with some form of matter analogous to that of known aerolites, but which escapes detection, either by falling out of human sight, or by the passage forwards of the meteor in its orbit, without precipitation of its contents? Taking the question generally, we incline to answer at once in the affirmative. It must be admitted that stones have sometimes fallen from what seems to be a clear heaven; or with no other appearance than that of a small circular cloud suddenly forming in the sky. But these, as far as we know, are events of the daytime; and what is seen as a dark form under the light of the sun may appear a fiery globe in the darkness of night. If it be well proved in a few cases that these fire-balls exploding have thrown down stones upon the earth, the
*The most striking circumstances in this meteor were, the long time (more than an hour) the nebulous light was visible after the explosion-the great distinctness of the nucleus, an elongated luminous space being projected, as it were, ahead of it-the perfectly cometary figure and aspect of the meteor a quarter of an hour after its first appearance, a fact strongly adverted to by Mr. Bond-and the rotary motion of the luminous elongation-amounting to nearly 90° within twenty minutes, and producing a sort of whorl, resembling some of the nebulæ so beautifully depictured from Lord
Rosse's late observations.
presumption becomes strong that analogous meteorical elements are present in all, whether precipitated or not. M. Saigey does not fully admit the relation of bolides and aerolites; but we believe the argument fairly to stand as we have stated it.
The subject of Shooting Stars (étoiles filantes) separates itself somewhat further from the phenomena already described, though still manifestly connected in various ways. The more important peculiarities here are the smaller size of these meteors; their infinitely greater frequency; the arcs they describe; their frequent occurrence in showers; and the observed periodicity in certain of these latter occurrences. The difference of magnitude is the least important of their characters; since we find every gradation of size, from the shooting scintilla of light to globes large as the moon. Those gradations, partially visible to any eye gazing into the depths of the sky on a clear night, are especially seen during the showers of stars just adverted to. The periodicity of some of these showers is the point of greatest interest in the inquiry ; a research still very imperfect, but which time is certain to complete, and probably at no distant period.
The common aspect of shooting stars needs no description. It was one of the earliest objects of science, as directed to them, to determine their heights, duration, and velocity; and on these points we owe much to the persevering labours of Brandes and Benzenburg; an ample narrative of whose observations is given in the French work before us. Begun as early as 1798, they were continued at intervals of time, and in different places, for a period of thirty-five years; Brandes dying in 1834, just after he had received the account of that prodigious fall of shooting stars in America, on the 12th and 13th November, which gave at once larger scope and better definition to all our views of these phenomena. To determine the points just mentioned, it was essential to have two observers at least, and a base of sufficient length for separate observation, Equally essential was it to assure the identity of the objects seen; for which recourse was had to the exact time of appearance, as well as to the apparent brilliancy, swiftness, and length of train of each star observed. Observation strictly simultaneous was needful to success; and this could only be got by knowing the precise difference of longitude between the stations. The base first taken, two leagues in length, proved too short to furnish the parallax required. In 1801 the inquiry was resumed, with the aid of two fresh observers; and four points were taken, the extremes of which, Hamburgh and Elberfeld, were about 200 miles distant. Here again it may be presumed that the separation was too great, since, out of a great number observed, only five shooting stars could be actually iden