CHAPTER XXIX 

 THE ASTRONOMY OF THE INVISIBLE 



WHEN the pattern of our solar system has been made out, it 

 was the most natural thing in the world to suppose that count- 

 less other systems were cut out more or less in the same fashion. 

 The scheme was engagingly simple a giant sun at the centre, 

 with a gay retinue of little planets skimming round about his 

 worshipful majesty and deriving from him their sustenance and 

 the order of their lives. 



There came a* rude jostle when the astronomers discovered 

 that there might be systems with two huge suns. With minds 

 attuned to a sense of unitary dominance, the " star " system, 

 let us say, the idea of divided primacy seemed as incongruous 

 as would a performance of Hamlet with two counterfeits of 

 the melancholy Dane. But the fact could not be denied. 



Herschel had demonstrated that double-star systems actually 

 exist. But little progress was made until the subject was taken 

 up by the two great parallax hunters, Struve at Dorpat and 

 Bessel at Konigsberg. It followed very naturally from their 

 study of stellar distance, wherein the accurate determination 

 of the position of a star was of fundamental importance. If 

 through a period of years two carefully located stars were found 

 to separate slightly, then draw together again, it was a fair 

 inference that they were in reality revolving one around the 

 other. It seems a slender thread to build upon. But such a 

 quantity of evidence has come subsequently as to permit no 

 question. 



Some of these double-star orbits, especially those surmised 

 by Herschel, are so vast, they can as yet only be guessed at 

 vaguely. Some twenty-eight or thirty are known with periods 

 of less than a hundred years, and therefore with more or less 

 certitude. 



It is a matter of very curious interest to note that in two 



of the best known of these revolving pairs the companion sun 



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