On the Chief Line in the Spectrum of the Nebula. 167 



" On the Chief Line in the Spectrum of the Nebula." By 

 J. NORMAN LOCKYER, F.R.S. Received December 9, 1889, 

 Read January 16, 1890. Revised May, 1890. 



I. Introductory. 

 1 T. The accuracy attainable in these inquiries. 



III. Wave-length of the chief nebula line. 



A. Historical notice. 



B. Laboratory observations with high dispersion in connexion with the 



chief nebula line. 



C. Observations by a new method. 



IV. Fluted character of the chief nebula line. 

 V. Conclusion. 



I. INTRODUCTORY. 



In 1887, reasoning from the spectral phenomena in stars of Vogel's 

 Class Ilia, which my researches proved to be due to the mixture of 

 bright flutings of carbon and dark flutings of manganese and other 

 substances, I came to the conclusion that these stars could not be 

 stars in the ordinary sense but swarms of bodies separated from each 

 other. 



I next showed, reasoning again from the spectral phenomena, that 

 these bodies were in all probability meteorites or particles of meteoritic 

 dust. 



A discussion of the origin of such stars as these next suggested 

 that it must be sought for in the nebulae. Meteoritic dust was then 

 experimented upon and two lines of unknown origin in the spectrum 

 of this dnst were found to be roughly in the same position as two 

 lines of unknown origin in the nebula spectrum. 



In my first communication to the Royal Society on this subject I 

 stated that the conclusions were "given with great reserve," and I 

 was careful to point oat that I had limited myself to small dispersion 

 (1 prism of 60), because it was imperative that all the observations 

 should be strictly comparable ; those of very faint glows visible with 

 difficulty and those of a bright electric arc, to speak only of laboratory 

 work ; and 1 also added that there was an additional reason for this 

 in the difficulty of obtaining astronomical observations with large 

 dispersions in the case of very dim celestial objects. 



Seeing, therefore, that I dealt only, of set purpose, with small 

 dispersion, I limited myself to a " short title " of three figures in my 

 references to the lines. 



Bat, although I did not employ great dispersion in the first in- 

 stance, I fully understood that this must be done eventually, so I at 



YOL. XLVIII. N 



