206 LECTURE ON THE EESULTS OF SPECTEUM ANALYSIS 



It is remarkable tliat tbe easily resolved cluster in Hercules has a spectrum 

 precisely similar. The prismatic connection of this cluster with the nebula in 

 Andromeda is confirmed by telescopic observation. Lord Rosse has discovered 

 in this cluster dark streaks or lines similar to those which are seen in the 

 nebula in Andromeda. 



In connection with these observations, it was of great interest to ascertain 

 whether the broad classification afforded by the prism of the nebulae and clus- 

 ters would correspond with the indications of resolvability furnished by the tele- 

 scope. Would it be found that all the unresolved nebulse are gaseous, and that 

 those which give a continuous spectrum are clusters of star si 



Lord Oxmantown has examined all the observations of the sixty nebulse and 

 clusters in my list, which have been made with the great reflectiDg telescope 

 erected by his father the Earl of Eosse. 



The results are given in this diagram : 



Continuous Gaseous 



Spectrum. Spectrum. 



Clusters 10 



Resolved, or Resolved ? 5 



Resolvable, or resolvable ? 10 '6 



Blue or green, no resolvability, no resolvability seen \ c ^ 



31 15 



Not observed by Lord Rosse 10 4 



41 19 



t- 



Considering the great difficulty of successful telescopic observation of these 

 objects the correspondence between the results of prismatic and telescopic ob- 

 servation may be regarded as close and suggestive. 



Half of tbe nebulse which give a continuous spectrum have been resolved, 

 and about one-third more are probably resolvable; while of the gaseous nebulae 

 none have been certainly resolved, according to Lord Rosse. 



The inquiry now presents itself upon us, what superstructure of interpreta- 

 tion have we a right to raise upon the new facts with which the prism has fur- 

 nished us % 



Is the existence of the gaseous nebulse an evidence of the reality of that pri- 

 mordial nebulous matter required by the theories of Sir William Herschel and 

 Laplace. 



Again, if we do not accept the view that these nebulse are composed of por- 

 tions of the original elementary matter out of which suns and planets have been 

 elaborated, what is the cosmical rank and relation which we ought to assign to 

 them? 



As aids to ii future determination of these great questions I will refer in a few 

 words to some other observations. 



COMETS. 



There are objects in the heavens which occasionally, and under some condi- 

 tions, resemble closely some of the nebulse. In some positions in their orbits 

 some of the comets appear as round vaporous masses, and, except by their mo- 

 tion, cannot be distinguished from nebulse. Does this occasional general resem- 

 blance indicate a similarity of nature % If such be the case, if the material of 

 the comets is similar to that of the nebulse, then the study of the wonderful 

 changes which comets undergo in the neighborhood of the sun may furnish use- 

 ful information for a more correct interpretation of the structure and condition 



