162 Mr. J. N. Lockyer, Researches in Spectrum [Dec. 12, 



Then we may imagine a furnace B in which this compound body 

 exists alone. The spectrum of the compound ft would be the only one 

 visible in B, as the spectrum of the assumed elementary body a would- 

 be the only one visible in A. 



Fig. 1 * 



A lower temperature furnace C will provide us with a more com- 

 pound substance 7, and the same considerations will hold good. 



Now if into the furnace A we throw some of this doubly-com- 

 pounded body 7, we shall get at first an integration of the three spectra 

 to which I have drawn attention ; the lines of 7 will first be thickest, 

 then those of (3 ; finally a will exist alone, and the spectrum will be 

 reduced to one of the utmost simplicity. 



This is not the only conclusion to be drawn from these considera- 

 tions. Although we have by hypothesis (B, 7, and S all higher, that is, 

 more compound forms of a, and although the strong lines in the dia- 

 gram may represent the true spectra of these substances in the 

 furnaces B, C, and D, respectively, yet, in consequence of incomplete 

 dissociation, the strong lines of (B will be seen in furnace C, and the 

 strong lines of 7 will be seen in furnace D, all as thin lines. Thus, 

 although in C we have no line which is not represented in D, the in- 

 tensities of the lines in C and D are entirely changed. 



In short, the line of a strong in A is basic in B, C, and D, the lines 

 of (B strong in B are basic in C and D, and so on. 



I have prepared another diagram which represents the facts on the 

 supposition that the furnace A, instead of having a temperature 

 sufficient to dissociate (3, 7, and 8 into a is far below that stage, 

 although higher than B. 



It will be seen from this diagram that then the only difference in 

 the spectra of the bodies existing in the four furnaces would consist 

 in the relative thicknesses of the lines. The spectrum of the sub- 



* The figures between the hypothetical spectra point to the gradual change as the 

 spectrum is observed near the temperature of each of the furnaces. 



