XX.] STELLAR EVIDENCE REGARDING INORGANIC EVOLUTION. 161 



more important on account of what it indicates as to the presence of 

 the chemical elements in the stars than it is for what it omits. 



There are a great many reasons why some of the substances which 

 may exist in these stars should not make their appearance. I wish to 

 enlarge upon the fact that, seeing the very small range of our photo- 

 graphs of stellar spectra, seeing also that it doesjnot at all follow that 

 the crucial lines of the various chemical substances will reveal them- 

 selves in that particular part of the spectrum which we can photo- 

 graph, the negative evidence is of very much less importance than 

 the positive evidence. I think it is possible, for instance, that^we must 

 add lithium to the substances which we find in the table on pages 70 

 and 71, we must certainly include sodium and also aluminium, and 

 chlorine possibly, but about sulphur at present I have no certain 

 knowledge. At all events, we can with the greatest^confidence point 

 out the remarkable absence of substances of high atomic weight, and 

 the extraordinary thing that the metals magnesium, calcium, sodium 

 and silicium undoubtedly began their existence in the hottest stars long 

 before, apparently, there is any obvious trace of many of the other 

 metals which a chemist would certainly have been looking out for. 



