base of about 4°, and a height of about 51°, reaching downwards from, the apex (with a break, however, at σ), almost as far as vm. 4 is a singular nebula, faintly visible to the naked eye, situated within the limits of the nubecula major; it was noticed by La Caille as resembling the nucleus of a comet, and is one of the most singular and extraordinary objects in the heavens. 5 is a very large nebula surrounding the star 7 Argûs, and occupying a space equal to about 5 times the area of the Moon. Sir J. Herschel, who carefully examined this object when at the Cape of Good Hope in 1833 and following years, says that "viewed with an 18-inch reflector no part of this strange object shews any sign of resolution into stars, nor in the brightest and m See Struve, Month. Not. R.A.S., vol. xvii. pp. 225-30: W. C. Bond, Mem. Amer. Acad., vol. iii. N.S., p. 87: Sir J. Herschel, Res. Ast. Obs., pp. 25-32; Outlines of Ast., p. 650: Secchi, Month. Not. R.A.S., vol. xviii. p. 8: G. P. Bond, ibid., vol. xxi. p. 203: Liapounov, ibid., vol. xxiii. p. 228-for various remarks on this nebula. most condensed portion, adjacent to the singular oval vacancy in the middle of the figure, is there any of that curdled appearance or that tendency to break up into bright knots with intervening darker portions, which characterise the nebula of Orion, and indicate its resolvability. It is not easy for language to convey a full impression of the beauty and sublimity of the spectacle which this nebula offers, as it enters the field of the telescope (fixed in R. A.) by the diurnal motion, ushered in as it is by so glorious and innumerable a procession of stars, to which it forms a sort of climax n." Some recent observations on a point of great importance concerning this nebula will be alluded to hereafter. 6. The nebula surrounding « Crucis is described by Sir J. Herschel as one of the most beautiful objects of its class: it consists of about 110 stars from the 7th magnitude downwards, n See Res. Ast. Obs., pp. 32-47. 8 of the more conspicuous of them being coloured various shades of red, green, and blue, so as to give the whole the appearance of a rich piece of jewellery. 7 is visible to the naked eye, and resembles a tail-less comet: its brilliancy is about equal to that of a 44-magnitude star, but, "viewed in a telescope, it appears as a globe fully 20' in diameter, very gradually increasing in brightness to the centre, and composed of innumerable stars of the 13th and 15th magnitudes "." 8 is the chief member of an important group of nebula. "One of them (H 1991) is singularly trifid, consisting of 3 bright and irregularly formed nebulous masses, graduating away insensibly externally but coming up to a great intensity of light at their interior edges, where they enclose or 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 P." 9. "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 Fig. 173. 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, shew any tendency to congregate about the stars." 10 is usually termed the "Horse-shoe nebula " from the peculiarity of its shape this, however, merely applies to the THE NEBULA 27 M CLYPEI SOBIESKII. most prominent portion, for there (Chambers.) is an important outlier; and when this is seen, and also the bright lens-like band which unites See Res. A st. Obs., Sir J. Herschel, Outlines of Ast., p. 653. |
