48 Mr. J. Lunt. On the Oi^igin of certain Unhnoum 



at once gave the unknown lines, which were thas proved to be un- 

 doubtedly due to silicon. 



This silicon spectrum was not accompanied by that of oxygen, thu« 

 proving that it could not be due to any dissociation of the silica of 

 the glass, and that in this case, the gaseous contents of the tube and 

 not the tube itself, furnished the lines under consideration. 



Sir Norman Lockyer's papers were then consulted for any reference 

 to the presence of silicon in stars, and it is necessary to refer in some 

 detail to his observations. It is evident that he has used similar 

 powerful disruptive discharges with vacuum tubes, and obtained partial 

 decomposition of the glass, for he says " The use of the spark -vvith 

 large jars in vacuum tubes results in the partial fusion of the glass, 

 and the appearance of lines which have been traced to silicium." 



Unfortunately he does not give the wave-lengths of the lines thus 

 traced to silicon, and from his statement alone, one would surmise 

 that the origin of the three lines was recognised by Lockyer. 



There is evidence, however, the same paper that he cannot have 

 traced the lines in question to silicon notwithstanding the above state- 

 ment, because, as previously pointed out, Sir Norman regards two of 

 the lines as belonging to gases yet undiscovered, and includes them in 

 a Table of Wave-Lengths of lines due to unknown gases. 



The other line he also includes as an unknown line in Bellatrix, and 

 Dr. W. J. S. Lockyer places this as a member of a probable rhythmic 

 series due to an unknown substance. 



It is a curious fact that Hartley and Adeney, and Eder and Valenta, 

 who alone give us any extended list of lines due to silicon, appear 

 not to have examined the spectrum of this element in the region of 

 the three lines here considered. Their published wave-lengths show 

 only lines in the extreme ultra-violet, and the majority of them are 

 quite outside the region which can be examined by the McClean Star 

 Spectroscope. 



Watts's ' Index of Spectra' (Appendix E, p. 21) records a line at 4566 

 (Salet), but no lines appear corresponding to 4552*79 and 4574'68. 



Sir Norman Lockyerf regards two lines at 4128*6 and 4131 '4 as 

 the most conspicuous enhanced lines of silicon, indeed these two lines 

 are the only silicon lines he labels Si in his published photographs. 

 Eder and Yalenta give 4131-5 and 4126*5 as the least refrangible on 

 their list, and although there is a rather excessive discrepancy in the 

 wave-lengths of one of the lines, they are probably the same pair of 

 lines. They are shown in Lockyer's photographs of the spectra of 

 a Cygni and Siriusj and also of a Cygni and Eigel.§ 



* ' Roy. Soc. Proc.,' toI. 62, 1897, p. G5. 

 t ' EoT. Soc. Proc, Tol. 61, 1897, p. 443. 

 X ' Eoy. Soc. Proc.,' vol. 65, p. 191. 

 § ' Phil. Tran3.,' A (1893), plate 2. 



