-60 INORGANIC EVOLUTION. [CHAP. 



As this new hydrogen series seems to bear the same relation to the 

 well-known one as the pro to-metallic lines bear to the metallic, I 

 call the gas which produces it proto-hydrogen for the sake of clearness. 



The new series of lines has been found in the spectra of , e, S, and 

 K Orionis photographed at Kensington in 1892. 



Professor Pickering himself has since found this system of lines in 

 other stars than Puppis, 29 Canis Majoris among them, and Mr. 

 McClean, in his admirable work on the brightest stars of the southern 

 hemisphere, has obtained photographs of the spectrum of 7 Argus, in 

 which the new series appears. 



From a discussion of these stars in relation to the others photo- 

 graphed, there can be little doubt that we are here face to face with 

 the very hottest stars so far known : and that the new series of hydro- 

 gen lines represents one among the last stages of chemical simplifica- 

 tion so far within our ken. 



We are, therefore, now in a better position to determine the rela- 

 tion of this new gas to other gases, both known and unknown, appear- 

 ing in stars of nearly equal temperature. 



Other New Lines. 



But even with our present knowledge of stellar spectra we find 

 that in relation to the hottest stars there are still some gaps in our 

 chemical knowledge ; not only is this so, but have we any right to 

 assume, taking into account the limitations of our means of observa- 

 tion and of the strict limitation of our observations to the relatively 

 small part of space nearest us, enormous though it is, that we are 

 as yet really in touch with the highest stellar temperatures 2 



Again, we cannot be certain that the small number of stars as yet 

 studied puts us in presence of the highest stellar temperatures. Those 

 stars which apparently are at the very apex of the temperature curve 

 are involved in unknown lines, and require a special study. 



Two typical unknown lines have wave-lengths at 4089*2 and 

 4649'2,* and besides these three other unknown lines occur in 7 Argus. 



As these most probably reveal still undiscovered gases, I include 

 them in the following table showing the limits of stellar temperature 

 to which the various known and unknown lines, probably of gaseous 

 origin, extend. 



Mr. McClean has stated that certain of the oxygen lines (amongst 

 which is the strong triplet at XX 407(H, 4072*4, and 4076-3) appear in 

 the spectrum of j3 Crucis and other stars of nearly equal temperature. 

 My own observations, so far as they have gone, tend to confirm this 



* Proc. Roy, Soc., vol. Ixii, p. 52. 



