492 BEI.L SYSTEM TECHNICAL JOURNAL 



those elements if present would be totally ionized and would not reveal 

 their familiar lines at all. Rubidium was thought to be omitted from 

 the composition of the sun, until it occurred to H. N. Russell to look 

 for its lines in the spectra of comparatively cool sunspots. The relative 

 intensities of the lines of ionized and non-ionized atoms of various kinds 

 in the spectra of indix'idual stars are now ascertained and used as a 

 guide in assigning temperatures to these stars, and their guidance is 

 shown reliable by the accord between the conclusions to which it leads 

 and conclusions otherwise attained. The study of ionization in the 

 laboratory thus contributes to the understanding of the stars. 



