Clusters and Nebulce. 349 



the gigantic instruments of modern times, nor does the General 

 Catalogue refer to them as resolvable. The strength of their 

 light might have been thought an indication of nearness, 

 and consequent resolvability, had we not already learned the 

 inadequacy of any such test ; and it is not unlikely that the 

 following assertion of Sir J. Herschel may find its application 

 here: — " There is one circumstance which deserves especial 

 remark, and which, now that my own observation has extended 

 to the nebula? of both hemispheres, I feel able to announce 

 with confidence as a general law, viz., that the character of 

 easy resolvability into separate and distinct stars is almost en- 

 tirely confined to nebulas deviating but little from the spherical 

 form; while, on the other hand, very elliptic nebulas, even 

 large and bright ones, offer much greater difficulty in this 

 respect. The cause of this difference must, of course, be con- 

 jectural, but, I believe it is not possible for any one to review 

 seriatim the nebulous contents of the heavens without being- 

 satisfied of its reality as a physical character. Possibly the 

 limits of the conditions of dynamical stability in a spherical 

 cluster may be compatible with less numerous and comparatively 

 larger individual constituents than in an elliptic one." When 

 these most interesting remarks were penned, in 1845, the 

 great reflector of the Earl of Rosse had just been brought into 

 action, and its extraordinary disclosures had led the illustrious 

 writer to incline to the idea that all nebulous matter might be 

 ultimately proved, or at least fairly inferred, to be of a starry 

 nature. No material advance, however, has since been made 

 in this direction, and the question is by no means set at rest. 

 Even if it had been previously considered as settled, it would 

 have been reopened by the discoveries of Huggins. If the not 

 improbable assumption may be admitted, that these two 

 nebulas are at about an equal distance from the earth, they 

 must be comparatively near one another; each must form a 

 magnificent object in the other's firmament ; and if they are 

 really of a starry nature their component suns must shine with 

 distinct and impressive splendour. 81 M. especially, even if no 

 more of its extent were perceptible there than here — a most 

 unlikely supposition — would occupy perhaps a space equal to 

 the breadth of ten full moons with its denser brightness — pos- 

 sibly twice as much with its outlying rays. 81 M. is No. 1949, 

 its neighbour 1950 of the General Catalogue. 



Reference having been repeatedly made to the new Cata- 

 logue of Nebulas and Clusters of Stars, by Sir J. Herschel, a 

 short description of it may not be unwelcome here. This admi- 

 rable production, the result of most accurate and unwearied 

 research both in the heavens and among the labours of other 



