218 THE NEW KNOWLEDGE. 



contained in them, and the running-down of temperature 

 is measured by the progressive contraction of the spectra of 

 the stars towards the red end of the spectrum. The chemical 

 constitution of the stars is thus correlated with their tem- 

 perature, and the stellar thermometer, page 209, is an expres- 

 sion of this correlation. But when Lockyer had sorted 

 out his stars into equal-temperature groups in accordance 

 with this table, he discovered a fact of the utmost impor- 

 tance and significance. He discovered, indeed, that the 

 constituent stars of each one of these groups having among 

 themselves the same elements, the same length of spectrum 

 and, consequently, the same temperature, differed in this, 

 that while some of them had thick hydrogen lines and thin 

 metallic lines in their spectra, in others the relative thick- 

 ness and thinness of the lines was reversed. The different 

 intensities of the hydrogen lines in stars of practically iden- 

 tical temperature and constitution is shown in the accom- 

 panying Fig. 53 in the case of Sirius and alpha-Cygni to- 

 gether with the differences in width and intensities of the 

 enhanced metallic lines in two other similar stars Procyon 

 and gamma-Cygni. 



For the full bearing of this fact the reader is referred to 

 Lockyer's "The Meteoritic Hypothesis." Here it will suf- 

 fice to say that this fundamental difference of intensity in 

 the spectral lines of stars of the same temperature and 

 constitution leads logically to the conclusion that while 

 those stars having thick hydrogen lines and thin metallic 

 lines are decreasing in temperature others in which the rel- 

 ative intensities of the lines are reversed are on the con- 

 trary increasing in temperature. 



In other words, while some of the stars are growing 

 cooler and more complex, and are undergoing an evolution, 

 others are growing hotter and less complex and are under- 





