64 INORGANIC EVOLUTION. [CHAP. 



The Temperature Ranges. 



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. 



The facts indicate individual peculiarities ; some chemical forms 

 appear to be longer lived than others, and, further, the important 

 spectral changes in the case of different substances do not occur at 

 the same temperature. 



(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 repre- 

 sented by a Cygni, and of the latter at the solar temperature represented 

 by a Tauri and Arc turns. 



(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 

 are justified in assuming that tho substances in (2) would be visible in 

 the stellar reversing layers if they were there. 



(3) In the stars of higher temperatures we deal generally with 

 gases. Below the stages represented by /3 Orionis and y Lyra? we 

 deal with proto-metals and metals, hydrogen being the only exception. 



(4) The proto-metals make their appearance at about the same heat- 

 level at which the gases (with carbon), always excepting hydrogen, 

 begin to die out. 



This is the second important differentiation. It is interesting to 

 notice the distinct difference of behaviour of carbon and silicium in the 

 descending series ; the former goes through the same stages as oxygen 

 and nitrogen, the latter behaves like the proto-metals. 



(5) With the exception of iron the metals, as contra-distinguished 

 from the proto-metals, only make their appearance in stars at and 

 below the heat level of Sirius. 



This is the third important differentiation. It is accompanied with 

 a notable diminution of hydrogen and proto-magnesium, and with an 

 increase of proto-calcium ; indeed, the latter seems generally to vary 

 inversely with the hydrogen. 



The question arises whether the order of visibility at reduced tem- 

 peratures now indicated does not explain the absence of proto-hydro- 

 gen, oxygen, and nitrogen from the spectra of the sun and nebulae ; the 

 metals present in, and the absence of quartz from, meteorites, and the 

 similarity of the gaseous products obtained from meteorites and metals, 

 native and other, in vacuo at high temperatures. 



