1878.] Analysis in connexion with the Spectrum of the Sun. 161 



Following out these views, I some time since communicated a paper 

 to the Society on the spectrum of calcium, to which I shall refer more 

 expressly in the sequel. 



Differentiation of the Phenomena 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's 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 im- 

 purity, as I have shown in previous papers. 



B as an element will add its lines according to the amount of disso- 

 ciation, as I have also shown. 



The difference in the phenomena, therefore, will be that, with 

 gradually -increasing temperature, the spectrum of A will fade, 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 dissimilar 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 considerations of 

 another order. 



General Considerations. 



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

 hottest. 



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. 



