OF ARTS AND SCIENCES. 229 



The general aspect of the greater part of the nebula is thei'efore that 

 of an assemblage of curved wisps of luminous matter, which, branching 

 outward from a common origin in the bright masses in the vicinity of 

 the Trapezium, sweep towards a southerly direction, on either side of an 

 axis passing through the apex of the Regio Huygeniana, nearly in the 

 angle of position 180°. About twenty of these convolutions have been 

 distinctly traced, while others giving a like impression are too faint or 

 too intricate to be subjected to precise description. It may therefore be 

 properly classed among " the spiral nebulfe," under the definition given 

 by their first discoverer. Lord Rosse; including in the term all objects 

 in which a curvilinear arrangement, not consisting of I'egular re-enter- 

 ing curves, may be detected. 



That the existence of this feature in the great nebula of Orion should 

 have hitherto escaped notice, after the many careful scrutinies to which 

 it has been subjected, with the help of the largest instruments and the 

 most skilful observers, may seem scarcely credible ; a few words of 

 explanation on this point will not therefore be amiss. It is to be 

 ascribed partly to the confusing effect produced by the crossing and 

 intersection of the principal strice and of their offsets, which the eye 

 cannot unravel without the aid of some clew to their mutual relation 

 and significance ; and partly also to the faintness of some of the details, 

 which are, nevertheless, very essential features in a correct apprehen- 

 sion of its structure, supplying, as they do, what would otherwise appear 

 as breaks of continuity, and assisting materially in the recognition of 

 a principle of regularity pervading the whole structure. Until the law 

 of relation and continuity in the several parts of such an object is en- 

 tei-tained in the mind, it must remain an incohei'ent, confused assem- 

 blage of material, having no orderly or connected arrangement. 



The change from the previous notion of its configuration is not more 

 considerable than that which took place with reference to the celebrated 

 nebula 51 Messier, in which the original discovery of the spiral arrange- 

 ment was made. This object had been subjected to a careful examina- 

 tion and description by both the Herschels, but neither their drawings 

 nor descriptions furnished the slightest intimation of a spiral structure. 

 It deserves particular notice, too, that there was no want of sufficient 

 optical power to exhibit the appearance in question ; for the spirality of 

 51 Messier is seen with perfect distinctness in a refractor of 15 inches' 

 aperture, and must certainly be within reach of the twenty-foot Her- 

 schelian reflectors. Nor can it for a moment be tboujrht that tlie earlier 



