On the Variable Stars of the 5 Cephei Class. 



103 



Name. 



// Aquilse . . . 

 t G-eminorum 

 8 Cephei .... 

 T Yulpeculae 

 S Sagitte . . . 



Magnitude 



Max. Min. 



3 -5 

 3 7 

 3-7 

 5-5 

 5-6 



4-7 

 4*5 

 4-9 

 6 5 

 6-4 



Period. 



d. h. 



7 4 

 10 3 



5 9 

 4 10 



8 9 



Internal from 



minimum 

 to maximum. 



d. h. 



2 9 

 5 

 1 15 

 1 7 



3 10 



Photographed 

 with 

 instrument 

 A. 



Photographed 

 with 

 instrument 

 B. 



The spectra generally extend from near F to K. 



Results of the Preliminary Discussion. 



A careful examination of the negatives has been made by Messrs. 

 Fowler and Shackleton, and five very definite results have been 

 arrived at : — 



(1.) The spectra of the Jive variables of this class which have been 

 photographed are practically identical. 



All the spectra are seen to belong to Group III/? of my classifica- 

 tion of the heavenly bodies.* 



It seems, therefore, that as our knowledge of the spectra of variable 

 stars advances, the association of a particular kind of spectrum with 

 a particular kind of variability becomes more and more evident. 

 This is only what we should expect, since I have adduced evidence to 

 show that the possibility of each particular kind of variability must 

 depend upon the state of condensation of the bodies involved. 



(2.) The five variables in auestion are stars of increasing temperature. 



The spectra are seen to very closely resemble the spectrum of 

 7 Cygni, and I have already stated the evidence which shows that 

 this star, unlike the sun, is increasing in temperature.f 



We have thus revealed to us the fact that these variables, like the 

 other class which I have previously discussed,]; occupy places on the 

 ascending arm of the temperature curve. 



A portion of the spectrum of 8 Cephei, at the time of maximum, is 

 shown on p. 105, where it is compared with the spectra of 7 Cygni and 

 Arcturus. These have been enlarged about ten times from the 

 original negatives taken at Kensington. 



* < Phil. Trans.,' 1893, vol. 184, A, p. 725. 

 f ' Phil. Trans.,' 1893, vol. 184, A, p. 718. 

 t ' Roy. Soc. Proc., 5 vol. 46, p. 401, 1889. 



