232 A CENTURY'S PROGRESS IN ASTRONOMY. 



type stars to Sirian stars, regarded as the hottest 

 stars ; through a second division of solar stars 

 to fourth-type stars. In fact, the theory aspires 

 to give a complete explanation of all celestial 

 phenomena, from meteors to nebulae. Newcomb, 

 however, considers that the objections to the 

 theory are insuperable, and his opinion is shared 

 by the majority of astronomers, many of whom, 

 however, consider that there are elements of 

 truth in the theory ; but Lockyer undoubtedly 

 carried his ideas to an extravagant extent. 



Lockyer's evolutionary order of the stars is 

 not supported by Vogel. Zollner suggested in 

 1865 that yellow and red stars are simply white 

 stars in a further stage of cooling ; but Angstrom 

 showed that atmospheric composition is a safer 

 criterion of age than colour. Vogel's classifica- 

 tion, first published in 1874, and further developed 

 in 1895, is from the standpoint of evolution. He 

 considers Orion stars and Sirian stars to be the 

 youngest orbs. Solar stars are considered by 

 Vogel to have wasted much of their store of 

 radiation, and red stars are viewed as " effete 

 suns, hastening rapidly down the road to final 

 extinction." He considers stars of Secchi's fourth 

 type to be also dying suns, both types represent- 

 ing alternative roads for stars of the Solar type 

 in their decline into dark stars. This view is 



