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gests the necessity of receiving with caution, for the present, the generalisation that all the nebulous objects seen in the sky are remote star-firmaments. As, however, this forms the key of the essayist's position, so far as the nebulæ are concerned, it may be as well to let Sir John tell the result of his observations in his own words. The passage is extracted from the last edition of his "Outlines of Astronomy": "It must, therefore, be taken as a demonstrated fact that stars of the seventh or eighth magnitudes and irresolvable nebula may coexist within limits of distance not differing in proportion more than as nine to ten, a conclusion which must inspire some degree of caution in admitting as certain many of the consequences which have been rather strongly dwelt upon in the foregoing pages."
visible against the dark back-ground of the sky being the tracing of its course as it is thus brought up. The spiral nebulæ are not vortices of remote star-streams, bent into curves by orderly irregularities of movement; they are whiffs of infinitely thin curling smoke rolled up in a single twist. They are masses of luminous fog with very slight internal cohesion of parts, drifting through resistance, and, so dragged out into spiral lines:
"In the nebulæ we have loose matter of a thin and vaporous constitution, differing as more or less rare, more or less luminous, in a small degree; diffused over enormous spaces, in stragbrief curves, with no vestige of order or system, gling and irregular forms; moving in devious and or even of separation of different kinds of bodies. In the solar system we have the luminous separated from the non-luminous, the hot from the cold, the dense from the rare; and all luminous and non-luminous formed into globes, impressed with regular and orderly motions, which continue the same for innumerable revolutions and cycles. The spiral nebulæ, compared with the solar system, cannot be considered as other than a kind of chaos; and not even a chaos in the sense of a state preceding an orderly and stable system; for there is no indication in those objects of any tendency towards such a system. If we were to say that they appear mere shapeless masses, flung off perhaps, disturb those who are resolved to find in the work of creating solar systems, we might, every where worlds like ours, but it seems difficult to suggest any other reason for not saying so.
"So far, then, as the nebulæ are concerned, the improbability of their being inhabited appears to mount to the highest point that can be conceived. We may, by the indulgence of fancy, people the alis, with living beings of the same kind of substance as those bright appearances themselves; and in doing so we are not making any bolder assumption than we are when we stock the nebulæ with inhabitants, and call them in that sense distant worlds.'" (P. 232.)
summer clouds, or the beams of the aurora bore
The author of the Essay, however, does not find in these clouds inculcations of caution merely; they are in his eyes proof that all nebulæ are luminous fog. He holds them to be "lumps of light," in some cases resolvable by the telescope into sparkling dots. But these dots are not stars, they are merely brighter and denser parts of the curdled and granulated light. There are instances of like irresolvable luminosity furnished in the tails of comets. Such tails are manifestly vaporous masses through which stars are readily and distinctly seen. Nebula, therefore, are vaporous masses too; and this at once, in the essayist's eyes, accounts for the spiral arrangements of their parts, detected by Lord Rosse. Encke's comet is approaching the sun, because its rare filmy substance is moving through a medium that is capable of affording some resistance to its filminess. It may probably reach the sun after ten thousand revolutions round it, and its substance is probably one hundred thousand times denser than the re- Such are the conclusions of the essayist tarding medium through which it is re-in regard to these interesting objects that volving. But the spiral scrolls in many of the nebulæ only make one turn from their outer commencement to their inner termination. This is because their substance is only ten times denser than the retarding medium. Nebula are really the ten thousand times refined essence of comets' tails, and the exquisitely subtle substance of which they are composed, is whirling round, as the comet whirls about the sun, but it is so extremely light that the resisting ether through which it sweeps brings it up at one turn, the luminous spire
have excited so much attention, since the gigantic instrument of Lord Rosse has been added to the implements of astronomical research. It will be observed here that the gist of the matter is comprised in three distinct propositions. The nebula are not composed of stars: they are luminous vapor of a comet-like nature, and of extreme tenuity; and being only thin vapor, they are destitute of living inhab itants. The third of these propositions is made, in the reasonings of the essayist, to depend entirely upon the establishment
fore, are the premises that require to be examined. Touching the first, Professor Baden Powell writes thus, in his "Essay on the Unity of Worlds":
of the preceding two. Those two, there- | star-clusters should be arranged in a long column of space turned directly away from the earth, or, as the anonymous essayist puts the case:
"I am able to state on the authority of those who have actually seen the nebulæ in Lord Rosse's instrument, that the appearance is perfectly and brilliantly that of stars; distinct effulgent points of no sensible magnitude, and of whose stellar nature no doubt could remain on the mind of the observer." (P. 188.)
Here surely, then, the essayist is pleading a distinction without a difference. He speaks of the nebula as resolved into dots of light" by the telescope. But dots of light seen in the sky are stars. Nothing more is positively known of the fixed stars than that they are luminous points without discernible dimensions scattered in surrounding space. Whether such luminous points are contemplated by the unaided eye, or through the assistance of the telescope, can in no way concern their intrinsic natures. The sparkling dots" of the essayist are stars, and his "curdled lumps of light," in the majority of instances, are star-beds, if it is to be admitted that there are such things as stars in the sky.
But all the nebula have not been resolved into "star-dots,"-those, for instance, which are contained within the spaces of the Magellanic clouds, and to which Sir John Herschel alludes in the passage specified above, have not been so resolved. But it must be remembered that those nebula lie in a hemisphere of the heavens that never comes within the sky of the British Isles. The powerful instruments of Lord Lord Rosse have, therefore, never included them in their penetrating scrutiny. It will have been noticed that the sagacious astronomer who made them the subjects of especial attention with such instrumental aid as he had at his command during his sojourn at the Cape of Good Hope, did not feel himself warranted in drawing any definite conclusion from them, beyond the belief that they were near neighbors (speaking comparatively) of stars that he could distinctly discern. Other observers, who are competent to form their own opinions in the matter, do not seem to be satisfied fully upon this point. Sir John formed his belief avowedly upon what he deemed the extreme improbability that so many
"That the two nebulæ are thus approximately, spherical spaces is in the highest degree probable, not only from the peculiarity of their contents, which suggests the notion of a peculiar group of objects collected into a limited space, but from the barrenness as to such objects of the sky in the neigborhood of these Magellanic clouds. To suppose (the only other possible supposition) that they are two columns of space, with their ends turned towards us, and their lengths hundreds and thousands of times their breadths, would be too fanafter all, not explain the facts without further altotastical a proceeding to be tolerated; and would, gether arbitrary assumptions." (P. 212.)
It is hoped that the reader apprehends the point here to be that, in a space of the sky twelve or thirteen times wider than the full moon, numerous stars and numerous nebula are seen by tolerably large telescopes lying near together; that if the nebulæ are star-firmaments, they must be many times more remote than the stars (the essayist says a thousand times, but Captain Jacob says fifty), or the telescope would see them as stars too; and that there are so many of these nebulæ in this space, that it is very unlikely they would be distributed out further and further beyond each other, the only alternative to this arrangement being that they are not star-firmaments, but simply some kind of luminous substance of a dif ferent and less concrete nature than that of the stars amidst which they are grouped. Captain Jacob, astronomer to the Honorable East India Company, in his "Few More Words on the Plurality of Worlds," writes:
"The great Magellanic cloud is certainly not approximately spherical, for it does not present a nearly circular outline, it is of an irregular form approaching to quadrilateral.
"Sir John Herschel's catalogue of the smaller
Magellanic cloud shows but 39 nebula and clusters out of a total of 244 visible objects, and four of these are beyond the limits of the cloud; and not only are they so much more thinly scattered, but they also exhibit less variety, there being but five of the thirty-five marked as clusters. The remaining objects are stars from the seventh to the tenth magnitude inclusive, from which by must be derived; and to my mind there seems far the greatest part of the light of the cloud nothing so very extravagant or fantastical in supposing that the moderate number of thirty nebula and five clusters, have been casually arranged so
as to fall in the same line of vision with, but con- | unlikely than the existence of a flat ring siderably behind, the loose cluster of small stars round the globe of Saturn, or of a group composing the rest of the cloud." (Jacob, p. 7.) of thirty-five minute planetoid bodies within the precincts of the solar system. Under these circumstances, it is clear that the beam inclines very considerably from the side of the essayist to that of the plurality of firmamental star schemes. But there is yet another consideration, so weighty in itself, that we think it entirely sets the question at rest, and decides it against the essayist, although it does not seem to have occurred to any of the controversialists who have answered the author of the Essay.
In this reasoning we fully concur. There can be no doubt whatever that if the ring of Saturn had never been seen, and if the thirty-four planetoids had never been detected between Mars and Jupiter, the assumption, that either such a ring or such a group of miniature planets could exist in the universe, would have been deemed so improbable as to be rash and fantastic in the highest degree. Yet there the ring and planetoids are, and each instance stands alone, so far as observation allows us to The light of the filmy transparent comet judge, in the vast realms of space. There is so faint, that as the cometic luminosity really could be nothing more extraordi- travels away from the earth, it is lost to nary in such a distribution of remote star-sight long before its dimensions have been clusters, as the appearance of the Magel- dwindled down to an unappreciable mealanic clouds indicates, than there is in these sure. It disappears as a perceptible body, unquestionable instances of unique and ex- or goes out" from the failure of its light, ceptional arrangement. We think, there- and not from the loss of its size. Yet the fore, that the difficulty sagaciously sug- greatest distance at which the cometic gested by Sir John Herschel is fairly met; wanderers are ever seen, as Sir David and that Captain Jacob has shown, in the Brewster strikingly puts it, "falls short first place, that the essayist has conside- of the distance of the nearest fixed star by rably exaggerated the points upon which nine million of millions of miles." The he mainly rests his cause in this particular nearest nebulæ, on the other hand, at the phase of his arguments; and, in the second lowest estimate are considerably further place, that the improbability, if admitted off than the nearest fixed star, and at that in its strongest form, is far from being distance not only retain their brightness, conclusive in regard to the point the es- but even become more brilliant in proporsayist contends for. In our apprehension, tion as larger telescopes are directed tothe matter stands thus: on the one side wards them, instead of getting paler and there is Sir John Herschel, holding the more diffuse, às cometic luminosity does doctrine that nebulæ are remote firma- under the same circumstances. Is it conments in a general sense, but suggesting ceivable, then, that a filmy luminosity that caution upon the exceptional evidence of vanishes from faintness within the realms the Magellanic clouds. On the other side, of the planetary scheme, remains visible there are the facts that more and more nine million of millions of times further off, nebulæ, before deemed irresolvable, are when "ten thousand times more thin and constantly being resolved into distinct star- rare?" Earnestly, but with all due regroups, with every fresh increase of opti- spect for the opinions and authority of cal power brought to bear in the examin- the essayist, we submit that nothing but tion; that this exceptional instance, which "a conviction that has gradually grown "gives" Sir John Herschel "pause," has from various trains of speculation" could never been subjected to the scrutiny of the maintain such a theory. There is quite great cloud-resolver, Lord Rosse's magni- enough in this peculiarity of nebulous ficent instrument; that Lord Rosse's own light, apart from the fact of its resolvabilexperience, he having really the best prac-ity into stars, incontrovertibly to establish tical right of any living man to be admit- its entire distinctness from the nature of ted as an authority in the case, induces comets. Whatever it may be, this at least him to believe that, with sufficient optical is clear, it is not cometic luminosity ten power, all the nebulæ of the sky would thousand times refined. be converted into stars; and that if the exceptional instance of the Magellanic clouds were proved, it still allows the possibility of an alternative which is not more
VOL. XXXVII.-NO. I.
Having thus carefully and fairly weighed the geological and nebular evidence adduced by the essayist, and found it wanting, we proceed to listen to what he has
in them and in their contemporaries. Nor are
from those which give an interest, and thence
to urge in regard to the fixed stars. The
But again we submit that "succeeding
"That Copernicus, that Galileo, that Kepler,
should believe the stars to be suns in
unsettled condition of certain stars really
ter, and therefore most probably is nothing but water. Its oblate form is just such a figure as a huge drop of water would assume if in very rapid rotation. The belts of cloud, which sweep transversely across its broad face, prove that it has water about it in abundance. So that taking into account the "bottomless waters" of this planet, the great force with which its vast mass must gravitatingly draw down whatever is placed near its surface, and the small amount of solar influence which, at its remote distance, it receives, it becomes clear that any inhabitants that belong to it, must possess only the very lowest forms of organization and life. As there are no solid substances, like bone, in the planet, they must be devoid of skeletons. As the temperature is very depressed, they must be very sluggish and inactive in all their functions and operations. Jupiter comes out, therefore, a mere spherical mass of water, with a few cinders in the midst, and a damp drapery of cloud and mist drawn around it; and with, at the best, a population of boneless, pulpy, glutinous monsters rolling about in its watery recesses; or, it is an oblately spherical lump of ice, with a few shallow pools of water here and there upon its surface, and entirely devoid even of pulpy monstrous life.
We now at length come to that portion of the Essay which really most closely concerns the question at issue, although its author does not seem to have viewed it in this light,-namely, the consideration of the condition of the planets which are associated with the Earth in its subordination to the solar mass. Here the essayist finds warranty no less strong for rejecting entirely the existence of other worlds. Neptune has not light enough to be of any available use in the service of organization. Its sun-derived light and heat are 900 times less than the Earth's. Jupiter has a density not greater than it would
Saturn, with its liquid and vaporous rings, with its cork-like lightness, and its illumination ninety times less than the Earth's, is in the same category with Jupiter, except only that it is in every respect worse off; so that its pulpy monsters, in its icy waters, are too sluggish to be even "deemed alive." The asteroids contained in the spaces between Jupiter and Mars, are avowedly too small to be peopled with living things. But they are nevertheless highly important to the argument in one sense. There are thirty-four of them, and therefore at least the " majority of the planets are uninhabited." Mars, a comparatively near neigbor to the Earth, certainly does approach in a degree to its state of physical existence. It is of nearly the same size, and is composed of substance of analogous density. It has, too, its clouds and snow, and possibly it may have inhabitants to boot. But it has longer years and a colder climate than the Earth. It has, too, really a smaller mass, and "perhaps no atmospheric investment;" therefore, after all, its inhabitants can only
have if it were entirely composed of wa-be of the rudimentary nature of corallines