it has stood a moderate trial; it has stood all the trial that offered, which is always something; but you are still obliged to feel that, when the ultimate test is applied, smash may go the whole concern. Lord Rosse applied an ultimate test; and smash went the whole concern. Really I must have laughed, though all the world had been angry, when the shrieks and yells of expiring systems began to reverberate all the way from the belt of Orion; and positively at the very first broadside delivered from this huge four- decker of a telescope.
But what was it then that went to wreck? That is a thing more easy to ask than to answer. At least, for my own part, I complain that some vagueness hangs over all the accounts of the nebular hypothesis. However, in this place a brief sketch will suffice.
Herschel the elder, having greatly improved the telescope, began to observe with special attention a class of remarkable phenomena in the starry world hitherto unstudied, viz.: milky spots in various stages of diffusion. The nature of these appearances soon cleared itself up thus far, that generally they were found to be starry worlds, separated from ours by inconceivable distances, and in that way concealing at first their real nature. The whitish gleam was the mask conferred by the enormity of their remotion. This being so, it might have been supposed that, as was the faintness of these cloudy spots or nebulæ, such was the distance. But that did not follow: for in the treasury of nature it turned out that there were other resources for modifying the powers of distance, for muffling and unmuffling the voice of stars. Suppose a world at the distance x, which distance is so great as to make the manifestation of that world weak, milky, nebular. Now let the secret power that wields these awful orbs, push this world back to a double distance! that should naturally make it paler and more dilute than ever: and yet by compression, by deeper centralization, this effect shall be defeated; by forcing into far closer neighborhood the stars which compose this world, again it shall gleam out brighter when at 2_x_ than when at x. At this point of compression, let the great moulding power a second time push it back; and a second time it will grow faint. But once more let this world be tortured into closer compression, again let the screw be put upon it, and once again it shall shake off the oppression of distance as the dew-drops are shaken from a lion's mane. And thus in fact the mysterious architect plays at hide-and-seek with his worlds. 'I will hide it,' he says, 'and it shall be found again by man; I will withdraw it into distances that shall seem fabulous, and again it shall apparel itself in glorious light; a third time I will plunge it into aboriginal darkness, and upon the vision of man a third time it shall rise with a new epiphany.'
But, says the objector, there is no such world; there is no world that has thus been driven back, and depressed from one deep to a lower deep. Granted: but the same effect, an illustration of the same law, is produced equally, whether you take four worlds, all of the same magnitude, and plunge them simultaneously into four different abysses, sinking by graduated distances one below another, or take one world and plunge it to the same distances successively. So in Geology, when men talk of substances in different stages, or of transitional states, they do not mean that they have watched the same individual stratum or phenomenon, exhibiting states removed from each other by depths of many thousand years; how could they? but they have seen one stage in the case A, another stage in the case B. They take, for instance, three objects, the same (to use the technical language of logic) generically, though numerically different, under separate circumstances, or in different stages of advance. They are one object for logic, they are three for human convenience. So again it might seem impossible to give the history of a rose tree from infancy to age: how could the same rose tree, at the same time, be young and old? Yet by taking the different developments of its flowers, even as they hang on the same tree, from the earliest bud to the full- blown rose, you may in effect pursue this vegetable growth through all its stages: you have before you the bony blushing little rose-bud, and the respectable 'mediæval' full-blown rose.
This point settled, let it now be remarked, that Herschel's resources enabled him to unmask many of these nebulæ: stars they were, and stars he forced them to own themselves. Why should any decent world wear an alias? There was nothing, you know, to be ashamed of in being an honest cluster of stars. Indeed, they seemed to be sensible of this themselves, and they now yielded to the force of Herschel's arguments so far as to show themselves in the new character of nebulæ spangled with stars; these are the stellar nebulæ; quite as much as you could expect in so short a time: Rome was not built in a day: and one must have some respect to stellar feelings. It was noticed, however, that where a bright haze, and not a weak milk- and-water haze, had revealed itself to the telescope, this, arising from a case of compression, (as previously explained,) required very little increase of telescopic power to force him into a fuller confession. He made a clean breast of it. But at length came a dreadful anomaly. A 'nebula' in the constellation Andromeda turned restive: another in Orion, I grieve to say it, still more so. I confine myself to the latter. A very low power sufficed to bring him to a slight confession, which in fact amounted to nothing; the very highest would not persuade him to show a star. 'Just one,' said some coaxing person; 'we'll be satisfied with only one.' But no: he would not. He was hardened, 'he wouldn't split.' And Herschel was thus led, after waiting as long as flesh and blood could wait, to infer two classes of nebulæ; one that were stars; and another that were not stars, nor ever were meant to be stars. Yet that was premature: he found at last, that, though not raised to the peerage of stars, finally they would be so: they were the matter of stars; and by gradual condensation would become suns, whose atmosphere, by a similar process of condensing, would become planets, capable of brilliant literati and philosophers, in several volumes octavo. So stood the case for a long time; it was settled to the satisfaction of Europe that there were two classes of nebulæ, one that were worlds, one that were not, but only the pabulum of future worlds. Silence arose. A voice was heard, 'Let there be Lord Rosse!' and immediately his telescope walked into Orion; destroyed the supposed matter of stars; but, in return, created immeasurable worlds.
As a hint for apprehending the delicacy and difficulty of the process in sidereal astronomy, let the inexperienced reader figure to himself these separate cases of perplexity: 1st, A perplexity where the dilemma arises from the collision between magnitude and distance:—is the size less, or the distance greater? 2dly, Where the dilemma arises between motions, a motion in ourselves doubtfully confounded with a motion in some external body; or, 3dly, Where it arises between possible positions of an object: is it a real proximity that we see between two stars, or simply an apparent proximity from lying in the same visual line, though in far other depths of space? As regards the first dilemma, we may suppose two laws, A and B, absolutely in contradiction, laid down at starting: A, that all fixed stars are precisely at the same distance; in this case every difference in the apparent magnitude will indicate a corresponding difference in the real magnitude, and will measure that difference. B, that all the fixed stars are precisely of the same magnitude; in which case, every variety in the size will indicate a corresponding difference in the distance, and will measure that difference. Nor could we imagine any exception to these inferences from A or from B, whichever of the two were assumed, unless through optical laws that might not equally affect objects under different circumstances; I mean, for instance, that might suffer a disturbance as applied under hypoth. B, to different depths in space, or under hypoth. A, to different arrangements of structure in the star. But thirdly, it is certain, that neither A nor B is the abiding law: and next it becomes an object by science and by instruments to distinguish more readily and more certainly between the cases where the distance has degraded the size, and the cases where the size being really less, has caused an exaggeration of the distance: or again, where the size being really less, yet co-operating with a distance really greater, may degrade the estimate, (though travelling in a right direction,) below the truth; or again where the size being really less, yet counteracted by a distance also less, may equally disturb the truth of human measurements, and so on.
A second large order of equivocating appearances will arise,—not as to magnitude, but as to motion. If it could be a safe assumption, that the system to which our planet is attached were absolutely fixed and motionless, except as regards its own internal relations of movement, then every change outside of us, every motion that the registers of astronomy had established, would be objective and not subjective. It would be safe to pronounce at