VI.] 



CHEMISTRY OF THE STARS. 



61 



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. 



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

 and X 4630-9 make their appearance in stars at about the temperature 

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

 series, and are present in the stars at the a Eridani stage in the down- 

 ward. 



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

 fiutings of carbon in the violet are replaced by a line at X 4267-5.. 

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

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

 a Eridani to ft Persei on the downside 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. 



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 on 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, 



* Proc. Hoy. Soc., vol. xxx, p. 461. 



