CHAPTEK XII 



DOUBLE STAKS AND NEBULAE 



WITH the intuition of genius, Herschel, at an early 

 period in his career, leaped to the conclusion that, as 

 a planet revolves round the sun, so, in the regions of 

 space, stars may revolve round stars, or sun round sun. 

 It was a magnificent idea, apparently beyond proof, 

 and would be reckoned among the useless things of 

 science. " We have already shown," he wrote in 1803, 

 "the possibility that two stars, whatever be their 

 relative magnitudes, may revolve, either in circles or 

 ellipses, round their common centre of gravity; and 

 that, among the multitude of the stars of the heavens, 

 there should be many sufficiently near each other to 

 occasion this mutual revolution, must also appear 

 highly probable." A sun of enormous size and bright- 

 ness revolving round another sun as big or as bright, 

 but it may be of a different colour, might be and really 

 was regarded as the dream of a poet, imagining things 

 that mathematics, with inexorable logic, gave no coun- 

 tenance to. But imagination sometimes realises truth 

 long before the facts of science make it known. It 

 was so here. " I shall therefore now proceed to give an 

 account of a series of observations on double stars, com- 

 prehending a period of about twenty-five years, which, 

 if I am not mistaken, will go to prove that many of 



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