Chemical Substances at different Stellar Temperatures. 397 



certainty that any of these substances exist in the reversing layers of 

 stars of intermediate temperature. 



2. The temperature ranges of the arc lines of some of the metals 

 have also been investigated, and the results are shown in the following 

 table : 



3. The new series of lines discovered by Professor Pickering, and 

 described by him as representing a new form of hydrogen,* has been 

 found in the spectra of f, c, 8, and K Orionis photographed at Kensing- 

 ton in 1892, and Mr. McClean has traced the lines in y Argus. 



We are therefore now in a better position to determine the relation 

 of this new gas to other gases, both known and unknown, appearing in 

 stars of nearly equal temperature. 



4. In addition to the unknown lines at XX 40S9'2 and 4649'2, referred 

 to in my last communication on this subject,! 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 

 origins, extend. 



* ' Astrophys. Journ.,' vol. 5, p. 92 (1897). 

 f ' Roy. Soc. Proc.,' vol. 62, p. 52. 



