200 



NATURE 



\ya7i. 2, 1879 



cated a paper to the Society on the spectrum of calcium, 

 to which I shall refer more expressly in the sequel. 



Differentiation of the Pheno?nena to be observed on the 

 Two Hypotheses 



When the reductions of the observations made on 

 metallic spectra, on the hypothesis that the elements 

 were really elementary, had landed me in the state of 

 utter confusion to which I have already referred, I at 

 once made up my mind to try the other hypothesis, and 

 therefore at once sought for a critical differentiation of the 

 phenomena on the two hypotheses. 



Obviously the first thing to be done was to inquire 

 whether one hypothesis would explain these short line 

 coincidences which remained after the reduction of all 

 the observations on the other. Calling for simplicity' sake 

 the short lines common to many spectra basic lines^ the 

 new hypothesis, to be of any value, should present us with 

 a state of things in which basic molecules representing 

 bases of the so-called elements should give us their lines, 

 varying in intensity from one condition to another, the 

 conditions representing various compoundings. 



Suppose A to contain B as an impurity and as an element, 

 what will be the difference in the spectroscopic result ? 



A in both cases will have a spectrum of its own ; 



B as an impurity will add its lines according to the 

 amount of impurity, as I have shown in previous papers. 



B as an element will add its lines according to the 

 amount of dissociation, as I have also shown. 



The difference in the phenomena, therefore, will 

 be that, with gradually increasing temperature, the 

 spectrum of A will jade, if it be a compound body, as it 

 will be increasingly dissociated, and it will not fade if it 

 be a simple one. 



Again, on the hypothesis that A is a compound body, 

 that is, one compounded of at least two similar or dis- 

 similar molecular groupings, then the longest lines at one 

 temperature will not be the longest at another, the whole 

 fabric of "impurity elimination," based upon the assumed 

 single molecular grouping, falls to pieces, and the origin 

 of the basic lines is at once evident. 



This may be rendered clearer by some general con- 

 siderations of another order. 



Ccnet'al Considerations 



Let us assume a series of furnaces A ... D, of which 

 A is the hottest. 



A] 



r 



2 

 3 



Bl 

 f 

 2. 

 3. 



CI 

 r 

 1 

 3 



\f'^''\^\-,: 



l-i' 'i!iliii!liiiiili!aiiil 



npiiTTTITTr 



li-^aii JII!liliillii!lllililililliii!liilill!il!l!l!i!iii!i!i: 



iili!;: 



mMi 



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Fig. 1.^ 



Let us further assume that in A there exists a substance a 

 by itself competent to form a compound body ^3 by union 

 with itself or with' something else when the temperature 

 is lowered. 



Then we may imagine a furnace B in which this com- 

 pound body exists alone. The spectrum of the compound /3 

 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. 



A lower temperature furnace C will provide us with 



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

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



a more compound substance y, and the same considera- 

 tions Mill hold good. 



Now if into the furnace A we throw some of this 

 doubly compounded body y we shall get at first an integra- 

 tion of the three spectra to which I have drawn atten- 

 tion ; the lines of y will first be thickest, then those of 

 ^, and finally a would exist alone, and the spectrum would 

 be reduced to one of the utmost simplicity. 



This is not the only conclusion to be drawn from these 

 considerations. Although we have by hypothesis 13, y, 

 and S all higher, that is, more compound forms of a, and 

 although the strong lines in the diagram 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 /3 will be seen in furnace 



C, and the strong lines of y will be seen in furnace D, al^ 

 as thin lines. Thus, although in C we have no line which 

 is not represented in D, the intensities 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 /3 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 /S, y, and & 

 into a is far below that stage, although higher than B. 



Fis. 3. 



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 merely in the relative thicknesses 

 of the lines. The spectrum of the substances as they exist 

 in A would contain as many lines as would the spectrun^ 

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

 turn be basic in the whole series of furnaces instead of 

 in one or two only. 



Application of these General Considerations to Impurity 

 Elitnitiation 



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 thick- 

 nesses 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 intensi- 

 ties will vary ; this is the point. The longest lines, rC' 

 prese7ited in the diagram by the thickest ones, xuill vary 

 as we pass from one temperatiire 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 man- 

 ganese is a compound 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 temperature 

 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 



