450 



Mr. J. Norman Loekyer 



Type 16 are stated as " spectra in which the hydrogen lines and 

 the few metallic lines all appear to be of equal breadth and of 

 sharp definition."* It is on the ground of this greatly modified 

 definition that a Cygni is included with stars like Rigel in Class 16. 



Dr. Vogel, however, is not prepared to accept Dr. Schemer's 

 amended definition of Class 16. He writes : " However justifiable 

 it may be to regard the peculiarly sharp spectral lines of the stars 

 above mentioned and a few others of the same kind as worthy of 

 special consideration, the adoption of this proposal would make it 

 necessary to separate a number of stars (including those of Orion) 

 whose relationship is placed beyond all question by the investigations 

 I have referred to, and to place them with a Cygni, which has a 

 materially different spectrum." f 



In the same paper Dr. Vogel brings forward a new definition of 

 his Class 16 in the following terms : " Spectra in which, besides the 

 still dominant hydrogen lines, the lines of cleveite gas appear, and 

 above all the lines X 4026, X 4472, X 5016, and X 5876(D 3 ). The lines 

 of calcium, magnesium, sodium, and iron are also more or less 

 numerous in spectra of this subdivision." 



This new definition excludes a. Cygni from Class 16 in Dr. Vogel' s 

 opinion, and he places this star in Class la 3 of his extended classifica- 

 tion of spectra of the first class. This sub-class is thus defined : 

 "Spectra in which the calcium line X3934 has nearly the same 

 intensity as the hydrogen lines. In occasional instances it is still 

 sharply defined at the edges, or it may be broader and more intense 

 than the hydrogen lines, and very diffuse, forming with the hydrogen 

 line He(X 3970), which is greatly intensified and broadened by the 

 calcium line X 3969, a conspicuous pair. 



" In the spectra of this division the lines of the cleveite gas cannot 

 be recognised ; on the other hand, numerous strong lines of different 

 metals, particularly lines of iron, are always present. The lines of 

 hydrogen are still always dominant. H$ is plainly apparent among 

 the other lines, and the group Gr is less conspicuous than H y . This 

 subdivision forms the direct connecting link with the spectral 

 class II, in which the hydrogen lines no longer play a prominent part 

 in comparison with the lines of other metals. "J 



According to this definition, ac Cygni is classed with Procyon, a 

 star which in the main resembles the sun, and this notwithstanding 

 Scheiner's remark that the spectrum of « Cygni bears no resemblance 

 to that of the sun. 



It is clear, then, that oc Cygni cannot be classified satisfactorily on 

 the supposition that all stars are cooling. 



* Schemer's 'Astronomical Spectroscopy' (Frost's translation), p. 245. 

 + ' Astrophysical Journal ' (1895), vol. 2, p. 343. 

 t ' Astrophysical Journal ' (1895), vol. 2, p. 344. 



