Clusters and Nebulce. 345 



point to a gaseous constitution. In the spectra of several 

 "planetary" nebulas,, as Herschel I. designated those of an 

 unusually equable light and well-defined outline, three bright 

 narrow transverse bands are found at some distance from each 

 other, and of very dissimilar brightness— the strongest of which 

 corresponds with the position of a band in the spectrum of 

 nitrogen gas, the faintest with one in that of hydrogen, while 

 the one intermediate in position and brightness marks some 

 hitherto unverified element. In this annular nebula, owing, as 

 it seems, to the feebleness of its light as compared with that 

 of several objects of the same class, the possible line of 

 nitrogen alone is distinct, and that of the unknown component 

 merely suspected. " The bright line," Mr. Huggins states, 

 " looks remarkable, since it consists of two bright clots corres- 

 ponding to sections of the ring", and between these there was 

 not darkness, but an excessively faint line joining them. This 

 observation makes it probable that the faint nebulous matter 

 occupying the central portion is similar in constitution to that 

 of the ring." 



This is an astounding announcement. The conclusions 

 arrived at by two different modes of investigation seem utterly 

 irreconcilable. It is difficult to question the result obtained 

 by such a man as Secchi, and confirmed so fully by Chacornac. 

 On the other hand, the admirably ingenious method of obser- 

 vation adopted by Huggins, and the delicate precision of the 

 observation itself, are above all suspicion; and we seem to 

 hang upon the horns of a strange dilemma. Either the deter- 

 minations of spectrum analysis are perplexed by an experiment 

 which exhibits solid materials under the guise which gaseous 

 ones alone have hitherto been considered to assume, or else, in 

 defiance of all analogy, the silver- dust of Secchi and the scintil- 

 lating points of Chacornac must be held not to be stars, at least 

 in the ordinary meaning of the word. Huggins, who, with 

 due caution, doubts the identity of the bright band with that 

 of nitrogen, on account of the absence of other lines of 

 nitrogen, which are bright enough to be visible under the 

 same circumstances, yet entertains no question as to the indica- 

 tions which have been presented to him. After enumerating 

 eight planetary nebulas which he has examined, including the 

 one now before us, he says it is obvious that they " can no 

 longer be regarded as aggregations of suns after the order to 

 which our own sun and the fixed stars belong. We have in 

 these objects to do no longer with a special modification only 

 of our own type of suns, but find ourselves in the presence of 

 objects possessing a distinct and peculiar plan of structure. 

 In place of an incandescent solid or liquid body transmitting 

 light of all refrangibilities through an atmosphere which inter- 



