system, otherwise the centre of it would not be less than 6000 times the distance of Sirius, and that it is possibly much underrated by supposing it only 600 times the distance of that star. "Some of these round nebulæ have others near them, perfectly similar in form, colour, and the distribution of stars, but of only half the diameter; and the stars in them seem to be doubly crowded, and only at about half the distance from each other. They are indeed so small as not to be visible without the utmost attention. I suppose these miniature nebula to be at double the distance from the first. An instance equally remarkable and instructive is a case where, in the neghbourhood of two such nebulæ as have been mentioned, I met with a third similar, resolvable, but much smaller and fainter nebula. The stars of it are no longer to be perceived; but a resemblance of colour with the former two, and its diminished size and light, may well permit us to place it at full twice the distance of the second, or about four or five times the distance of the first; and yet the nebulosity is not of the milky kind, nor is it so much as difficultly resolvable or colourless. Now in a few of the extended nebulæ, the light changes gradually, so as from the resolvable to approach to the milky kind; which appears to me an indication that the milky light of nebula is owing to their much greater distance. A nebula, therefore, whose light is perfectly milky, cannot well be supposed to be at less than six or eight thousand times the distance of Sirius; and though the numbers here assumed are not to be taken otherwise than as very coarse estimates, yet an extended nebula which in an oblique situation, where it is possibly foreshortened by one half, two thirds, or three fourths of its length, subtends a degree or more in diameter, cannot be otherwise than of a wonderful magnitude, and may well OUTVIE OUR MILKY WAY IN GRANDEUR.' It appears to be a very natural conclusion, that the nebulæ which are perfectly similar in form, colour, and the distribution of stars, but only of half the diameter, and the stars doubly crowded, are about double the distance from the first. And if the distance of the larger nebulæ, whose stars are distinctly seen, be at least 600 times the distance of Sirius, as there is every reason to believe, then the distance of those which are only half the diameter must be about 1200 times the distance of that star; that is, at the very least, 24.000,000,000,000,000, or twenty-four thousand billions of miles. But the nebula whose light is "perfectly milky," or so far removed from us that the stars of which they are composed cannot be separately distinguished, may be justly considered as seven thousand times the distance of Sirius, or, in numbers, 168,000,000,000,000,000, or one hundred and sixty-eight thousand billions of miles! a distance of which we can have no distinct conception. Light, notwithstanding its amazing velocity, would be nearly thirty thousand years ere it could fly from such nebula to the earth; and a cannon ball, with its utmost velocity, would require more than thirty-eight thousand millions of years before it could move over an equal space. Since the distance of these nebulæ is so immense, and since those which are among the largest and nearest are found by actual observation to be composed of countless numbers of stars, leaving us no room to doubt that the most distant are also immense systems of stars, how great must be the magnitude, and how inexpressible the grandeur, of the numerous luminaries of which they are composed! I have stated above that more than three thousand nebula have already been discovered, and whose places in the heavens have been accurately determined, so that those who have access to powerful telescopes may have an opportunity of observing the greater part of them. From all the observations made by Sir W. Herschel, he is of opinion that our nebula, or the Milky Way, is not the most considerable in the universe; and he points out some very remarkable nebula which in his opinion cannot be less, but are probably much larger, than that of which our own sun and system form a part. Now, on these grounds let us consider what must be the extent and magnitude of only the visible universe. Supposing the number of stars composing the Milky Way to be ten millions, which is only half the number formerly assigned (p. 146), and that each of the nebulæ at an average contains the same number; supposing, farther, that only two thousand of the three thousand nebulæ are resolvable into clusters of stars, and that the other thousand are masses of shining fluid not yet condensed into distinct luminous globes; the number of stars or suns comprehended in that portion of the firmament which is within the reach of our telescopes would be 20,000,000,000, or twenty thousand millions, which is twenty millions of times the number of all the stars visible to the naked eye. Great as this number is, and magnific nt and overpowering as the ideas are which it suggests of the extent of creation, yet these vast assemblages of systems may be no more than as a single nebula to the whole visible firmament, or even as a grain of sand to the whole earth, compared with what lies beyond the range of human vision, and is hid from mortal eye in the boundless and unexplored region of immensity! Beyond the boundaries of all that will ever be visible to the inhabitants of our globe, an infinite region exists, in which we have every reason to believe the Deity sits enthroned in all the grandeur of his overflowing goodness and omnipotence, presiding over innumerable systems, far surpassing in magnificence what "eye hath yet seen" or the most brilliant intellect can conceive. For we ought never for a moment to surmise that the operations of Almighty Power are exhausted at the point where the efforts of genius and art can no longer afford us assistance in tracing the footsteps of the Divinity throughout the mysterious regions of infinitude; nor should we ever suppose that man, placed on such a diminutive ball as the earth, and furnished with powers of so limited a nature as those with which he is now invested, will ever be able to grasp the dominions of Him who fills immensity with his presence, and "whose ways are past finding out." SECTION II.-On the various kinds of Nebula. I have already alluded to the different shapes or forms of nebulæ. These objects, on account of their appearing with different degrees of lustre, and assuming a great variety of shapes and modifications, have been arranged into different classes. 1. The first class is that of clusters of stars, in which the separate stars are clearly distinguished by good telescopes. This class is again divided into globular clusters, or those which appear of a roundish form, and somewhat compressed towards the centre; and irregular clusters, or those which are neither circular nor elliptical, but of a somewhat indefinite or angular form. These last are generally less rich in stars, and less condensed towards the centre, and are likewise less definite in their outline, so that their termination in many cases cannot be distinctly perceived. In some of them the stars are nearly all of the same size, in others extremely different; and "it is no uncommon thing," says Sir J. Herschel, |