Enhanced Lines in the Spectrum of a Gygni. 321 



unknown origin, one in the hottest stars, the other in stars of inter- 

 mediate temperature. 



After the discovery of a terrestrial source of helium by Professor 

 Ramsay, I showed in a series of seven notes communicated to the 

 Royal Society,* May September, 1895, that the cleveite gases, which 

 I obtained by the process of distillation, accounted to a very great 

 extent for the first set. 



In 1897 in a series of three communications to the Royal Society,! 

 I pointed out that some of the other set of unknown lines in the stars 

 of intermediate temperature, taking a Cygni as an example, were due 

 to the enhanced spark lines of iron and other metals, the arc lines 

 being almost entirely absent. 



During the last year, this research has been continued; and latterly, 

 by the kindness of Mr. Hugh Spottiswoode, the photographs of the 

 enhanced lines have been obtained by the use of the large induction 

 coil, formerly belonging to Dr. Spottiswoode, P..R.S. I am anxious to 

 express here my deep obligation to Mr. Hugh Spottiswoode for the 

 loan of such a magnificent addition to our instrumental aids. 



The spark obtained by means of the Spottiswoode coil, is so luminous 

 that higher dispersions than those formerly employed can be effectively 

 used, and in consequence of this, the detection of the enhanced lines 

 becomes more easy; their number therefore has been considerably 

 increased. 



The observations have already been mapped for the following 

 substances : Fe, Mg, Ca, Si, Sr, Va, Ti, Ni, Mn, Cr, Co, Cu. 



In the accompanying photograph, a comparison is shown between 

 the lines of a Cygni and the enhanced lines of the above substances 

 thrown together. The extraordinary number of coincidences is seen 

 at a glance. The facts are as follows : 



The number of lines measured in the spectrum of a Cygni at 



Kensington between A37 98'1 and A.486 1'6 is 307 



Of these the number which approximately coincides with the 



enhanced metallic lines so far observed is 120 



The number of lines (excluding the hydrogen series) in a Cygni 

 of intensity over 4 (the maximum being represented by 

 10) is 40 



Of this number, the coincidences with enhanced metallic lines 



with the dispersion employed amount to 38 



I shall deal in a subsequent communication, when the enquiry has 

 reached a further stage, with the details for each element. 



* 1st Note, 'Koy. Soc. Proc.,' vol. 58, p. 67; 2nd, ibid., vol. 58, p. 113; 3rd, 

 ibid., Yol. 58, p. 116 ; 4th, ibid., vol. 58, p. 192 ; 5th, ibid., vol. 58, p. 193 6th' 

 ibid., vol. 59, p. 4 ; 7th, ibid., vol. 59, p. 342. 



t 'Roy. Soc. Proc.,' vol. 60, p. 475; ibid., vo 1 . 61, p. 148 ; ibid., vol. 61, p. 441. 



