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that this wonder, whatever it may be in itself, has been there from all times; but I never took notice of anything like it among the rest of the fixed stars."

Fig. 72 exhibits a view of this phenomenon as seen by Dr. Long in 1741 with a seventeen-feet refracting telescope, which appears exactly of the same shape as originally delineated by Huygens; but the apparent magnitudes of the stars connected with it are more accurately shown than in the engraved delineation of Huygens. Dr. Long says that the luminous space has sometimes appeared to him nearly of the same shape as the figure which is formed by the seven stars within it. Fig. 73 represents the same nebula, as seen by Sir W. Herschel in the year 1774 and in 1811. Its shape appears considerably different from the delineations of Huygens and Dr. Long; but the stars within and around it, which are common to both delineations, appear nearly in the same relative positions. Sir John Herschel has given a representation of this nebula, as viewed through the twenty-feet reflector at Slough, which appears considerably different from the figures to which I have referred. I have frequently viewed this phenomenon with telescopes of different sizes, particularly with a six feet and a half achromatic, having an aperture of four inches diameter, and which showed sidereal objects with great brilliancy and distinctness; but the shape of the object appeared more nearly resembling Dr. Long's representation (fig. 72) than any other delineation I have seen. A fourth star was distinctly seen in addition to the three represented by Dr. Long near the head of the opening, but smaller than the other three, and forming with them a small irregular square. The three other stars, instead of being within the one side of the nebula, as represented in both the figures, appeared quite beyond it, but nearly in a line with its margin. Whether this was owing to the inaccuracy of the delineation or to the actual change of the nebula I do not pretend to determine. The left-hand branch of the nebula likewise appeared considerably longer than here represented; but I cannot pretend to say what the appearance may be as seen through a twenty-feet reflecting telescope.

In forming a proper conception of this object, it is of some importance to ascertain the exact appearance it has presented at different periods, and whether there be reason to conclude that it has been subject to changes. The following is Sir J. Herschel's description of this phenomenon:

"I know not how to describe it better than by comparing it with a curdling liquid, or a surface strewed over with flocks of wool, or to the breaking up of a mackerel sky, when the clouds of which it consists begin to assume a cirrhous appearance. It is not very unlike the mottling of the sun's disk, only, if I may so express myself, the grain is much coarser and the intervals darker, and the flocculi, instead of being generally round, are drawn into little wisps. They present, however, an appearance of being composed of stars, and their aspect is altogether different from that of resolvable nebulæ. In the latter we fancy by glimpses that we see stars, or that, could we strain our sight a little more, we would see them; but the former suggests no idea of stars, but rather of something quite distinct from them."

The following are some of Sir W. Herschel's remarks on this nebula, and on the stars with which it is connected:

"In the year 1774, the 4th of March, I observed the nebulous star which is the 43d of the Connoissance des Temps, and is not many minutes north of the great nebulæ : but at the same time I also took notice of two similar, but much smaller, nebulous stars, one on each side of the large one, and at nearly equal distances from it. (See fig. 73, &c.) In 1783 I examined the nebulous star, and found it to be faintly surrounded with a circular glory of whitish nebulosity, faintly joining it to the great nebula. About the latter end of that year I remarked that it was not equally surrounded, but most nebulous towards the south. In 1784 I began to entertain an opinion that the star was not connected with the nebulosity of the great nebulæ of Orion, but was one of those which are scattered over that part of the heavens. In 1801, 1806, and 1810, this opinion was fully confirmed by the gradual change which happened in that great nebula to which the nebulosity surrounding the star belongs; for the intensity of light about the nebulous star had by this time been considerably reduced by the attenuation or dissipation of the nebulous matter, and it seemed now to be pretty evident that the star is far behind the nebulous matter, and that, consequently, its light in passing through it is scattered and deflected so as to produce the appearance of a nebulous star.” "When I viewed this interesting object in December, 1810, I directed my attention particularly to the two nebulous stars by the sides of the large one, and found they were perfectly free from every

nebulous appearance, which confirmed not only my former surmise of the great attenuation of the nebulosity, but also proved that their former nebulous appearance had been entirely the effect of the passage of their feeble light through the nebulous matter spread out before them. The 19th of January, 1811, I had another critical examination of the same object, in a very clear view, through the forty-feet telescope; but, notwithstanding the superior light of this instrument, I could not perceive any remains of nebulosity about the two small stars, which were perfectly clear, and in the same situation where, about thirty-seven years before, I had seen them involved in nebulosity. If, then, the light of these three stars is thus proved to have undergone a visible modification in its passage through the nebulous matter, it follows that its situation among the stars is less distant from us than the largest of the three, which I suppose to be of the eighth or ninth magnitude. The farthest distance, therefore, at which we can place the faintest part of the great nebula in Orion, to which the nebulosity surrounding the star belongs, cannot well exceed the region of the stars of the seventh or eighth magnitude."

From these observations it would appear that the nebulosities connected with the great nebula are subject to certain changes, and that its distance from our system is less than that of stars of the eighth magnitude, since a portion of the neb ulous matter interposes between our sight and stars of this description. But this distance must be very great. If stars of the eighth magnitude are to be considered at an average as eight times farther distant than those of the first, then this nebula cannot be supposed to be less than 320,000,000,000,000, or three hundred and twenty billions of miles from the earth. If its diameter at this distance subtend an angle of ten minutes, which it nearly does, its magnitude must be utterly inconceivable. It has been calculated that it must exceed 2,000,000,000,000,000,000, or two trillions of times the dimensions of the sun, vast and incomprehensible as these dimensions are.

This nebula has never yet been resolved into stars by the highest powers of the telescope that have yet been applied; nor is there any reason to believe that it consists of a system of stars, as is the case with many other nebula which appear much smaller, and are evidently more distant. It is therefore,

in all probability, a mass of self-luminous matter not yet formed into any system or systems, but of what nature it would be vain to conjecture. Whether it is more condensed than when it was first observed nearly two hundred years ago, as some have conjectured, or whether any portions of it have shifted their position, as seems to have been the opinion of Sir W. Herschel from the observations above stated, appears, on the whole, somewhat uncertain. On this point Sir J. Herschel makes the following remarks: "Several astronomers, on comparing this nebula with the figures of it handed down to us by its discoverer, Huygens, have concluded that its form has undergone a perceptible change; but when it is considered how difficult it is to represent such an object duly, and how entirely its appearance will differ even in the same telescope, according to the clearness of the air or other temporary causes, we should readily admit that we have no evidence of change that can be relied on."

The phenomenon we have now been contemplating is calculated to suggest a train of reflections and inquiries: What is the grand design in the system of nature of such an immense mass of luminosity-a mass of luminous matter to which the whole solar system is but only as a point-a mass. at least twenty-nine millions of times larger than a globe which would fill the orbit of Uranus ?* Is it in a state of perfection completely answering the ultimate end of its creation, and will it remain for ever in that state? Or is it only a chaotic mass of materials progressing towards some glorious consummation in the future ages of eternity, when worlds and systems will be evolved from the changes and revolutions now going forward within its boundaries? Or may we suppose that a luminosity of so vast extent serves the purpose of a thousand suns to ten thousand of opaque globes which revolve within its wide circumference? Considering the diversified methods of Divine operation, and the vast variety of modes by which worlds are arranged and enlightened, it is not impossible, nor even improbable, that numerous worlds may be in this way illuminated with a perpetual and uninterrupted day. As there appear to be worlds connected with one sun, with two, with three, and even more suns, so there may be thousands of worlds cheered and illuminated without such a sun as

* See page 196.

ours, and with an effulgence of light which is common to them all. But on these points we shall never be able to arrive at certainty so long as we sojourn in this sublunary sphere. Suffice it to say, that such an enormous mass of luminous matter was not created in vain, but serves a purpose in the Divine arrangements corresponding to its magnitude and the nature of its luminosity, and to the wisdom and intelligence of Him whose power brought it into existence. It doubtless subserves some important purpose, even at the present moment, to worlds and beings within the range of its influence. Were we placed as near it as one half the distance of the nearest star, great as that distance is, from such a point it would exhibit an effulgence approximating to that of the sun; and to beings at much nearer distances it would fill a large portion of the sky, and appear with a splendour inexpressible. But the ultimate design of such an object, in all its bearings and relations, may perhaps remain to be evolved during the future ages of an interminable existence; and, like many other objects in the distant spaces of creation, it excites in the mind a longing desire to behold the splendid and mysterious scenes of the universe a little more unfolded.

SECTION V.-On the Nebular Hypothesis.

I have already stated that the nebulæ may be arranged into two classes, the resolvable and the irresolvable. When Sir W. Herschel commenced his observations on the nebulous part of the heavens, and for several years afterward, he was disposed to consider the nebula in general to be no other than clusters of stars disguised by their very great distance; but a long experience and better acquaintance with the nature of nebulæ convinced him that such a principle ought not to be universally admitted, although a cluster of stars may undoubtedly assume a nebulous appearance when it is too remote for us to discern the stars of which it is composed. When he perceived that additional light had no effect in resolving certain nebulæ into stars, he was forced to the conclusion that, though milky nebula may contain stars, yet there are also nebulosities which are not composed of them nor immediately connected with them.

Hence astronomers have been constrained to admit the existence of a certain species of fine luminous matter, distinct

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