Returning homewards, through those profound abysses, to whose extremities we have adventured, and leisurely surveying the objects whose number and varieties struck us at first with an absorbing and most natural astonishment, we soon start the enquiry, What are these clusters doing?—What is their internal condition?—What their mechanisms?—And what the nature and affections of the bodies which compose them? It is manifest, that such investigations, in so far as we would rest them on observation, must be confined within our own cluster—the telescope, which has revealed the dim lustre of others, still failing to discriminate the peculiarities of their individual orbs; but if we analyze the system of which we form a part, and become familiar with the mode of its existence, a cautious use of the argument from analogy, will at least darkly illumine the obscurer objects which surround it.

I. In the first place, it is of importance to ascertain whether the stars are individually characterised by the same leading features, or—taking our Sun, which we know best, as a pattern object—whether and how far the distinct orbs of remote space may be accounted to resemble him? The old notion that these luminaries are of no significancy, except as ornaments to the earth, has lost hold, I believe, of all classes of minds, so that, assuming that the stars are also suns, shining like our luminary, of their own perennial virtue, we may step at once to consideration of the second or next higher point of probable resemblance,—are these myriads of suns encircled, like ours, by schemes of subservient planetary worlds?

The disclosures of the telescope are now before us5—the entire perspective of Modern Astromomy. Can we comprehend its wonders? Are its arrangements a fixed thing—a mere passing show—or are they results of a pre-existing state, and germinant of something future? These questions warn me, that again we break new ground, and enter on speculations, perhaps the most adventurous which have yet engaged the reason of Man.

Astronomy has recently been obliged to recognise a Matter—or rather a modification of Matter, wholly distinct from stars—a thin and filmy substance diffused through the stellar intervals, and spreading over regions so immense, that its magnitude or the space it fills, is absolutely inconceivable. It unquestionably becomes us not to admit an element so remarkable, and which, if real, must perform important functions, and materially affect our general views of things—until its claims have undergone the severest scrutiny ; and as I am desirous to convey to you full power of judging for yourself, I will here minutely follow the process of thought, by which Sir, William Herschel—only, however, at a comparatively late period in the course of his researches—was, slowly and almost reluctantly, led to the conviction of its reality.

In his earlier inquiries, Herschel was inclined to consider all the faintly illuminated spots in the heavens, as clusters so remote, that only their general illumination, and no individual object could be seen; and the inference, so far from being constrained, seemed to result from his whole previous experience.

Let us note the exact amount of evidence constituted by the speculations of the foregoing letter, on behalf of the Hypothesis that all existing stellar bodies sprung by virtue of the law of attraction, from the bosom of a chaos similar to the vague masses I have described. In so far as this Hypothesis undertakes to explain the nebulæ, I do not conceive that much of accessible knowledge is now wanting to confirm it; for, the agreement of the forms of the nebular substance with the natural results of the persevering action of gravity, seems almost demonstrated. But it must not be forgotten that there is another correlative and very extensive inquiry which this truth has not touched; The Hypothesis must alsoexplain the stars. If it is the true Cosmogony, and we have at length approached a right theory of the Formation of Things, we should indeed obtain from it a satisfactory idea of the meaning of that curious progression of structure, which so strikingly characterises the Nebulous masses; but it is no less imperative that it exhibit with proper distinctness, how the mass of stars around us, along with their peculiar features and arrangements, might have been evolved, in obedience to known mechanical laws, by the condensation of Nebulæ.

If our desire of knowledge did not quicken as its sphere expands, or if man, so long as an eminence is unsurmounted, could lay himself down in peace, satisfied with the view of the vastness and variety which already stretch out beneath him, doubtless our task had now ended, and the volume of Astronomy might have been closed. But Desire, happily insatiable, has no confine on this side the Infinite; and no sooner have we reached the elevation of one thought or idea which resolves some large portion of the unknown, than ambition is fired afresh, and speculation never at rest, takes wing towards remoter regions.

In the present instance indeed there is every encouragement to further venturous inquiry. The Nebular Hypothesis, in its relations to the planetary system, may be termed complete;—it comprehends its beginnings, establishes those elements on which its duration depends, and exhibits the causes and mode of its ultimate transition into a novel form; and thus—surveying it from its commencement to its close—we are as if in possession of that primeval Creative Thought which originated our system and planned and circumscribed its destiny. Now, in reference to one of these epochs, our Hypothesis seems to hold equal connexion with the whole contents of the Heavens,—the epoch, viz.

2. Guided by the Genius, whose prophetic eye pierced the obscurity, which, until then, had concealed the arrangements we have just unfolded—we advance cautiously, but without dread, to take cognizance of still higher schemes.—The arguments which induced Herschel to pronounce on the connexion and motion of the constituents of binary systems, penetrate much farther, and intimate as a general law, that every cluster or unusual aggregation of orbs must be systematic, and probably united by common motion. If it is unlikely that the principles of random scattering would produce numbers of double stars, it is plainly as unlikely that anytriple or quadruple bodies should be found in the whole sky ; and this holds even where the stars are more separated, as in the case of the six principal constituents of the Pleiades, against whose fortuitous aggregation within that space—as Michell long ago calculated—there is a balance of probabilities of 500,000 to 1. The presence of a great law thus lays it on astronomers as a command that they watch these higher systems, take their measurements with every minuteness, and transmit them to posterity. The results must be brilliant, and they are already foreshadowed. In a triple star in Cancer (ζ), we are certain of a common motion, in which three suns seem to revolve around a common central point; and in another—ψ CassiopeiÆ — one sun probably revolves around a second, while the two in union—a sun and an associated sun, circulate around the third.

We resume our progress. The fact has been already established of the existence of clusters or firmaments, distinct from ours, sustaining an independent position, as individual constituents of creation. Let us now go forth into infinity among these firmaments, and ascertain their character.

The number of such masses is very great. In the northern hemisphere, after making all allowances, those, whose places are fixed, cannot be fewer than between one and two thousand; and you will have a good idea how plentifully they are distributed, by remarking that this is at least equal to the whole number of stars which the naked eye perceives in any ordinary night. These clusters, the general aspects of which I am now to describe to you, have very various appearances to the telescope. In many of them, individual stars are distinctly defined. As they become more remote, the distances or intervals between the stars diminish, the light also growing fainter ; in their faintest stellar aspect, they may be compared to a handful of fine sparkling sand, or, as it is aptly termed, star-dust; and beyond this we see no stars, but only a streak or patch of milky light, like the unresolved portions of our own surrounding zone. This is the state in which they are more properly called Nebulæ, and in which there is risk of confounding them with a singular substance not partaking of the nature of stars, but very common in our firmament.

Madam,

I have been induced to make the brief series of letters addressed to you, thus public, because of a regret which, I believe, is widely felt, that the discoveries made in recent years, throwing most unexpected light upon the constitution—present and remote—of the Stellar Universe, should longer continue comparatively unknown, and concealed amid the varied and massive collections of our 'Learned Societies. Unfortunately, I am not at present in a condition to bestow on these discoveries a shadow of original interest, so that, in description, my pen can have only a borrowed liveliness; but as the illustrious men who share the glory of having achieved such acquisitions for mankind, have, not unequivocally, shown a disinclination to the humbler task of reducing them into a popular system, we have only the choice of consenting, that matter of unusual importance shall remain unfitted to fulfil the best purpose of truth—which is to instruct and elevate the general mind—or to permit the work to be attempted by some one with pretensions no higher than my own.

Previous to the commencement of this century the facts and speculations about to engage us were unknown in science. Before then, the planetary orbits seemed to encircle all accessible space ; they had eiFectively constituted bounds to systematic enquiry, for astronomers had never adventured into greater remotenesses, having, like the people, gazed at the farther heavens with vague and incurious eye—content to admire their beauty and confess their mystery.