XX.] STELLAR EVIDENCE REGARDING INORGANlO EVOLUTION. 159 



was out of the question ; but, thanks to the recent advances, we can 

 deal with this inorganic evolution from a chemical stand-point, and 

 what we have now to do is to consider tlie result of this inquiry. 



Chapters VI and VII give the evidence on which the statement 

 can now be firmly made, that in the hottest stars we are brought in 

 presence of a very small number of chemical elements. As we" come 

 down from the hottest stars to the cooler ones the number of spectral 

 lines increases, and with the number of lines the number of chemical 

 elements. I will only refer to the known substances it looks as if at 

 present we have still many unknowns to battle with. In the hottest 

 stars of all, we deal with a form of hydrogen which we do not know 

 anything about here (but which we suppose to be due to the presence 

 of a very high temperature), hydrogen as we know it, the cleveite 

 gases-, and magnesium arid calcium in forms which are difficult to get 

 here ; we think we get them by using the highest temperatures avail- 

 able in our laboratories. In the stars of the next lower temperature 

 we find the existence of these substances continued in addition to the 

 introduction of oxygen, nitrogen, and carbon. In the next cooler 

 stars we find silicium added ; in the next we note the forms of iron, 

 titanium, copper, and manganese, which we can produce at the very 

 highest temperatures available in our laboratories ; and it is only when 

 we come to stars much cooler that we find the ordinary indications of 

 iron, calcium, and manganese and other metals. All these, therefore, 

 seem to be forms produced by the running down of temperature. As 

 certain new forms are introduced at each stage, so certain old forms 

 disappear. 



The salient features of the organic record are thus exactly reproduced, 

 to such an extent indeed that the most convenient way to present the 

 results was to define the various star-stages by means of the chemical 

 forms which they reveal to us in exactly the same way as the geologists 

 have done in regard to organic forms ; so that we may treat these 

 stellar strata, so to speak, as the equivalent of the geological strata. 



From the hottest to the coldest stars I have found ten groups so 

 -distinct from each other chemically that they require to be dealt with 

 separately as completely as do the Cambrian and the Silurian forma- 

 tions. Imitating the geologist still further, I have given names ending 

 in ian- to these groups or genera beginning with the hottest, that is the 

 oldest dealing with the running down of temperature : These are 

 Argonian, Alnitamian, Achernian, Algolian, Markabian [a " break in 

 strata "], Sirian, Procyonian, Arcturian (solar), Piscian. 



I have also defined the chemical nature of these stellar strata as 

 the geologist defines the nature of any of his various beds ; we can say, 

 for instance, that the Achernian stars contain chiefly h5 T drogen, 



