400 Sir Norman Lockyer, On the Order of Appearance of 



The wave-lengths of the lines discussed are shown at the bottom of 

 the map. 



ADDENDUM. 



The facts embodied in the map present to us the spectral changes 

 noted in stars of Groups III, IV, and V, of my classification,* and 

 are a result of a more general inquiry than those referred to in my 

 previous papers,! the origins of a very considerable number of stellar 

 lines having since then been traced to enhanced lines of metals and to 

 known gases. 



It will be seen that this more general inquiry entirely justifies the 

 prior statement^ that the metallic lines are thickest in stars increasing 

 their temperatures, and that the hydrogen lines are thickest in stars 

 decreasing their temperatures ; in other words, on the opposite arms 

 of the temperature curve. I have already stated a possible explana- 

 tion^ 



It will be observed that, so far, I have not been able to find stellar 

 spectra on the downward side corresponding to those of y Argus and 

 Orionis ; but it is more than probable that near the apex of the curve 

 only a small change will be observed ; their default, therefore, is of 

 less consequence than it might have been. 



The same remark applies to a Cygni and Sirius ; but here it is cer- 

 tain that the differences in the relative intensities of the gaseous and 

 enhanced lines will be considerable, judging from what happens above 

 and below the heat stages represented by them. 



The stars used in the discussion give us very definite results, 

 showing that the various chemical forms are introduced at six very 

 distinct heat levels. 



I next proceed to make some remarks upon the series of facts now 

 for the first time brought together; it must, however, be borne in 

 mind that all the chemical elements and all parts of the spectrum 

 have not yet been included in the survey. 



1. Hydrogen appears throughout both series of stars from top to 

 bottom. Proto-magnesium and proto-calcium follow suit very 

 nearly ; but the highest intensity of the former is reached at the 

 stage represented by a Cygni, and of the latter at the solar tem- 

 perature represented by a Tauri and Arcturus. 



2. With the above exceptions, all the chemical forms so far traced 

 are relatively short-lived. 



This is the first important differentiation. In the light of (1) we 



* ' Roy. Soc. Proc.,' vol. 43, p. 117 (1887). 



t ' Roy. Soc. Proc.,' vol. 44, p. 1 (1888) ; ' Koy. Soc. Proc.,' vol. 45, p. 380 

 (1889) ; ' Phil. Trans.,' A, vol. 184 (1893), p. 725. 

 t ' Roy. Soc. Proc./ vol. 61, p. 182. 

 ' Roy. Soc. Proc.,' vol. 61, p. 183. 



