On the Variable Stars of the 8 Cephei Class. 101 



would readily burn in the air, and, while exhibiting the silicon bands, 

 it would also display the lines of hydrogen, particularly the 0, F, and 

 H lines, the red C being the most conspicuous. Further observa- 

 tions on this spectrum are desirable, and the hydrogen lines should 

 be particularly looked for ; but on the whole I am inclined to believe 

 that Mr. Lundstrom's deduction as to the origin of the " blue name " 

 being caused by silicon is substantially correct, if it be understood 

 that the silicon is in combination with hydrogen. Many of the lines 

 and bands in the Ulfshytte spectrum, which have not been identified, 

 have been observed in the Crewe spectra; but their origin still 

 remains a mystery. 



"On the Variable Stars of the S Cephei Class." By J. 

 Norman Lockyer, C.B., F.R.S. Received November 9, 

 —Read November 21, 1895. 



Introductory. 



Professor E. C. Pickering, in his classification of the variable stars, 

 which is based on a study of the light curves,* recognises two classes 

 of variables having short periods. His Class IY includes those 

 variables, exemplified by 8 Cephei and /3 Lyra?, in which the light 

 changes are not of very great range, and continue throughout the 

 period. Class V comprises those like Algol in which there is a 

 temporary reduction of light at minimum, produced by the eclipse of 

 the bright star by a relatively dark companion ; this explanation has 

 since been established by spectroscopic investigations, which have 

 shown that there is no change in the spectrum at minimum, and that 

 there is an orbital movement of corresponding period. 



Both these classes are sharply distinguished from the variables of 

 the Mira type, which form Pickering's Class II. In this class of 

 variables, as in Class IV, the light changes go on throughout the 

 period, but the range of variation is generally much greater, and the 

 periods are reckoned by months instead of days. The variability is 

 associated in this case with a fluted spectrum (Group II), and in a 

 former communication I have shown that the phenomena can be ex- 

 plained on the supposition that there is one swarm (or more) of 

 meteorites revolving in an elliptic orbit round a central swarm ; an 

 increase of light at maximum occurring at periastron when the 

 number of collisions is greatest.f 



It is probable that the variables of Class IV will require further 

 subdivision, when their spectra have been more fully investigated. 



* 'Amer. Acad. Proc.,' vol. 16, p. 17. 

 f ' Roy. Soc. Proc.,' vol. 43, p. 154, >S87. 



