506 
EARL R'OSSE’S OBSERVATIONS ON THE NEBULA. 
observed, but they are still marked doubtful in our working list, having been seen 
when the air was not very transparent; 51 Messier, Plate XXXV. fig. l,is the most 
conspicuous object of that class. 
The question may perhaps suggest itself whether there is not something in the aspect 
of a spiral nebula, which forces upon us the conviction that it is a system with an 
organization quite different from that of any known cluster. The only answer I am 
enabled to give to that question is, that in the exterior stars of some clusters there ap- 
pears to be a tendency to an arrangement in curved branches, which cannot well be 
unreal, or accidental. Nos. 480, 1916, 1968, 1972, are the objects in which I observe 
that peculiarity noted down in our list of observations as suspected. As to 1968, Sir 
John Herschel uses the following words in his Catalogue, “ has hairy-looking curvi- 
linear branches.” Careful drawings based on measurements would settle the ques- 
tion, whether the suspected curvilinear distribution of the stars is real or not ; this 
would also perhaps settle another question of interest, whether the distribution of the 
stars in these objects is reconcileable with the hypothesis of an equal distribution of 
the stars of the system ; as yet however there has not been time to make the required 
measurements. In passing from the spiral to the regular annular nebulae, we perceive 
we are at once engaged with objects of a very different character ; still here even there 
seems to be something like a connecting link ; the great round planetary nebula, H 838, 
Plate XXXVII. fig. 11, with a double perforation appears to partake of the structure 
both of the annular and spiral nebulae. There were but two annular nebulae known in 
the northern hemisphere when Sir John Herschel s Catalogue was published ; now 
there are seven, as we have found that five of the planetary nebulae are really annular. 
Of these objects, the annular nebula in Lyra is the one in which the form is by far 
the most easily recognized. I have not yet sketched it with the 6-feet instrument, 
because I have never seen it under favourable circumstances : the opportunities of 
observing it well on the meridian are comparatively rare owing to twilight. It was 
however observed seven times in 1848 and once in 1849. The only additional par- 
ticulars I collect from the observations, are that the central opening has considerably 
more nebulosity in it than it appeared to have with the 3-feet instrument, and 
that there is one pretty bright star in it, s.f. the centre, and a few other very minute 
stars. In the sky round the nebula and near it there are several very small stars 
which were not before seen, and therefore the stars in the dark opening may possibly 
be merely accidental. In the annulus, especially at the extremities of the minor axis, 
there are several minute stars, but there was still much nebulosity not seen as 
distinct stars. 
The other annular nebula of Herschel’s Northern Catalogue is a much fainter 
object; it has been observed but once with the large instrument, August 1, 1848; 
but the evidence of resolution appears to have been more complete ; many stars were 
seen in the annulus ; one of them was very conspicuous. That a faint nebula should 
be more easily resolvable than a bright one is not unusual, neither is it contrary to 
probability ; faintness may be owing to distance, or to a wider separation of the stars. 
