light at their interior edges, where they enclose and surround a sort of three-forked rift, or vacant area, abruptly and uncouthly crooked, and quite void of nebulous light. A beautiful triple star is situated precisely on the edge of one of these nebulous masses just where the interior vacancy forks out into two channels. A fourth nebulous mass spreads like a fan or downy plume from a star at a little distance from the triple nebula.

(889.) Nearly adjacent to the last described nebula, and no doubt connected with it, though the connexion has not yet been traced, is situated the 8th nebula of Messier's Catalogue. It is a collection of nebulous folds and masses, surrounding and including a number of oval dark vacancies, and in one place coming up to so great a degree of brightness, as to offer the appearance of an elongated nucleus. Superposed upon this nebula, and extending in one direction beyond its area, is a fine and rich cluster of scattered stars, which seem to have no connexion with it, as the nebula does not, as in the region of Orion, show any tendency to congregate about the stars.

(890.) The 19th nebula of Messier's Catalogue, though some degrees remote from the others, evidently belongs to this group. Its form is very remarkable, consisting of two loops like capital Greek Omegas, the one bright, the other exceedingly faint, connected at their bases by a broad and very bright band of nebula, insulated within which by a narrow comparatively obscure border, stands a bright, resolvable knot, or what is probably a cluster of exceedingly minute stars. A very faint round nebula stands in connexion with the upper or convex portion of the brighter loop.

(891.) The nebulous group of Cygnus consists of several large and irregular nebulæ, one of which passes through the double star k Cygni, as a long, crooked, narrow streak, forking out in two or three places. The others *, observed in the first instance by Sir W. Herschel and by the author of this work as separate nebulæ, have been traced into connexion by Mr. Mason, and shown to form part of a curious and intricate nebulous system, consisting, 1st, of a long, narrow, curved,

*R. A. 20h 49m 20, N. P.D. 58° 27'.

and forked streak, and 2dly, of a cellular effusion of great extent, in which the nebula occurs intermixed with, and adhering to stars around the borders of the cells, while their interior is free from nebula, and almost so from stars.

(892.) The Magellanic clouds, or the nubecula (major and minor), as they are called in the celestial maps and charts, are, as their name imports, two nebulous or cloudy masses of light, conspicuously visible to the naked eye, in the southern hemisphere, in the appearance and brightness of their light not unlike portions of the Milky Way of the same apparent size. They are, generally speaking, round, or somewhat oval, and the larger, which deviates most from the circular form, exhibits the appearance of an axis of light, very ill defined, and by no means strongly distinguished from the general mass, which seems to open out at its extremities into somewhat oval sweeps, constituting the preceding and following portions of its circumference. A small patch, visibly brighter than the general light around, in its following part, indicates to the naked eye the situation of a very remarkable nebula (No. 30. Doradûs of Bode's catologue), of which more hereafter. The greater nubecula is situated between the meridians of 4h 40m and 6h 0m and the parallels of 156° and 162° of N. P. D., and occupies an area of about 42 square degrees. The lesser, between the meridians 0h 28m and 1h 15m and the parallels of 162° and 165° N. P. D., covers about ten square degrees. Their degree of brightness may be judged of from the effect of strong moonlight, which totally obliterates the lesser, but not quite the greater.

(893.) When examined through powerful telescopes, the constitution of the nubeculæ, and especially of the nubecula major, is found to be of astonishing complexity. The general ground of both consists of large tracts and patches of nebulosity in every stage of resolution, from light, irresolvable with 18 inches of reflecting aperture, up to perfectly separated stars like the Milky Way, and clustering groups sufficiently insulated and condensed to come under the designation of irregular, and in some cases pretty rich clusters. But be

• It is laid down nearly an hour wrong in all the celestial charts and globes.

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sides those, there are also nebulæ in abundance, both regular and irregular; globular clusters in every state of condensation; and objects of a nebulous character quite peculiar, and which have no analogue in any other region of the heavens. Such is the concentration of these objects, that in the area occupied by the nubecula major, not fewer than 278 nebula and clusters have been enumerated, besides 50 or 60 outliers, which (considering the general barrenness in such objects of the immediate neighbourhood) ought certainly to be reckoned as its appendages, being about 6 per square degree, which very far exceeds the average of any other, even the most crowded parts of the nebulous heavens. In the nubecula minor, the concentration of such objects is less, though still very striking, 37 having been observed within its area, and 6 adjacent, but outlying. The nubeculæ, then, combine, each within its own area, characters which in the rest of the heavens are no less strikingly separated,-viz., those of the galactic and the nebular system. Globular clusters (except in one region of small extent) and nebula of regular elliptic forms are comparatively rare in the Milky Way, and are found congregated in the greatest abundance in a part of the heavens, the most remote possible from that circle; whereas, in the nubeculæ, they are indiscriminately mixed with the general starry ground, and with irregular though small nebulæ.

(894.) This combination of characters, rightly considered, is in a high degree instructive, affording an insight into the probable comparative distance of stars and nebulæ, and the real brightness of individual stars as compared one with another. Taking the apparent semidiameter of the nubecula major at 3°, and regarding its solid form as, roughly speaking, spherical, its nearest and most remote parts differ in their distance from us by a little more than a tenth part of our distance from its center. The brightness of objects situated in its nearer portions, therefore, cannot be much exaggerated, nor that of its remoter much enfeebled, by their difference of distance; yet within this globular space, we have collected upwards of 600 stars of the 7th, 8th, 9th, and 10th magnitudes, nearly 300 nebulæ, and globular and other clusters,

of all degrees of resolubility, and smaller scattered stars innumerable of every inferior magnitude, from the 10th to such as by their multitude and minuteness constitute irresolvable nebulosity, extending over tracts of many square degrees. Were there but one such object, it might be maintained without utter improbability that its apparent sphericity is only an effect of foreshortening, and that in reality a much greater proportional difference of distance between its nearer and more remote parts exists. But such an adjustment, improbable enough in one case, must be rejected as too much so for fair argument in two. It must, therefore, be taken as a demonstrated fact, that stars of the 7th or 8th magnitude and irresolvable nebula may co-exist within limits of distance not differing in proportion more than as 9 to 10, a conclusion which must inspire some degree of caution in admitting, as certain, many of the consequences which have been rather strongly dwelt upon in the foregoing pages.

(895.) Immediately preceding the center of the nubecula minor, and undoubtedly belonging to the same group, occurs the superb globular cluster, No. 47. Toucani of Bode, very visible to the naked eye, and one of the finest objects of this kind in the heavens. It consists of a very condensed spherical mass of stars, of a pale rose colour, concentrically enclosed in a much less condensed globe of white ones, 15′ or 20′ in diameter. This is the first in order of the list of such clusters in Art. 867.

(896.) Within the nubecula major, as already mentioned, and faintly visible to the naked eye, is the singular nebula (marked as the star 30 Doradûs in Bode's Catalogue) noticed by Lacaille as resembling the nucleus of a small comet. It occupies about one-500th part of the whole area of the nubecula, and is so satisfactorily represented in plate V., fig. 1., as to render further description superfluous.

(897.) We shall conclude this chapter by the mention of two phænomena, which seem to indicate the existence of some slight degree of nebulosity about the sun itself, and even to place it in the list of nebulous stars. The first is that called the zodiacal light, which may be seen any very clear

evening soon after sunset, about the months of March, April, and May, or at the opposite seasons before sunrise, as a cone or lenticularly-shaped light, extending from the horizon obliquely upwards, and following generally the course of the ecliptic, or rather that of the sun's equator. The apparent angular distance of its vertex from the sun varies, according to circumstances, from 40° to 90°, and the breadth of its base perpendicular to its axis from 8° to 30°. It is extremely faint and ill defined, at least in this climate, though better seen in tropical regions, but cannot be mistaken for any atmospheric meteor or aurora borealis. It is manifestly in the nature of a lenticularly-formed envelope, surrounding the sun, and extending beyond the orbits of Mercury and Venus, and nearly, perhaps quite, attaining that of the earth, since its vertex has been seen fully 90° from the sun's place in a great circle. It may be conjectured to be no other than the denser part of that medium, which, we have some reason to believe, resists the motion of comets; loaded, perhaps, with the actual materials of the tails of millions of those bodies, of which they have been stripped in their successive perihelion passages (Art. 566.). An atmosphere of the sun, in any proper sense of the word, it cannot be, since the existence of a gaseous envelope propagating pressure from part to part; subject to mutual friction in its strata, and therefore rotating in the same or nearly the same time with the central body; and of such dimensions and ellipticity, is utterly incompatible with dynamical laws. If its particles have inertia, they must necessarily stand with respect to the sun in the relation of separate and independent minute planets, each having its own orbit, plane of motion, and periodic time. The total mass being almost nothing compared to that of the sun, mutual perturbation is out of the question, though collisions among such as may cross each other's paths may operate in the course of indefinite ages to effect a subsidence of at least some portion of it into the body of the sun or those of the planets.

(898.) Nothing prevents that these particles, or some among them, may have some tangible size, and be at very great distances from each other. Compared with planets