XIIL] INTENSITIES OF LINES. 173 



observers by the success which had attended the labours of 

 Rutherfurd, Miller and Huggins, Secchi, and other observers in 

 recording the spectra of stars. 



This most interesting inquiry naturally enabled us to know 

 whether the stars gave spectra quite like the sun, and if it 

 happened that they did not give spectra like the sun or each 

 other, then such a result would not only define the points 

 of difference but would be sure to give us some excellent 

 working suggestions. 



How striking the differences actually were, not only between 

 sun and star, but between star and star, will be shown in the 

 sequel. 



4. Divergences between the Lines in the Spectra of Vapours 

 and the Fraunhofer Lines. 



Kirchhoff in his memorable paper of 1861, which may justly be 

 regarded as the basis of all subsequent work, was careful to 

 state that the sixty iron lines in the sun to which he referred, 1 

 agreed, "as a rule" in intensity with those observed in the 

 electric spark. Those who have given an account of his work 

 have not always been so cautious. Indeed, I find my friend 

 Professor Roscoe 2 running beyond the record in the following 

 sentence : 



" In order to map and determine the positions of the bright lines 

 found in the electric spectra of the various metals, Kirchhoff, as I 

 have already stated, employed the dark lines in the solar spectrum 

 as his guides. Judge of his astonishment when he observed that 

 dark solar lines occur in positions connected with those of all the 

 bright iron lines ! Exactly as the sodium lines were identical with 

 Fraunhofer's lines, so for each of the iron lines, of which Kirchhoff 

 and Angstrom have mapped no less than 460, a dark solar line was 

 seen to correspond. Not only had each line its dark representative 



1 Researches on the Solar Spectrum and the Spectra of the Chemical Elements, 

 Roscoe's translation, part i. p. 19. 



2 Spectrum Analysis, 3rd edit. p. 240. 



