546 



Sir N. Lockyer and Mr. F. E. Baxandall. [Jan. 4, 



"On the Stellar Line near X 4686." By Sir NORMAN LOCKYRII, 

 KC.B., LL.D., Sc.D., F.E.S., and F. E. BAXANDALL, A.E.C.Sc. 

 Received January 4, Read February 9, 1905. 



[PLATE 13.] 



In the publication of the results derived from a study of the 

 Kensington photographic spectra of the 1898 eclipse, it was stated* 

 that a fairly prominent line recorded near A 4686, for which no 

 terrestrial origin could be found, agreed closely in position with a 

 well-marked line of unknown origin in one of the Kensington photo- 

 graphs of the spectrum from a helium tube. In the helium photo- 

 graph the position has been recently found from careful measures 

 made on the lines 4120'97, 4388*10, 4713-25, and the line in question, 

 and subsequent use of Hartmann's formula. 



The resulting wave-length of the strange line was 4685-97. Similar 

 measurements were made on the eclipse photographs, the fiducial 

 lines used being 4508-5 (p Fe), 4584-0 (pFe), and 4713-25 (He). The 

 result gave 4685-90. 



The two calculated wave-lengths so nearly agree that it is very 

 probable the line is of identical origin in the two cases. The eclipse 

 line is, moreover, of the same nature as the helium eclipse lines, long 

 and sharply defined. It would therefore seem that the line is due 

 to a gas which is associated in some way with helium. The line, 

 however, only appears in one photograph of the helium spectrum, and 

 whether this is due to the particular sample of helium used, or to 

 some special condition of current which is conducive to the appearance 

 of the strange line, it is impossible to say. 



A line near the same position has been recorded by various 

 spectroscopists in different celestial spectra. The following table 

 -contains the available records of the line in question : 



* < Phil. Trans.,' A, vol. 197, p. 202. 



