Among these are objects so surprising, that I shall earnestly desire to see my observations verified by the powerful instruments (if sufficiently so) which are now become common in the hands of observers." More than 4000 have now been observed and catalogued.

Taking a favourable night in spring or autumn, a practised eye may discern a feeble speck between and Herculis, two stars of the third magnitude north and south of each other, in that constellation, being about 22° nearly due west of Vega. This speck is the thirteenth nebula of Messier's list, described by him as nebuleuse sans étoiles. It was observed by Halley in 1714, who remarks, "This is but a little patch, but it shows itself to the naked eye when the sky is serene, and the moon absent." Employing a common telescope, it assumes the appearance of a small and faint cometary body, of a globular shape; but using an instrument of first-rate power, it resolves into a mass of stars, whose number must be enormous, but apparently so closely wedged together, owing to their remoteness, as to present the little indivisible streak of light which is scarcely perceptible

without optical aid. The cut represents this object as seen in a reflector of 18 inches aperture, and 20 feet focal length. It is impossible, says an assiduous observer, to give a fitting representation of this magnificent cluster. Perhaps no one ever saw it for the first time through a large telescope, without uttering a shout of wonder. The heavens, as seen from a sun of this astral system, near its centre, must present a most gorgeous appearance. In all directions, innumerable stars of all magnitudes will be seen, forming a spectacle such as would be presented by our heavens, in case the Milky Way were expanded to cover the entire celestial sphere. Such spherical stellar clusters are common, the individuals of each being no doubt separated from one another by as wide a gulf as that which exists between our sun and the nearest star, their apparent contiguity and compression to us arising from their immeasurable distance.

It is inferred from the appearance presented by many clusters, that the components of each are bound together by mutual relationships, and constitute a particular assemblage of stars governed by internal laws peculiar to itself, though corresponding generally with those which prevail in other sidereal systems. The common occurrence of the globular shape, and of great central condensation, the light there running up into an unbroken blaze, may perhaps be accepted as evidence of the attraction of gravitation. It is striking to catch a glimpse of a law with which we are so familiar-the law that

unites the atoms that compose the earth, forms every rain-drop, and moulds the tear that trickles down the cheek of sorrow-in prevailing operation millions of leagues away from our terrestrial residence, binding together in spherical masses whole sidereal systems. Such a fact, however, commonly suggests no further remark than that the laws of nature everywhere prevail, and with this, thought in general ends. But "what," says Paley, "do we mean by the laws of nature, or by any law? Effects are produced by power, not by laws. A law cannot execute itself. A law refers us to an agent." An irresistible conviction is forced upon us, of the universal agency, and, consequently, the omnipresence of one Lawgiver, by the universal presence and execution of kindred laws; and confessedly incomprehensible as is the modus of His operation, it would be not more irreligious to stumble at this than unphilosophical, considering the immense amount of things of which we have certain evidence that they are, without having any glimpse as to how they are. We cannot at all understand the physical agency of the Deity; but paying deference to the strong facts of nature, we are led to the conclusion that He

"Lives through all life, extends through all extent,
Spreads undivided, operates unspent."

The conclusions are marvellous that are forced upon us by these objects. Here we have firmaments or clusters, insulated in space, each constituting a sidereal family equal to that to which our sun belongs. "It would be a vain task," says the highest authority upon this subject, "to attempt to count the stars in one of these globular clusters. They are not to be reckoned by hundreds; and on a rough calculation, grounded on the apparent intervals between them at the borders (where they are seen not projected on each other), and the angular diameter of the whole group, it would appear that many clusters of this description must contain, at least, ten or twenty thousand stars, compacted and wedged together in a round space, whose angular diameter does not exceed eight or ten minutes; that is to say, in an area not more than a tenth part of that covered by the moon. Perhaps it may be thought to savour of the gigantesque to look upon the individuals of such a group of stars like our own, and their mutual distances, as equal to those which separate our sun from the nearest fixed star: yet when we consider that their united lustre affects the eye with a less impression of light than a star of the fifth or sixth magnitude (for the largest of these clusters is barely visible to the naked eye), the idea we are thus compelled to form of their distance from us may render even such an estimate of their dimensions familiar to our imagination; at all events, we can hardly look upon a group thus insulated, in seipso totus, teres, atque rotundus, as not forming a system of a peculiar and definite character."

But the globular form, though common, is by no means unvarying. There are oval shapes, while some are of very irregular outline, and present a fantastic appearance. The 30 Doradûs, as sketched at Paramatta by Mr Dunlop, and examined by Sir John Herschel at the Cape of Good Hope, resembles a number of loops, or a kind of "true lover's knot" formed by a bunch of ribbons. An angular-shaped mass appears in the Twins, on a line drawn from Pollux to the middle of Orion's belt, discovered by Herschel in 1783. Another, in the form of a distant flight of wild-fowl, discovered by Kirch in 1681, is on the shield which Hevelius framed among the stars in honour of John Sobieski, the deliverer of Vienna from the Turks.

One of the most conspicuous of these objects, called the "transcendently beautiful queen of the nebulæ," and the oldest known, appears below the girdle of Andromeda. It is visible to the naked eye in the absence of the moon, and has often been mistaken for a

comet. A notice of it occurs as early as the commencement of the tenth century. The first telescopic view was obtained by Simon Marius, 15th December 1612, who compared it to a candle shining through a horn; that is, a diluted light, increasing in density towards

a centre. This nebula is of lenticular shape, and forms nearly a right-angled triangle with Almaach and Mirac, the two principal stars of Andromeda. A good eye may pick it up on a favourable night, by projecting a line from Sheratan, the second star in Aries, through Mirac, to about 4° beyond. It is about half a degree long, and from 15' to 20' broad. Herschel believed this to be one of the nearest nebulæ in the heavens, though at a distance two thousand times greater than that of Sirius. Notwithstanding the improved optical means of the moderns, it has not been resolved into stars, though no doubt can be entertained of its stellar composition. Numerous telescopic stars appear involved in the glow, but are not supposed to have any connection with it, being interposed between it and our system.

There are examples of nebula presenting circular or slightly oval disks, resembling planets, but with different degrees of definition at the borders. In several instances they appear of "a fine and full blue colour, verging upon green." They are no doubt clusters of stars reduced by mutual proximity and vast distance to the form of planetary disks. Sometimes they are found combined in pairs, like the physically connected double stars;

and if they are to be regarded as two distinct star-systems, each having its own centre of condensation, yet revolving round each other by the tie of gravitation, the imagination can scarcely realise the vastness of the idea suggested.

It is brighter, more diffuse

While generally exhibiting tolerably defined shapes in the depths of space, some of the more considerable nebulæ have a strangely irregular aspect and outline. This is especially the case with reference to the great nebula of Orion, one of the most extraordinary objects in the heavens, for its great extent, inequalities of light and shade, and capricious form. It occurs in the sword-handle of the figure which forms the constellation; and a good eye may discern it without the assistance of a glass. Huygens was the first to describe this object, though Galileo is said to have observed it through his telescope. "Astronomers," says the former, "place three stars close to each other in the sword of Orion: and, when I viewed the middlemost with a telescope in the year 1656, there appeared, in the place of that one, twelve other stars; among these, three that almost touch each other, and four more besides, appeared twinkling as through a cloud, so that the space about them seemed much brighter than the rest of the heavens, which appearing wholly blackish, by reason of the fair weather, was seen as through a certain opening, through which one had a free view into another region which was more enlightened. I have frequently observed the same appearance in the same place without any alteration; so that it is likely that this wonder, whatever it may be in itself, has been there from all time; but I never took notice of any thing like it among the rest of the fixed stars." This nebula, as discerned by the naked eye, exhibits an indefinite, foggy appearance. and strange, when a telescope is used; but the whole light and power of Herschel's fortyfeet reflector could not resolve it into distinct stars. "This highly interesting object," he states, "engaged my attention in the beginning of the year 1774, when, viewing it with a Newtonian reflector, I made a drawing of it; and, having from time to time reviewed it with my large instruments, it may easily be supposed that it was the very first object to which, in February 1787, I directed my forty-feet telescope. The superior light of this instrument showed it of such a magnitude and brilliancy, that, judging from these circumstances, we can hardly have a doubt of its being the nearest of all the nebulæ in the heavens, and, as such, will afford us much valuable information." It seems composed of little flocky masses, or wisps of cloud, adhering to some small stars at its outskirts, and enveloping one with an atmosphere of considerable extent. "I know not," says Sir John Herschel, "how to describe it better than by comparing it to 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 cirrous 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, no appearance of being composed of stars; and their aspect is altogether different from that of the resolvable nebulæ. In the latter, we fancy, by glimpses, that we see stars, or that, could we strain our sight a little more, we should see them but the former suggests no idea of stars, but rather of something quite distinct from them." From a comparison of the descriptions and drawings of this object, since the time of Huygens, great alterations might be inferred. But astronomical delineation was not then sufficiently advanced to render the diagrams at all satisfactory, nor were the instruments sufficiently powerful. The first rigidly accurate representation of it is that by Sir John Herschel, which justifies its familiar name, that of the Fish's Mouth, as it certainly resembles the head and yawning jaws of some monstrous animal, with a kind of proboscis running out from the snout. Its apparent superficial magnitude is rather more than twice that of the moon's disk. The absolute dimensions must be enormous.

:

Such, down to a recent date, were the only ascertained peculiarities of this wondrous From the perfect irresolvableness of this and other nebulæ, together with a milky appearance, it was formerly supposed that a distinction must be drawn between them and

mass.

those of the resolvable class. The latter, with more or less difficulty, were separated by the telescope into stars; the former gave no indication of being similarly constituted when interrogated by the highest instrumental power. Hence arose the famous hypothesis, that a chaotic kind of material exists, occupying extensive spaces, self-luminous and phosphorescent, which presents an endless variety of contour and condensation, resembling in many instances a sheet of fog, but exhibiting in others an aggregation into spherical or oblong This was conceived to furnish a key to the origin of the worlds and systems of worlds disclosed around us-to unveil, likewise, the primitive state and early history of the solar universe-diffused nebulosities having advanced gradually by the mutual attraction of their particles into dense spheroids.

masses.

The theory was premature, for improved telescopic power has largely disproved its data. After looming mysteriously in the sky, the great nebula of Orion yielded to the giant instrument of Lord Rosse, and disclosed its stellar construction. The history of the event is thus given by Dr Nichol :-" About Christmas 1845, I had the pleasure of visiting Parsonstown, and saw the nebula, through that mighty tube. It was-owing to the incompleteness of the instrument and unfavourable weather-the first time that the grand telescope had been directed towards that mysterious object: and though Lord Rosse warned me that the circumstances of the moment would not permit him to regard the decision then given as final, I went in breathless interest to its inspection. Not yet the veriest trace of a star! Looming unintelligible as ever, there the nebula lay; but how brilliant its brighter parts! How much more broken the interior of its mass! How innumerable the streamers now attached to it on every side! How strange, especially that large horn to the north, rising in relief out of the dark skies, like a large cumulus cloud! It was still possible, then, that the nebula might be irresolvable by the loftiest efforts of human art; but doubt continued to remain. Why, in an inquiry like this, the concurrence of every favourable condition is needful to success, may be readily comprehended. It is its aim to discern, singly, a number of sparkling points-small as the point of a needle, and close almost as the particles of a handful of sand; how easy, then, for any unsteadiness in the air, or any imperfection in the instrument, so far to diffuse the light of each that they would merge into each other, and thus become confounded in one mass !" Throughout the winter, the noble owner and constructer of the instrument resolved to seize every favourable opportunity to penetrate, if possible, the constitution of this wonderful object; and at length addressed the following note to Dr Nichol : -"March 19, 1846. In accordance with my promise of communicating to you the result of our examination of Orion, I think I may safely say, that there can be little, if any, doubt as to the resolvability of the nebula. Since you left us, there was not a single night when, in absence of the moon, the air was fine enough to admit of our using more than half the magnifying power the speculum bears; still we could plainly see that all about the trapezium is a mass of stars; the rest of the nebula also abounding with stars and exhibiting the characteristics of resolvability strongly marked.-ROSSE." It has subsequently been shown more fully to consist of an immense irregular assemblage of stars, which were not previously discernible for want of sufficient optical aid. Hence it is morally certain, that all these irresolvable objects are really star-systems, the components of which are not distinguishable by reason of their remoteness, though collectively they gleam across those spaces, the magnitude of which is perfectly confounding.

The different appearances presented by the same nebulæ, when viewed by inferior and more powerful telescopes, is very striking. The following are examples of the same object as seen in Sir John Herschel's instruments and those of Lord Rosse. The Crab Nebula, which the right-hand figure in the cut shows with the strange appendages brought to light by the mirror of Lord Rosse, appeared to Sir John Herschel as a dull ellipse, like