122 INORGANIC EVOLUTION, [CHAP, 



the chief difference is in the inversion of the intensities of the hydrogen 

 and the metallic lines. 



Hence the facts are distinctly against the view of different chemical 

 parishes in space ; they also suggest that we are not justified in even 

 conceding possible variations in the percentage composition. On this 

 ground an infinite variety of spectra might be expected, but, as already 

 stated, the number of well-marked groups is ten. 



The Sun, Capella, arid Arcturus, and other cooling stars, enormously 

 separated in space, contain the same spectral lines with almost identical 

 intensities, so that not only do they contain the same " elements," but 

 they contain them in absolutely identical proportions. The earlier and 

 hotter stages of such stars could not therefore have consisted of different 

 mixtures. 



Again, all the blood-red stars, which it is generally acknowledged 

 are near the point of extinction, have practically identical spectra. 



Another strong argument against the objection now under discussion 

 is that each particular kind of star spectrum is always associated with the 

 same degree of stellar temperature as determined by other considera- 

 tions, chiefly the extension of the spectrum into the ultra-violet. With 

 differences of chemical composition, different spectra would occur with 

 equal temperatures. 



We are therefore justified in the conclusion that the differences 

 recorded in stellar spectra do not come from a different percentage 

 composition of the elements present, but arise from the action of dif- 

 ferent temperatures in the same molecules and until the above facts 

 are explained, I must hold that the argument is complete that we do 

 get the same elements represented by different spectral lines in different 

 stars when the apparent differences are such as to suggest the objection 

 to which I am now referring. It is not a question of the absence of 

 elements, but of the absence of certain molecular complexities of each ele- 

 ment, which separates the spectrum of the sun from those of the stars 

 of various orders. 



Having said so much regarding the objection generally, I must 

 now proceed to discuss the only piece of evidence which has been 

 brought forward in support of it, namely, the alleged localisation of 

 certain chemical groups of stars in particular parts of space, arising 

 from the fact that certain of the chemical elements are only to be 

 found in certain regions. This localisation is not held to be a quantita- 

 tive one merely, that is, depending upon varying proportions of elements, 

 but upon their absolute absence here and there. 



I propose to discuss this question in the following way. 



Since we can only deal with the masses of matter in space which 

 are visible, it is obvious that any inquiry mto the distribution of the 



