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 nebulae which occur 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 Lyrse ; 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 nebulae 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 M 94, 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 having faint nebulosity within them. 



VOL. III. L 



