EARL ROSSE’S OBSERVATIONS ON THE NEBULA. 
507 
either physically or optically ; in the latter case it is not unlikely that in a faint nebula 
they might be seen separate with an instrument of great aperture, while in the 
brighter and more closely packed nebula they were blended together, owing to imper- 
fect definition, arising out of the state of the air, or instrument. As an example, the 
dumb-bell is a bright nebula : on three exceedingly fine nights succeeding each other 
at short intervals, the stars in the brighter parts of the nebula were better shown 
with 3 feet aperture than they have since been with 6 feet. Very fine nights, when 
the air seems to set no limits to magnifying power, are extremely rare, and the dumb- 
bell has not been seen with the great instrument on such nights. On the other 
hand, on all ordinary nights, a variety of details are shown by the great instrument 
which were not seen on the finest nights with the smaller instrument. There is 
another fact I may perhaps add, that while high magnifying power brings out minute 
stars it extinguishes faint nebulosity. The optical reason is obvious ; but in sketching 
the dumb-bell nebula in 1845 that fact was overlooked, and but one eye- piece was 
used, a very high one ; had there been a low one also used the sketch would have 
been more complete. To return to the annular nebulae. The five planetary nebulae 
we have ascertained to be annular, are as follows : 464, Plate XXXVIll. fig. 12, has 
two stars within it; 2075 has one star a little following the centre; 2241, Plate 
XXXVlII. fig. 13, has no star, but is surrounded with a faint external annulus; 
2050 has a perforation not round nor quite symmetrical with the star ; 838, Plate 
XXXVII. fig. 11, has two stars and two perforations. In no instance is the central 
opening quite dark. The planetary nebula, 2047, is marked in our journal as annular, 
but the observation is without date and other particulars, and therefore I do not 
consider it altogether trustworthy. In 2098, Plate XXXVIll. fig. 14, another 
planetary nebula, we have not detected any perforation, but it has ansae, which pro- 
bably indicate a surrounding nebulous ring seen edgeways, just as 450, Plate XXXVIll. 
fig. 15, has apparently a nebulous ring seen on the flat; and if the annular nebulae 
are really hollow shells, the nebulous ring would cover the comparatively transpa- 
rent centre ; 365 and 2037 have never been observed. 
Passing from the annular nebulae to the nebulous stars, there are two objects well- 
worthy of especial notice. 
Sir John Herschel very accurately describes a nebulous star thus : — “ A sharp and 
brilliant star concentrically surrounded by a perfectly circular disc or atmosphere of 
faint light, in some cases dying away insensibly on all sides, in others almost suddenly 
terminated*.” No. 450 of Sir John Herschel’s Catalogue is one of these nebulous 
stars, and is there thus described: — ‘‘A star of the 8th magnitude, exactly in the 
centre of an exactly round and bright atmosphere, 25 " diameter. The star is quite 
stellar, not a mere nucleus. Another star, 8th magnitude, distant 100", and about 
85° n p, has no such atmosphere. — A most remarkable object.” 
Plate XXXVIll. fig. 15 represents this wonderful object as seen with the 6-feet 
telescope. It has been several times examined, and as yet we have not seen the 
* Outlines of Astronomy, p. 605. 
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