On the Chemistry of the Hottest Stars. 175 



Map IV. — Temperature ranges of different substances. 



shorter range, iron and the cleveite gases ; the enhanced lines of the 

 former being interpolated about half way np the long stages of 

 calcium and hydrogen, and the lines of the cleveite gases near the top. 



The map also indicates the relative temperatures at which the 

 changes in the spectra of different substances take place. 



With special regard to iron, it may be noted that the fundamental 

 change in its spectrum occurs at about the temperature of ac Cygni,. 

 while the enhanced lines of calcium are unaffected at that tempera- 

 ture. 



VIII. Inversion of the Phenomena on Cooling in the case of 

 the Metallic and Cleveite Lines. 



The Temperature Curve. 



In my previous investigations, both visual and photographic, of 

 stellar spectra, I was led to conclude, in opposition to Vogel's view, 

 that some stars are becoming hotter, *while others are becoming 

 cooler.* 



I first suggested a temperature curve in 1887, f on the left side of 

 which are placed stars of increasing temperature, while the cooling 

 stars occupy the right hand side, the highest temperature occupying 

 the highest part of the curve. 



* 'Eoy. Soc. Proc.,' vol. 43, p. 145; iUd. t vol.45, p. 309; 'Phil. Trans.,' A>. 

 vol. 184, p. 709. 



f 1 Eoy. Soc. Proc.,' vol. 43, p. 144. 



