On the Classification of Stars of the 8 Cepliei Class. 449 



lines which are strongly marked in the spectrum of o Cephei as com- 

 pared with corresponding lines in the solar spectrum photographed 

 with the same instrument. A discussion of these differences shows 

 that the more special lines of & Cephei, like those of a. Persei, are 

 very prominent in oc Cygni. 



In spite of these differences, Dr. Schemer classes a. Persei with 

 stars like the sun, but regards it as a transition stage between a Cygni 

 and the sun. He says : " From the general conclusions, the above 

 list gives us quite a curious and important result. If one compares 

 these lines with those in the spectrum of a. Cygni, which is of special 

 interest as an advanced spectrum of Class 16, one finds that, out of 

 sixty lines in <x Cygni, twenty-one occur in the list, and all of these in 

 a. Persei. The fact, therefore, remains that nearly half the lilies which 

 in the spectrum of a. Persei show divergences when, compared with 

 the solar spectrum appear certainly in any case in the spectrum of 

 ex. Cygni and determine its peculiarity. 



" Now a Cygni belongs to Class 16, a. Persei to Class Ila, and the 

 plausible conclusion appears to me, therefore, that a. Persei had pre- 

 viously a spectrum similar to that of oc Cygni, and that in this case 

 we have the missing connexion between 16 to Ila." * 



The spectrum of a. Tauri, which, as I shall show, must be regarded 

 as a condensing swarm, closely resembles that of the sun ; so that 

 Dr. Schemer's evidence would equally place a. Persei intermediate 

 between a. Tauri and a Cygni. 



Difficulties connected ivith VogeVs Classification. 



The close association of stars like ■£ Cephei with those like a. Cygni 

 makes it here important to discuss the place of <x Cygni in Vogel's 

 classification. With regard to this star Dr. Scheiner writes : " The 

 spectrum of a Cygni, in spite of the large number of its lines, has no 

 resemblance with that of the sun. While it is possible to identify 

 most of the lines with solar lines in respect of their position, yet the 

 total lack of agreement as to intensity of the lines makes many of 

 these identifications worthless." f 



Dr. Scheiner has classified a. Cygni in Yogel's Class 16, which w r as 

 thus defined in Yogel's original classification: "Spectra in which 

 the metallic lines are few in number, and very faint or entirely 

 imperceptible, and in which the hydrogen lines are lacking." 



In view of the photographic results obtained at Potsdam, the 

 last clause in this definition was corrected in 1888, so that it reads : 

 " and the strong hydrogen lines of Type la are lacking. "J This has 

 again been modified by Dr. Scheiner, and the characteristics of 

 * ' Potsdam Observations,' vol; 7, Part II, p. 331. 



f Schemer's ' Astronomical Spectroscopy ' (Frost's translation), p. 247. 

 X ' Ast. Nach.,' vol. 119, p. 97. 



