198 Note on the Spectrum of the Nebula of Orion. 



the universe, altogether distinct and of another order from the 

 group of cosmical bodies to which our Sun and the fixed stars 

 belong ; "* and that : " 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 peculiar and distinct 

 plan of structure. "f I shall take a subsequent opportunity of showing 

 how untenable is the view he now communicates, that, although the 

 nebulae represent early evolutionary forms, they are at a high tem- 

 perature and that the constituents of the mass are arranged in the 

 order of their vapour densities. I refrain from discussing these points 

 on the present occasion ; but I may remark that if such a view were 

 true, and we farther accept the statements that, the nebula line was 

 seen in the comets of 1866-67 and that Nova Cygni probably exists as 

 a planetary nebula of small angular diameter, we are driven to the 

 conclusion that comets reduce their temperature as they approach the 

 Sun, and that "new stars" get hotter as their luminosity diminishes. 



"Note on the Spectrum of the Nebula of Orion." By J. NORMAN 

 LOCKYER, F.R.S. Received and read February 13, 1890. 



In a former communication I gave in detail observations made by 

 means of a siderostat, which seemed to put beyond all reasonable 

 doubt the question of the origin and true wave-length of the chief 

 nebula line. Although, as I stated in the communication referred to, 

 I regard this question as one of secondary importance, I have com- 

 menced another series of investigations with a view of eliminating 

 all possible instrumental errors. The new method has not been 

 completely carried out, bat a sufficient approximation to it has been 

 reached to render the results obtained of some interest. 



Using the siderostat, object-glass, and collimator as before de- 

 scribed, the method in question consists in using a vacuum tube, 

 giving the lines both of hydrogen and nitrogen in front of the slit of 

 the collimator. The tube made for this purpose was found to have 

 leaked when there was an opportunity of using it, so that the obser- 

 vations of hydrogen and nitrogen, in comparison with the nebula 

 lines, have not been made in the same field of view at the same time. 

 The hydrogen tube and an air spark with iron poles (iron poles 

 being chosen in order to check the position of the nebula line near 

 X 495) were, however, placed alternately in front of the slit of the 

 collimator, and this enabled the observations to be made with almost 

 equal accuracy. I give the following extract from the Observatory 



* 'Eoy. Soc. Proc.,' vol. 14, p. 42. 

 t ' Phil. Trans.,' 1864, p. 442. 



