648 POPULAR SCIENCE MONTHLY. 



But Pickering maintains that, in observations of this kind upon a single 

 star, the precision is such that the reality of the difference, small 

 though it be, is beyond reasonable doubt. 



Taking Pickering's law of change as a basis, Myers has represented 

 the light-curve of U Pegasi on a theory similar to that which he con- 

 structed for Beta Lyrae. His conclusion is that, in the present case, the 

 two bodies which form the visible star are in actual contact. A re- 

 markable historic feature of the case is that Poincare has recently in- 

 vestigated, by purely mathematical methods, the possible forms of re- 

 volving fluid masses in a condition of equilibrium, bringing out a 

 number of such forms previously unknown. One of these, which he 

 calls the apiodal form, consists of two bodies joined into one, and it is 

 this which Myers finds for U Pegasi. 



Quite similar to these two cases is that of Zeta Herculis. This star, 

 ordinarily of the seventh magnitude, was found, at Potsdam, in 1894, 

 to diminish by about one magnitude. Repeated observations elsewhere 

 indicate a period of very nearly four days. Actually it is now found 

 to be only ten minutes less than four days. The result was that during 

 any one season of observation the minima occur at nearly the same 

 hour every night or day. To an observer situated in such longitude 

 that they occur during the day, they would, of course, be invisible. 



Continued observations then showed a secondary minimum, occur- 

 ring about half-way between the principal minima hitherto observed. It 

 was then found that these secondary minima really occur between one 

 and two hours earlier than the mid-moment, so that the one interval 

 would be between forty-six and forty-seven hours and the other between 

 forty-niDe and fifty. The time which it takes the star to lose its 

 light and regain it again is about ten hours. More recent observations, 

 however, do not show this inequality, so that there is probably a rapid 

 motion of the pericenter of the orbit. 



It will be seen that this star combines the Algol and Beta Lyrae 

 types. It is an Algol star in that its light remains constant between 

 the eclipses. It is of the Beta Lyrae type in the alternate minima being 

 unequal. 



From a careful study, Seliger and Hartwig derived the following 

 particulars respecting this system: 



Diameter of principal star, 15,000,000 kilometers. 



smaller « 12,000,000 

 Mass of the larger star, 172 times sun's mass. 

 Mass of the smaller star, 94 times sun's mass. 

 Distance of centers, 45,000,000 kilometers. 

 Time of revolution, 3d. 23h. 49m. 32.7s. 



It must be added that the data for these extraordinary numbers 

 are rather slender and partly hypothetical. 



