440 FORMS OF NEBULAE. [SECT, xxxvii. 



circular, and seen obliquely like the central nebula itself, 

 would have a diameter somewhat more than four times the 

 latter, a stupendous system doubtless, but of which the 

 reality can hardly be supposed improbable. 



There appears to be some connexion between ellipticity 

 of form and difficulty of resolution, for spherical clusters are 

 in general easily resolved into their component stars, while 

 there is scarcely an instance of an elliptical cluster yielding 

 even to a very high optical power. Vast masses of the 

 nebulae have never been resolved; the great nebula of 

 Andromeda and the first of Sir William Herschel's 5th class, 

 discovered by Miss Caroline Herschel, have hitherto resisted 

 every power that has been applied to them. Lord Ross's 

 great telescope has resolved parts of the nebula of Orion, 

 and various others which had not yielded to instruments of 

 less power ; it enables the astronomer to penetrate farther 

 into space, and shows objects with greater clearness than 

 any other. But, excellent as this instrument is, thousands 

 of nebulae are not to be resolved even by it. Those who 

 imagine that any work of man can resolve all the nebulous 

 matter in the heavens must have a very limited idea of the 

 extent and sublimity of creation. 



Innumerable nebulae in both hemispheres take the form 

 of clusters of stars, but are totally different from the globular 

 clusters, inasmuch as they are of irregular form and follow 

 no uniform law of condensation. Many are of exquisite 

 beauty, as that round a Crucis, which, though consisting of 

 only a hundred and ten stars, is like a piece of fancy 

 jewellery, from the colours of the stars, which are greenish 

 white, green, blueish green, and red. Many of these clusters 

 contain thousands of stars, and are frequently in the 

 poorer parts of the sky, as if in the course of ages the stars 

 had been attracted towards a centre. 



The existence of every degree of ellipticity in the nebulae 

 from long lenticular rays to the exact circular form and 

 of every shade of central condensation, from the slightest 



