of the Great Nebula in the Sword-handle of Orion. 321 



lines only. The whole of this Great Nebula, as far as it lies within 

 the power of my instrument, emits light which is identical in its 

 characters ; the light from one part differs from the light of another 

 in intensity alone. 



The clustering stars of which, according to Lord Rosse and Pro- 

 fessor Bond, the brighter portions of this nebula consist, cannot be 

 supposed to be invisible in the spectrum apparatus because of their 

 faintness, an opinion which is probably correct of the minute and 

 widely separated stars seen in the Dumb-bell nebula, and to which 

 reference was made in my former paper. The evidence afforded 

 by the largest telescopes appears to be that the brighter parts of the 

 nebula in Orion consist of a "mass of stars;" the whole, or the 

 greater part of the light from this part of the nebula, must there- 

 fore be regarded as the united radiation of these numerous stellar 

 points. Now it is this light which, when analyzed by the prism, 

 reveals to us its gaseous source, and the bright lines indicative of 

 gaseity are free from any trace of a continuous spectrum, such as 

 that exhibited by all the brighter stars which we have examined. 



The conclusion is obvious, that the detection in a nebula of minute 

 closely associated points of light, which has hitherto been con- 

 sidered as a certain indication of a stellar constitution, can no longer 

 be accepted as a trustworthy proof that the object consists of 

 true stars. These luminous points, in some nebulae at least, must 

 be regarded as themselves gaseous bodies, denser portions, probably, 

 of the great nebulous mass, since they exhibit a constitution which 

 is identical with the fainter and outlying parts which have not 

 been resolved. These nebulse are shown by the prism to be enor- 

 mous gaseous systems ; and the conjecture appears probable that their 

 apparent permanence of general form is maintained by the continual 

 motions of these denser portions which the telescope reveals as lucid 

 points. 



The opinions which have been entertained of the enormous distances 

 of the nebulse, since these have been founded upon the supposed 

 extent of remoteness at which stars of considerable brightness would 

 cease to be separately visible in our telescope, must now be given up 

 in reference at least to those of the nebulae the matter of which has 

 been established to be gaseous. 



It is much to be desired that proper motion should be sought 

 for in those of the nebulae which are suitable for this purpose ; 

 indications of parallax might possibly be detected in some, if any 

 nebulse could be found that would admit of this observation. 



If this view of the greater nearness to us of the gaseous nebulse 

 be accepted, the magnitudes of the separate luminous masses which 

 the telescope reveals as minute points, and the actual intervals 

 existing between them, would be far less enormous than we should 

 have to suppose them to be on the ordinary hypothesis. 



It is worthy of consideration that all the nebulse which present a 

 gaseous spectrum exhibit the same three bright lines ; in one case 

 only, 18 H.IV., was a fourth line seen. If we suppose the gaseous 

 substance of these objects to represent the "nebulous fluid" out 



