oe 
129 
densed into a ring, although many are also spread over its in- 
terior. Were the centre absent, we should have a ring ne- 
bula ;* and were the line of vision near the plane of this ring 
it would become one of those rays with a bright nucleus and 
parallel band or satellite nebule which oceur so frequently in 
the catalogue. In comparing it with our own sidereal system, 
Dr. R. thinks we should consider the stars visible to the naked 
eye, and the larger telescopic classes as constituting the cen- 
tral cluster, while the Milky Way represents the exterior and 
minuter stars either disposed in an irregular ring or in a stra- 
tum, two of whose dimensions are much greater than the 
third. We have no reason for believing that the comparative 
brightness of stars depends only on their distances ; 61 Cygni 
is not more remote than a Lyre; much less can we assume 
that our stars are uniformly distributed: Orion, the Pleiades, 
Proesepe, the clusters in Perseus, M. 36 and 37, with many 
others, are evidently mere knots of condensation in our imme- 
diate neighbourhood, our peculiar cluster; and it seems a 
mere arbitrary assumption to fancy that, were we transported 
to a remote part of the Milky Way, we should see any thing 
similar to our present sky. 
The nebulz of the third class which were examined seemed 
to differ from this type only by being seen obliquely, and 
therefore projected into ellipses sometimes almost linear. In 
this last case they proved much more difficult of resolution, 
probably from greater optical condensation, and yielded most 
easily towards their minor axes. In these the nucleus of 
brighter stars is sometimes extended like the exterior portion, 
as in 602, which is of considerable length and easily resolved : 
the central part has three knots, of which two are represented 
in fig. 70, all the rest having been invisible. 668 is similar, 
* It is possible that the exterior part of M94, may be merely a circular 
disc of stars: the absence of the central giobe would make this a planetary 
nebula: but it is possible that these differ from the annular only in degree; 
all the latter which he has seen haying faint nebulosity within them. 
VOL, Ill. L 
