1878.] Mr. J. N. Lockyer. Researches in Spectrum Analysis. 157 



Dielectric. 





JN earest value 



Of 



Ray for which fj. 

 is nearest. 



Double extra dense flint 



1 -7783 



1 -7460 



Band in extreme 

 violet in mag- 

 nesium spark 

 spectrum. 





1 '7474 



1 -6757 





1 -7343 



1-5113 





1 -7629 



1 -5920 







1 -8009 



1543 







1 -4119 



1 -422 



Bays of infinite 

 wave length. 





1 -6060 



2-115 





Bisulphide of carbon. . . . 



1 3456 



1-6114 





YJ. " Researches in Spectrum Analysis in connexion with the 

 Spectrum of the Sun. No. VII." By J. N. Lockyer, 

 F.R.S. Received December 11. 1878. Read December 12. 



Discussion of the Working Hypothesis that the so-called Elements are 

 Compound Bodies. 



Part I. 



It is known to many Fellows of the Society that I have for the last 

 four years been engaged upon the preparation of a map of the solar 

 spectrum on a large scale, the work including a comparison of the 

 Fraunhofer lines with those visible in the spectrum of the vapour of 

 each of the metallic elements in the electric arc. 



To give an idea of the thoroughness of the work, at all events in in- 

 tention, I may state that the complete spectrum of the sun, on the 

 scale of the working map, will be half a furlong long ; that to map the 

 metallic lines and purify the spectra in the manner which has already 

 been described to the Society, more than 100,000 observations have 

 been made and about 2,000 photographs taken. 



In some of these photographs we have vapours compared with the sun ; 

 in others vapours compared with each other ; and others again have been 

 taken to show which lines are long and which are short in the spectra. 



I may state by way of reminder that the process of purification con- 

 sisted in this : When, for instance, an impurity of Mn was searched 

 for in Fe, if the longest line of Mn was absent, the short lines must 

 also be absent on the hypothesis that the elements are elementary ; if 

 the longest line were present, then the impurity was traced down to 

 the shortest line present. 



