March i6, 1899] 



NA TURE 



403 



THE CHEMISTRY OF THE STARS IN 

 RELATION TO TEMPERATURE} 

 •T^HE recent advances in our knowledge which have 

 -'■ come from the combination and interaction of solar, 

 stellar and laboratory research, carried on by the aid of 

 instruments of much greater power than those formerly 

 used, have given us a firm chemical hold on all the groups 

 of stars in my classification of them. These groups were 

 established by discussing sequences of lines before the 

 origin of the lines had been made out. A series of 

 hieroglyphics is now replaced by chemical facts ; and 

 we can now study the chemistry of the stars, as well as 

 their order in a system of classification. 



The first question which naturally arises is this : Do 

 the chemical elements make themselves visible indis- 

 criminately in all the celestial bodies, so that practically, 

 from a chemical point of view, the bodies appear to us of 

 similar chemical constitution ? This is not so. 



From the spectra of those stars which resemble the 

 sun, in that they consist of an interior nucleus surrounded 

 by an atmosphere which absorbs the light of the nucleus, 

 and which therefore we study by means of this absorp- 

 tion, it is to be gathered that the atmospheres of some 

 stars are chiefly gaseous, i.e. consisting of elements we 

 recognise as gases here, of others chiefly metallic, of 

 others again mainly composed of carbon or compounds 

 of carbon. 



Here then we have spectroscopically revealed the fact 

 diat there is considerable variation in the chemical 

 constituents which visibly build up the stellar atmo- 

 spheres. 



This, though a general, is still an isolated statement, 

 ban we connect it with another ? 



: By means of one of the first principles of spectrum 

 analysis we know that the hotter a thing is, the light of 

 ivhich produces a continuous spectrum, the further does 

 ^he spectrum stretch into the violet and ultra-violet. 



Hence the hotter a star is, the further does its com- 

 plete or continuous spectrum lengthen out towards the 

 ultra-violet, and, fa^/i';7>/(r>7y'/cj', the less is it absorbed 

 by cooler vapours in its atmosphere. 

 I Now to deal with three of the main groups of stars, we 

 find the following very general result : — 



Gaseous stars ... ... Longest spectrum. 



Metallic stars ... ... Medium spectrum, 



I Carbon stars ... ... Shortest spectrum. 



j We have now associated two different series of pheno- 

 mena, and we are entitled' to make the following general 

 Itatement : — 



Gaseous stars 

 Metallic stars 

 Carbon stars 



Highest temperature. 

 Medium temperature. 

 Lowest temperature. 



( Hence the differences in apparent chemical constitu- 



Iions are associated with differences of temperature. 

 This, then, is the result of our first inquiry into the 

 Existence of the various chemical elements in the atmo- 

 Ipheres of stars generally. We get a great diversity, 

 ^nd we know that this diversity accompanies changes of 

 emperature. We also find that the sun, which we 

 Tidependently know to be a cooling star, and Arcturus, 

 ire identical chemically. 



I I ne.xt pass from the general to the particular, and 

 Hve the detailed results recently obtained in the case of 

 jitars as hot or hotter than Arcturus — taking Arcturus to 

 lepresent the solar temperature. 



( In a paper on the " Chemistry of the Hottest Stars," ^ 



II 1S97, I slated the results so far arrived at concerning 

 he order in which certain spectral lines appeared, and 

 thers disappeared, in stars arranged in a series of 



iscending temperatures. 



V- This article embodies a paper read at the Royal Society on Thursday, 



ebruary 23. 



rl2 P...,. r„„ c,- vol. Ixi. p. 148. 



Roy. Soc. 



NO. 1533, 



VOL. 59] 



Since that paper was written many important advances 

 have been made, among them I may mention the 

 following : 



Pro/o-nictais. 



With regard to the metals, the recent work on the 

 enhanced lines in the spectrum of metals, a Cygni ' and 

 the sun's chromosphere enables us to deal with the lines 

 observed at the highest temperature in the spectra of the 

 following substances : magnesium, calcium, iron, man- 

 ganese, nickel, chromium, titanium, copper, vanadium, 

 strontium, silicium. 



The accompanying untouched reproductions of photo- 

 graphs will show the wonderful similarity which exists 

 between these three spectra. 



As we have to deal both with the arc and spark lines 

 of these substances, for the sake of clearness I call the 

 latter '■'■ pro/o-metaliic" lines, and consider the substances 

 which produce them, obtamed at the highest available 

 laboratory temperatures, " proto-metals," that is, a finer 

 form of the metal than that which produces the arc lines, 

 corresponding to the " meta-elements " imagined by 

 Crookes. 



The temperature ranges of the enhanced lines of these 

 metals have been irrvestigated in various stars with the 

 following results : — 



I pointed out in the note referred to that the enhanced 

 lines of the above substances seemed to account for 

 almost all of the more marked lines in a Cygni. It is 

 on this ground that I have investigated their behaviour 

 in other stars before waiting for the results of the com- 

 plete inquiry. Another reason has been that, although 

 in addition to the enhanced lines of the metals shown 

 in the foregoing table, those of barium, cadmium, 

 molybdenum, lanthanum, antimony, lead, palladium, 

 tantalum, erbium and yttrium, tungsten, cerium, uranium, 

 cobalt and bismuth have already been investigated with 

 lower dispersion, and a spark obtained with the use of a 

 much less jar capacity, so far I have no certainty that 

 any of these substances exist in the reversing layers of 

 stars of intermediate temperature. 



The temperature ranges of the arc lines of some of 

 the metals have also been investigated, and the results 

 are shown in the following table :- - 



Iron 



Calcium ... 

 Manganese 



Range of temperature 

 (upward series). 



o Tauri to a Cygni 



a Tauri to o Ursie Min. 



o Tauri to a Ursae Min. 



Range of temperature (do 



a Canis Majoris to Arcturus 

 o (ianis Majoris to Arcturus 

 a Canis Majoris to Arcturus 



So much, then, for the metals. I now turn to the gases. 



Proto-hydrogen . 

 Some little time ago Prof. Pickering, of Harvard 

 Observatory, found on e.xamining the spectra of the 

 1 Natcre, February 9 (p. 342). 



