CHAPTERS ON THE STARS. 645 



That is to say, the partial eclipses at intervals of six and one-half days 

 are not equal. At the alternate minima the star is half as bright 

 again as at the intermediate minima. 



It is impossible to explain such a change as this merely by the in- 

 terposition of a dark body, and this for two reasons. Instead of re- 

 maining invariable between the minima, the variation is continuous 

 during the whole period, like the rising and falling of a tide. More- 

 ever, the inequality of the alternating minima is against the theory. 



Pickering, however, found from the doubling of the spectral lines 

 that there were two stars revolving round each other. Then Prof. 

 Gr. W. Myers, of Indiana, worked out a very elaborate mathematical 

 theory to explain the variations, which is not less remarkable for its 

 ingenuity than for the curious nature of the system it brings to light. 

 His conclusions are these: 



Beta Lyrae consists of two bodies, gaseous in their nature, which re- 

 volve round each other, so near as to be almost touching. They are 

 of unequal size. Both are self-luminous. By their mutual attraction 

 they are drawn out into ellipsoids. The smaller body is somewhat 

 darker than the other. When we see the two bodies laterally, they are 

 at their brightest. As they revolve, however, we see them more and 

 more end on, and thus the light diminishes. At a certain point one be- 

 gins to cover the other and hide its light. Thus the combined light con- 

 tinues to diminish until the two bodies move across our line of sight. 

 Then we have a minimum. At one minimum, however, the smaller and 

 darker of the two bodies is projected upon the brighter one, and thus di- 

 minishes its light. At the other minimum, it is hiding behind the 

 other, and therefore we see the light of the larger one alone. 



This theory receives additional confirmation from the fact, shown 

 by the spectroscope, that these stars are either wholly gaseous, or at 

 least have self-luminous atmospheres. Some of Professor Myers's con- 

 elusions respecting the magnitudes are summarized as follows: 



The larger body is about 0.4 as bright as the smaller. 



The flattening of the ellipsoidal masses is about 0.17. 



The distance of centers is about If- the semi-major axis of the larger 

 star, or about 50,000,000 kilometers (say 30,000,000 miles). 



The mass of the larger body is about twice that of the smaller, and 

 9£ times the mass of the sun. 



The mean density of the system is a little less than that of air.* 



It should be remarked that these numbers rest on spectroscopic re- 

 sults, which need further confirmation. They are, therefore, liable to 

 be changed by subsequent investigation. What is most remarkable is 

 lhat we have here to deal with a case to which we have no analogy in 



* 'Astrophysioal Journal', Vol. VII, January, 1898. 



