174 A CENTURY'S PROGRESS IN ASTRONOMY. 



visible, while in Ic the hydrogen lines are bright. 

 This class includes the gaseous stars. In 1895, 

 after the recognition of helium in the stars by 

 his assistant, Scheiner, Vogel separated the stars 

 of class 16 from the first type altogether. These 

 stars are sometimes designated as " Type O," and 

 sometimes as helium stars and Orion stars, as 

 the majority of the stars in Orion are of that 

 type. The solar type is divided into two classes, 

 Ila being represented by the Sun, Capella, and 

 other well-known stars, while 116 includes the 

 Wolf- Rayet stars. Secchi's third and fourth 

 types are both classified by Vogel as of the 

 third type. These red stars were specially 

 studied from 1878 to 1884 by Duner at Lund. 

 His results were published in a descriptive cata- 

 logue which appeared at Stockholm in 1884. 

 His researches related to the spectra of 352 

 stars, 297 of Secchi's third type and 55 of his 

 fourth. Duner is perhaps the greatest authority 

 on stars with banded spectra. 



Vogel's classification of spectra is generally 

 adopted by astronomers, although others have 

 been proposed by Lockyer and by Edward Charles 

 Pickering (born 1846), director of the Harvard 

 Observatory. Lockyer's classification was de- 

 signed to fit in with his " meteoritic hypothesis," 

 discussed in the chapter on Celestial Evolution. 



