FIFTH WEEK-FRIDAY.

XI. THE STARRY HEAVENS.-NEBULE.

SIR WILLIAM HERSCHEL, by the use of his powerful telescopes, has made other most interesting discoveries in the starry heavens, some of which it will be the object of this paper briefly to detail, as throwing light on the condition of the universe, and demonstrating that the same mighty hand, which "wheels the rolling spheres" in our own system, is equally employing its amazing powers in the most distant regions, and regulating the material world every where, so far as we are able to discern, by the same laws, under some remarkable varieties of application.

We have already noticed the wonderful discovery of the apparently general arrangement, whereby the innumerable suns, of which the universe is composed, are thrown into groups, each containing vast numbers of these splendid bodies, and comprehending systems of their own. Of these nebulæ, as they are called, our own seems to be of a singular figure, forming a stratum of which the thickness is small in comparison with its length and breadth, and which is divided into two branches, inclined at a small angle to each other, near the point in which our sun, with its planetary system, is situated. This figure seems, at least, to account for the appearances of the heavens, with their milky way, studded with innumerable stars, which branch off in one place in a remarkable manner from the main body, and which, as we have observed, decrease rapidly in numbers, in proportion to their distance from that singular belt. The other nebulæ are of various forms, and even seem to differ from each other in their nature. Sir William Herschel divides them into six classes, of which the two first appear to be distinguished merely by their relative distance from us, but the rest to be in a state altogether

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different from any thing of which we have experience. These latter, he describes under the four heads of nebulæ, in which there is no appearance whatever of stars, planetary nebulæ, stellar nebulæ, and nebulous stars. Of these the variety is very great, some being formed of little flaky masses, like "wisps of cloud," adhering to small stars; others being of a round or oval form, increasing more or less in density and brightness towards the central point; others offering "the singularly beautiful and striking phenomenon, of a sharp and brilliant star, surrounded by a perfectly circular disc or atmosphere ;" others, again, of more rare occurrence, are annular, exhibiting, in the central opening, a faint hazy light; and, last of all, come nebulæ, which have " exactly the appearance of planets,-round, or slightly oval discs, in some instances quite sharply terminated, in others a little hazy at the borders, and of a light exactly equable, or only a very little mottled, which, in some of them, approaches in vividness to that of actual planets." These last are bodies of enormous magnitude,- -so large, indeed, that they would include the whole of our planetary system within their diameter, forming masses of solid matter, if they are solid, such as the greatest stretch of imagination cannot grasp.

"The nebulæ," says the younger Herschel, "furnish, in every point of view, an inexhaustible field of speculation and conjecture. That by far the larger share of them consists of stars, there can be little doubt; and in the interminable range of system upon system, and firmament upon firmament, which we thus catch a glimpse of, the imagination is bewildered and lost. On the other hand, if it be true, as, to say the least, seems extremely probable, that a phosphorescent, or self-luminous matter also exists, disseminated through extensive regions of space, in the manner of a cloud or fog,-now assuming capricious shapes, like actual clouds, drifted by the wind, and now concentrating itself, like a cometic atmosphere, around particular stars;-what, we naturally.

ask, is the nature and destination of this nebulous matter? Is it absorbed by the stars, in whose neighbourhood it is found, to furnish, by its condensation, their supply of light and heat? Or is it progressively concentrating itself, by the effort of its own gravity, into masses, and so laying the foundation of new sidereal systems, or of insulated stars?"*

The author naively remarks, that it is easier to propound such questions, than to offer any probable reply to them; and it would be well if other astronomers were to imitate the modesty and philosophical forbearance of this eminent man. But there are, unfortunately, philosophers, who feel pleasure in every conjecture by which an intelligent First Cause may be excluded from the universe; and the obscure and doubtful phenomena afforded by these nebulous appearances, have furnished one of the most profound mathematicians of his classt with a theory, by which he attempts to show, that the whole construction of nature depends on mere unintelligent mechanical powers. He supposes, for example, that our own sun, with his planetary system, was originally nothing else than a part of a universally diffused phosphorescent vapour, which, condensing into a nucleus, gave rise to a revolving sun, of excessive heat; that as the heat diminished, the solar atmosphere contracted, leaving portions of itself detached by the centrifugal motion, which became gradually condensed into solid planets and satellites; and these he, with much ingenuity, attempts to show, from mechanical considerations, would assume the form and motions which we find actually impressed on them. Mr Whewell mentions this "nebular hypothesis," as he calls it, and triumphantly shows, that even granting it could account for the phenomena, it could not be held, in the most remote degree, to prove the sufficiency of mechanical causes without intelligence and design. On this highly satisfactory reasoning I cannot enter, but must refer the reader to the work itself; and Herschel's Astronomy. † Laplace.

I am quite sure that no candid mind can resist the conclusion to which he comes, that, whatever may be the seientific merits of this hypothesis, they cannot, in sound reason, affect at all the view of the universe as the work of a wise and great Creator. "Let it be supposed," observes he in conclusion, “that the point to which this hypothesis leads us, is the ultimate point of physical science; that the farthest glimpse we can obtain of the material universe by our natural faculties, shows it to be occupied by a boundless abyss of luminous matter; still, we ask, how space came to be thus occupied, how matter came to be thus luminous? If we establish, by physical proofs, that the first fact which can be traced in the history of the world is, that "there was light,' we shall still be led, even by our natural reason, to suppose that, before this could occur, God said, let there be light.""

Dr Nichol, who adopts the hypothesis of Laplace, as to the gradual conversion of nebulæ into stellar and planetary systems, and illustrates it in a very striking manner, deduces from it the following pleasing and sublime views: The ideas I have presented to you-august and strange though they are should not appear in contradistinction to what every moment is passing around us. Supposing these phenomena did unfold the long growth of worlds, where is the intrinsic difference between that growth and the progress of the humblest leaf, from its seed to its intricate and most beautiful organization? The thought that one grand and single law of attraction, operating upon diffused matter, may have produced all those stars which gild the heavens, and, in fact, that the spangling material universe is, as we see it, nothing other than one phase of a mighty progress, is indeed truly surprising; but I appeal to you again, in what essential it were different from the growth of the evanescent plant? There, too, rude matter puts on new forms, in outward shape most beauteous, and in mechanism most admirable: and there cannot be a more asto

nishing process, or a mightier power, even in the growth of a world! The thing which bewilders us, is not any intrinsic difficulty or disparity, but a consideration springing from our own fleeting condition. We are not rendered incredulous by the nature, but overwhelmed by the magnitude, of the works;- -our minds will not stretch out to embrace the periods of this stupendous change. But time, as we conceive it, has nothing to do with the question, we are speaking of the operations, and tracing the footsteps, of one who is above all time,—we are speaking of the energies of that Almighty Mind, with regard to whose infinite capacity a day is as a thousand years, and the lifetime of the entire human race but as the moment which dies with the tick of the clock which marks it—which is heard and passes."*

FIFTH WEEK-SATURDAY.

XII. THE STARRY HEAVENS.-BINARY STARS.

THERE is yet another singular phenomenon in the starry heavens, which shall form the subject of this day's paper, I allude to the curious fact of the existence of binary revolving stars. These are very numerous. Sir William Herschel has enumerated upwards of 500, and Professor Strave, of Dorpat, has recently added to this number between 2000 and 3000. When these combinations were first observed, it was thought probable, that their extreme apparent proximity would enable astronomers to ascertain their distance from the earth, by the discovery of an annual parallax; for supposing, as might naturally be expected, that one of the combined stars should be nearer the earth than the other, and that both should prove to be stationary in relation to each other, the motion of the earth in her orbit would cause these stars to alter their apparent position; and, if that should

* Architecture of the Heavens, pp. 143, 144. f He