824 Elements in the Sun. 



For a chemical reaction of the type 

 Ti + 2 = Ti0 2 + U, 

 the equation of chemical equilibrium is given by the formula 



io S(i+5ci-.'') = ~«t + ¥" ,o s t+Si,c ' 



which reduces to 



log (I+||^) = "^ST +31ogT + C Ti + 2Co-C Ti „ ! . 

 if, in accordance with the kinetic theory of specific heat, 

 we put {0 P \ i02 = -j . 



This class of chemical reaction is likely to have wide 

 application in the treatment of the spectra of sun-spots, for a • 

 large number of spot-lines were identified by Fowler, Hale, 

 and Olmsted with the band-lines of MgH 2 , Ti0 2 , and CaH 2 

 (Tri-atomic compounds) *. 



It appears that no attention has yet been paid to the study 

 of the spectra of the faculse, which are believed, on the basis 

 of very sound physical arguments, to be regions of higher 

 temperature than the photosphere. Supposing the temper- 

 ature of the faculse to range between 8000° K. and 9000° K., 

 their spectra are likely to show very important differences 

 from the spectra of the ordinary photosphere, and to be 

 similar to the spectra of the Fo to F 5 Gr classes of stars, just 

 as the spectra of sun-spots are similar to those of the Antarian 

 stars (K-class). At any rate, the subject seems to offer a very 

 rich field for investigation. 



If the necessary data be available, these questions will be 

 taken up in a future communication. 



I have much pleasure in recording my best thanks to my 

 students of the Post-graduate classes in Physics for much 

 useful help in the preparation of this paper. 



University College of Science, 



Calcutta. 



May 22, 1920. 



* Pringsheim, Phijsik der So?me, pp. 211 to 217. 



