1878.J Analysis in connexion with the Spectrum of the Sun. 163 



stances as they exist in A would contain as many lines as would 

 the spectrum of the substances as they exist in D ; each line would in 



Fig. 2. 



A 

 / 

 2 



3. 



B 



a 



3 



c 



/ 



a 



3- 



D 



_ 



turn be basic in the whole series of furnaces instead of in one or two 

 only. 



Application of these General Considerations to Impurity Elimination. 



Now let us suppose that in the last diagram (Fig. 2) the four 

 furnaces represent the spectra of say, iron, broken up into different 

 finenesses by successive stages of heat. It is first of all abundantly 

 clear that the relative thicknesses of the iron lines observed will vary 

 according as the temperature resembles that of A, B, C, or D. The 

 positions in the spectra will be the same, but the intensities will vary ; 

 this is the point. The longest lines, represented in the diagram by 

 the thickest ones, will vary as we pass from one temperature to 

 another. It is on this ground that I have before stated that the 

 whole fabric of impurity elimination must fall to pieces on such an 

 hypothesis. Let us suppose, for instance, that manganese is a com- 

 pound of the form of iron represented in furnace B, with something 

 else ; and suppose again that the photograph of iron which I compare 

 with manganese represents the spectrum of the vapour at the tempe- 

 rature of the furnace D. To eliminate the impurity of iron in manganese, 

 as I have eliminated it, we begin the search by looking for the longest 

 and strongest lines shown in the photograph of iron, in the photograph 

 of manganese taken under the same conditions. I do not find these 

 lines. I say, therefore, that there is no impurity of iron in manganese, 

 but although the longest iron lines are not there, some of the fainter 

 basic ones are. This I hold to be the explanation of the apparent con- 

 fusion in which we are landed on the supposition that the elements 

 are elementary. 



