442 
ME. W. HUGGINS ON THE SPECTEA OF SOME OF THE NEBULiE. 
is not uniform, but is evidently crossed either by lines of absorption or by bright 
lines. 
[No. 428. 55 Androm. R.A. l h 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. E.A. 4 1 ' 7 m 50 s -8. N.P.D. 103° 5' 32" -2. Very bright clus- 
ter.] In Eridanus. The spectrum could be traced from the orange to about the blue. 
No indication 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 2., 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 refrangibili- 
ties through an atmosphere which intercepts 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 vapour. 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 nebulae, 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 nebulae, which are scarcely in 
accordance with the opinion that they are clusters of stars. 
Sir John ITerschel 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 uni- 
formly 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 con- 
stitution to be either that of a hollow spherical shell or of a flat disk presented to us 
(by a highly improbable coincidence) in a plane precisely perpendicular to the visual 
ray”f. This absence of condensation admits of explanation, without recourse to the 
supposition of a shell or of a fiat disk, if we consider them to be masses of glowing gas. 
For supposing, as we probably must do, that the whole mass of the gas is luminous, 
yet it would follow, by the law which results from the investigations of Kirchhoff, 
that the light emitted by the portions of gas beyond the surface visible to us, would 
* “ Looked at eight times, but saw no nebulous atmosphere.” — Lord Eosse; Philosophical Transactions, 
1861, p. 712. 
f Outlines of Astronomy, 7th edit. p. 646. 
