WEIGHING THE WORLDS 



quirements of the explanation, thus making it vir- 

 tually certain that the explanation is correct. 



In recent years large numbers of spectroscopic 

 binaries have been observed, the periods of which 

 vary from 1.45 days to a term of years. The shift 

 of the spectroscopic lines determines the speed of 

 the star, and this makes it possible to compute the 

 actual orbit, provided the star is one of measured 

 parallax. Such is the case, for example, with Miss 

 Maury's first spectroscopic binary Mizar. Vogel's 

 later test showed that the period of this star is about 

 twenty and one-half days. Taken in connection 

 with the size of the orbit this shows that the mass 

 of the pair is about twenty times that of the sun. 

 Here, then, is a case in which the presence of an 

 absolutely invisible body enables the astronomer to 

 determine the aggregate mass of that body and its 

 bright companion. It is not possible, however, by 

 any means at present known to determine with pre- 

 cision the relative mass of the two components. But 

 it is a sufficiently wonderful achievement to demon- 

 strate the existence of a dark star and to gain even 

 an approximate knowledge of its weight. 



Indeed, it is hard to conceive of any unexplored 

 field of astronomical discovery that can have a 

 greater wonder than this in store for us. 



SOME INTERESTING STAR-GROUPS 



The dark stars have peculiar interest because of 

 what they reveal as to star groupings that have 

 greater or less resemblance to the mechanism of the 

 solar system. 



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