410 AXXULAR NEBULA. SECT. XXXVI. 



division of the limb of the ring into two branches is at once 

 recognised in the bright convolutions of the spiral. The out- 

 lying nebula is connected by a narrow curved band of light with 

 the ring ; the whole is either resolved into stars, or evidently 

 might be with a still higher optical power. With regard to the 

 marvellous nebula in question Lord Eosse observes, that " with 

 each increase of optical power the structure has become more 

 complicated, and more unlike anything that could result from 

 any form of a dynamical law of which we find a counterpart in 

 our s} 7 stem. The connection of the companion with this great 

 nebula, of which there is not the least doubt, adds to the difficulty 

 of forming any hypothesis. It is impossible that such a system 

 could exist without internal movement, to which may be added 

 a resisting medium ; but it cannot be regarded as a case of mere 

 static equilibrium." This is by no means the only instance of a 

 spiral nebula ; Lord Eosse has discovered -several others : some are 

 easily seen others require the highest powers of his telescope. 

 From the numerous offsets that branch from the Milky Way and 

 run far into space, it may possibly partake also of the spiral form. 

 There are seven annular nebulce in the northern hemisphere, 

 since Lord Eosse has discovered that five of the planetary nebula? 

 belong to this class. One of the finest examples of an annular 

 nebula is to be seen midway between /3 and y Lyrje (fig. 2, plate 9). 

 According to Sir John Herschel, it is elliptical in the ratio of 4 to 

 5, and is sharply defined the internal opening occupying about 

 half the diameter. This opening is not entirely dark, but filled 

 with a faint hazy light like fine gauze stretched over a hoop. Its 

 diameter, if it is as far from us as 61 Cygni, must be 1300 times 

 greater than the diameter of the earth's orbit dimensions that 

 are most astounding. Lord Eosse's telescope resolves this object 

 into stars of extreme minuteness, with filaments of stars adhering 

 to its edges and a pretty bright star in its interior. These rings 

 are like hollow shells whose borders seem brighter because the 

 nebulous substance, whatever it may be, is more condensed to 

 appearance than the central part. The other annular nebula in 

 the northern hemisphere described by Sir John Herschel is a 

 small faint object, and more easily resolvable into stars. One of 

 the annular nebulae seen by Lord Eosse is surrounded by a faint 

 external flat ring ; another has ansse, as if an annular nebulous 

 ring encompassed it and was foreshortened. Two annular nebulae 



