398 Sir Norman Lockyer. On the Order of Appearance of 



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

 which is the strong triplet at XX 4070-1, 4072-4, and 4076-3) appear in 

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

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

 view, but other photographs and more laboratory work are needed to 

 explain certain changes of intensity which have been observed. The 

 lines attributed by Mr. McClean to oxygen have been noted between 

 a Crucis and Orionis in the upward series, and in stars at about the 

 a Eridani stage of temperature in the downward series. 



6. There is evidence that the strongest lines of nitrogen at X 3995*2 

 and X 46 30 '9 make their appearance in stars at about the temperature 

 of a Crucis. These lines appear from Eigel to f Orionis in the upward 

 series, and are present in stars at the a Eridani stage in the downward. 



7. I pointed out many years ago* that at high temperatures the 

 flutings of carbon in the violet are replaced by a line at X 42 6 7 -5. 

 There is a line at this wave-length in the spectra of stars ranging in 

 temperature from that of Rigel to f Orionis on the up side, and from 

 a Eridani to ft Persei on the down side, of the temperature curve. 



There is no known line of gases or metals to which this line can be 

 assigned. It is probable therefore that carbon exists in stars of the 

 same temperature as that at which oxygen and nitrogen have been 

 traced. 



8. Two lines in the spectrum of silicium (X 4128-5 and X 4131-5) 

 have been traced in stars between the temperatures of a Ursse Min. 

 and a Crucis in the upward series and between those of a Eridani and 

 Procyon in the downward. 



The accompanying map shows the facts relating to stars as hot as, 

 or hotter than, the sun, as we know them at present. 



Description of Map. 



The map is arranged on the following plan : The temperature of 

 the sun and Arcturus forms the lowest stage. The upper limit is 

 defined by y Argus, the hottest star so far known. On the left the 

 stars named are those of increasing temperature ; on the right those of 

 decreasing temperature. Those on the same horizon represent equal 

 mean temperatures so far as the cleveite gas and enhanced lines help 

 us to determine them. The blank spaces indicate that so far no star 

 has been photographed in the spectrum of which the enhanced lines 

 exactly match those on the opposite side. 



The names of the various chemical substances included in the dis- 

 cussion are given at the top. I have retained the prefix " proto-" to 

 that condition of each metallic vapour which gives us the enhanced 

 lines alone, and I have added it to that form of hydrogen seen only in 

 the hottest stars. 



* ' Eoy. Soc. Proc.,' vol. 30, p. 461. 



