On the Chemistry of the Hottest Stars. 199 



In approaching this new part of the subject, it is necessary to 

 proceed with great caution, since the things observed are different. 

 The solar work has consisted in observing different parts of the sun, 

 the star work puts us in presence of the total effects both of radia- 

 tion and absorption in the case of each body observed. 



A Possible Objection. 



But in limine there is an objection to meet which may possibly be 

 put forward by those unfamiliar with these inquiries. 



It is that there is no relation whatever between the sun and stars, 

 that there is no evolution, and that the various spectral differences 

 are due simply to the fact that the relative percentage composition 

 varies from sun to star and from star to star, so that some stars may 

 be composed entirely of the cleveite gases, others of hydrogen, others 

 of calcium, others of iron, others of carbon, and so on. 



Those who hold these views and deny that an evolution is going 

 on have to explain the following facts : — 



1. While the number of chemical elements known at the present 

 time is about seventy-two, the number of well-marked groups of stars is 

 only seven, and this number includes the nebulae. 



2. It is not sufficient to suppose differences due to a variation of 

 the number of chemical elements present in different stars, as there 

 may also be any number of 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 seven. 



3. Each particular kind of star spectrum is always associated with 

 the same degree of stellar temperature as determined by other con- 

 siderations. With differences of chemical composition, different 

 spectra would occur with equal temperatures. 



4. The Sun, Capella, and 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 pro- 

 portions. The earlier and hotter stages of such stars could not 

 therefore have consisted of different mixtures. 



5. All the blood-red stars, which it is generally acknowledged are 

 near the point of extinction, have identical spectra. 



6. The facts in this paper already given show 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 

 different temperatures on the same molecules. 



Until the above facts are explained I must hold that the argu- 

 ment is complete that we do get the same elements represented by 



