

SPIRAL NEBULA'. 



of the masses of stars which could assume such forms would be 

 vain. The number of instances as yet detected, in which this 

 form prevails, is not great ; but it is sufficient to prove that the 

 phenomenon, whatever be its cause, is the result of the operation 

 of some general law. It is pretty certain, that when the same 

 powerful instruments which have rendered these forms visible in 

 objects which had already been so long under the scrutiny of the 

 most eminent observers of the last hundred years, including Sir 

 W. and Sir J. Herschel, aided by the vast telescopic powers at 

 their disposition, without raising even a suspicion of their real 

 form and structure, have been applied to other nebula;, other cases 

 of the same phenomenon willbe brought to light. In this point of 

 view it is much to be regretted, that the telescopes of Lord Rosse 

 cannot have the great advantage of being used under skies- 

 more favourable to stellar researches, since the discovery of such 

 forms as these not only requires instruments of such power as Lord 

 Rosse alone possesses at present, but also the most favourable 

 atmospheric conditions. 



In connection with this class of objects, and indeed with the 

 nebulae generally, one of the most remarkable is situate (n A 13 b 

 33 m NP D 41 56'); as shown in fig. 31, it was observed and drawn 

 by Sir John Herschel. " This is," says that eminent astronomer, 

 41 in many respects, one of the most remarkable and interesting of 

 its class, and has been submitted to elaborate examination by all 

 the eminent observers." The distance of the centre of the small 

 nebula from that of the large one, is given by Messier, as 4' 35", 

 which may serve as a modulus for its other dimensions. It was 

 described by Sir "W. Herschel as a bright round nebula, surrounded 

 by a halo or glory, and attended by a companion. Sir J. Herschel 

 observed this object, and represented it as in the figure. He 

 noticed the partial division of the ring, as if it were split, as its 

 most remarkable and interesting feature, and inferred that, sup- 

 posing it to consist of stars, the appearance it would present to an 

 observer, placed on a planet attached to one of them excentrically 

 situate towards the north preceding quarter of the central mass, 

 would be exactly similar to that of the milky way as seen from 

 the earth, traversing in a manner precisely similar the firmament 

 of large stars, into which the central cluster would be seen pro- 

 jected, and (owing to its greater distance) appearing like it to 

 consist of stars much smaller than those in other parts of the 

 heavens. " Can it be," asks Sir J. Herschel, " that we have here 

 a brother system, bearing a real physical resemblance and strong 

 analogy of structure to our own ? " Sir J. Herschel further argues, 

 that all idea of symmetry caused by rotation must be relinquished, 

 considering that the elliptical form of the innet subdivided portion 



81 



