84 Mr. J. N. Lockyer on Spectrum- Analysis. [Dec. 12, 



It is pointed out that the phenomena observed are of the same nature as 

 those already described by Stokes, W, A. Miller, Eobinson, and Thalen,but 

 that the application o£ this method enables them to be better studied, the 

 metallic spectra being clearly separated from that of the gaseous medium 

 through, which the spark passes. Photographs of the spark, taken in air 

 between zinc and cadmium and zinc and tin, accompany the paper, show- 

 ing that when spectra of the vapours given off by electrodes are studied 

 in this manner, the vapours close to the electrode give Hues which dis- 

 appear from the spectrum of the vapour at a greater distance from 

 the electrode, so that there appear to be long and short lines in the 

 spectrum. 



The following elements have been mapped on this method : — Na, 

 Li, Mg, Al, Mn, Co, Ni, Zn, Sr, Cd, Sn,'Sb, Ba, and Pb, the lines 

 being laid down from Thalen's maps, and the various characters and 

 lengths of the lines shown. 



In some cases the spectra of the metals, enclosed in tubes and subjected 

 to a continually decreasing pressure, have been observed. In all these 

 experiments the lines gradually disappear as the pressure is reduced, the 

 shortest lines disappearing first, and the longest lines remaining longest 

 visible. 



Since it appeared that the purest and densest vapour alone gave the 

 greatest number of lines, it became of interest to examine the spectra of 

 compounds consisting of a metal combined with a non-metallic element. 

 Experiments with chlorides are recorded. It was found in all cases that 

 the difference between the spectrum of the chloride and the spectrum of 

 the metal was that under the same spark-conditions all the short lines 

 were obliterated. Changing the spark-conditions, the final result was that 

 only the very longest lines in the spectrum of the metallic vapour re- 

 mained. It was observed that in the case of elements with low atomic 

 weights, combined with one equivalent of chlorine, the numbers of lines 

 which remain in the chloride is large, 60 per cent., e. g., in the case of Li, 

 and 40 per cent, in the case of Na ; while in the case of elements with 

 greater atomic weights, combined with two equivalents of chlorine, a much 

 smaller number of lines remain — 8 per cent, in the case of barium, and 

 3 per cent, in the case of Pb. 



The application of these observations to the solar spectrum, to elucidate 

 which they were undertaken, is then given. 



It is well known that all the known lines of the metallic elements on 

 the solar atmosphere are not reversed. Mr. Lockyer states what Kirch- 

 hoff and Angstrom have written on this subject, and what substances, 

 according to each, exist in the solar atmosphere. He next announces the 

 discovery that, with no exception whatever, the lines whichjtre reversed are 

 the longest lines. With this additional key he does not hesitate to add, on 

 the strength of a small number of lines reversed, zinc and aluminium (and 

 possibly strontium) to the last list of solar elements given by Thalen, who 



