THE LIGHT OF THE STAKS. 185 



obeyed a different law from the second, fourth, 

 sixth, and eighth. Duner proved that two stars 

 revolve round their centre of gravity in less 

 than three days, alternately occulting each other, 

 while the ellipticity of the orbit explains the 

 irregularity of the light changes. In April 1900 

 Duner gave his final conclusions as follows : 

 " The variable star Y Cygni consists of two stars 

 of equal size and equal brightness, which move 

 about their common centre of gravity in an 

 elliptical orbit, whose major axis is eight times 

 the radius of the stars/' He also stated the 

 exact period of revolution and the eccentricity 

 of the orbit. 



In the case of the short - period variables, 

 such as ft Lyrae, 8 Cephei, Geminorum, and 

 T) Aquilae, the variations do not seem to be 

 due to eclipse. It was discovered by Professor 

 Pickering that ft Lyrse is a spectroscopic 

 binary, but Vogel and Keeler showed that 

 the supposed orbit is incompatible with the 

 eclipse theory. Vogel says : " I am convinced 

 that ft Lyrse represents a binary or multiple 

 system, the fundamental revolutions of which in 

 12 days 22 hours in some way control the light 

 change." The eclipse theory, however, is still 

 maintained by Belopolsky, who has framed a 

 hypothesis according to which the chief minimum 



