1865.] of the Great Nebula in the Sword-handle of Orion. 41 



fifth star y' and the sixth a' are seen in the telescope, but the spectra of 

 these are too faint for observation. 



The positions in the spectra of a, ft, y, S Trapezii, which correspond to 

 the positions in the spectrum of the three bright lines of the nebula, were 

 carefully examined, but in no one of them were dark lines of absorption 

 detected. 



The part of the continuous spectra of the stars a, /3, y, near the position 

 in the spectrum of the brightest of the bright lines of the nebula, appeared 

 on a simultaneous comparison to be more brilliant than the line of the 

 nebula, but in the case of y the difference in brightness was not great. The 

 corresponding part of 2 was perhaps fainter. In consequence of this small 

 difference of brilliancy, the bright lines of the adjacent nebula appeared to 

 cross the continuous spectra of y and c Trapezii. 



Other portions of the nebula were then brought successively upon the 

 slit ; but throughout the whole of those portions of the nebula which are 

 sufficiently bright for this method of observation the spectrum remained 

 unchanged, and consisted of the three bright 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 Professor 

 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 

 therefore be regarded as the united radiation cf 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 considered 

 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 nebulse 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 nebulae are 

 shown by the prism to be enormous gaseous systems ; and the conjecture 

 appears probable that their apparent permanence of general form is main- 

 tained by the continual motions of these- denser portions which the tele- 

 scope reveals as lucid points. 



The opinions which have been entertained of t lie enormous distances of the 



