CHAPTER XVII. 



A STUDY OF THE PURIFIED SPECTRA. 



IN the year 1878, then, we had, as a result of some years* 

 work, the spectra of the metallic elements purified in the 

 manner indicated in the previous chapter, compared minutely 

 with the spectram of the sun over a limited region that near H 

 and more generally over a much more extended one. 



We were now, then, in a position to inquire, in a very 

 definite manner, into a question to which reference has already 

 been frequently made the coincidence of solar and terrestrial 

 spectra; and further, we could see whether the purification 

 which had been effected gave us in the case of each substance 

 a spectrum peculiar to that substance. Nor was this all. 

 There was reason to hope that the complete working out of 

 the long and short principle might get rid of some of the 

 difficulties referred to in previous chapters ; such, for instance, 

 as that connected with the reduction of the number of lines 

 seen in the case of each substance in the hotter regions of 

 the solar atmosphere. 



It will be seen that on all these points the more minute 

 inquiry now rendered possible landed us in hopeless con- 

 fusion, and the difficulties to which attention has already been 

 drawn seemed to become more impossible of explanation the 

 further we went, that is, if we applied to them the ideas then 

 generally received. 



