

of some of the Nebula, 529 



throughout its length, is not uniform but is evidently crossed 

 either by lines of absorption or by bright lines. 



[No. 428. 55 Androm. R.A. 1^ 44 m 55 s 9. N.P.D. 49° 

 57' 41"*5* Fine nebulous star with strong atmosphere.] The 

 spectrum apparently similar to that of an ordinary star*. 



[No. 826. 2618 h. 26 IV. R.A. 4 h 7 m 50 s -8. N.P.D. 103° 

 5' 32" *2. Very bright cluster.] In Eridanus. The spectrum 

 could be traced from the orange to about the blue. No indica- 

 tion of the bright lines. 



Several other nebulae were observed, but of these the light was 

 found to be too faint to admit of satisfactory examination with 

 the spectrum-apparatus +. 



It is obvious that the nebulae 37 H. IV., 6 %, 73 H. IV., 

 51 H. IV., 1 H. IV., 57 M., 18 H. IV., and 27 M. can no longer 

 be regarded as aggregations of suns after the order to which our 

 own sun and the fixed stars belong. We have in these objects 

 to do no longer with a special modification only of our own type 

 of suns, but find ourselves in the presence of objects possessing 

 a distinct and peculiar plan of structure. 



In place of an incandescent solid or liquid body transmitting 

 light of all refrangibilities through an atmosphere which inter- 

 cepts by absorption a certain number of them, such as our sun 

 appears to be, we must probably regard these objects, or at least 

 their photo-surfaces, as enormous masses of luminous gas or va- 

 pour. For it is alone from matter in the gaseous state that light 

 consisting of certain definite refrangibilities only, as is the case 

 with the light of these nebula?, is known to be emitted. 



It is indeed possible that suns endowed with these peculiar 

 conditions of luminosity may exist, and that these bodies are 

 clusters of such suns. There are, however, some considerations, 

 especially in the case of the planetary nebulas, which are scarcely 

 in accordance with the opinion that they are clusters of stars. 



Sir John Herschel remarks of one of this class, in reference 

 to the absence of central condensation, " Such an appearance 

 would not be presented by a globular space uniformly filled with 

 stars or luminous matter, which structure would necessarily give 

 rise to an apparent increase of brightness towards the centre, in 

 proportion to the thickness traversed by the visual ray. We 

 might therefore be inclined to conclude its real constitution to 



* " Looked at eight times, but saw no nebulous atmosphere." — Lord 

 Rosse, Philosophical Transactions, 1861, p. 712. 



t The author has since observed 31 nebulae and clusters, each of which 

 gives a continuous spectrum. — Proceedings of the Roval Society, vol. xiv. 

 p. 39 ; vol. xv. p. 18. 



