463 THE LIFE OF JAMES D. FORBES. [CHAP. 



most eminent writers on sidereal astronomy. I should 

 probably have hesitated to oppose my solitary opinion to 

 that entertained by the eminent writers whom I am 

 about to quote, had I not found it to be entirely 

 supported by the eminent authority of two friends to 

 whom I separately proposed it. 



' Nearly a century ago Mitchell computed the chances 

 to be 500,000 to 1 against the stars composing the group 

 of the Pleiades being for tuitously concentrated within 

 the small apparent space which they occupy ; and he 

 thence infers the probability of a physical connection 

 between them. Struve has pushed this consideration 

 much further. In his classification of double stars he 

 has applied the same argument to estimate the improba- 

 bility of the occurrence of even single pairs of stars in 

 close proximity. He "calculates the odds at 9,570 to 1 

 against any two stars from the first to the seventh magni- 

 tude inclusive, falling (if fortuitously scattered) within 4" 

 of each other. Now the number of such binary combina- 

 tions actually observed at the date of this calculation 

 was already 91, and many more have been added to the 

 list. Again, he calculates that the odds against any two 

 stars fortuitously scattered, falling within 32" of a third, 

 so as to constitute a triple star, is not less than 173,524 

 to 1. Now, four such combinations occur in the 

 heavens." Sir John Herschel, from whose Outlines of 

 Astronomy I take this statement of Struve's results, 

 adds, " the conclusion of a physical connection of some 

 kind or other is therefore unavoidable." 1 



' Now, I confess my inability to attach any idea to 

 what would be the distribution of stars or of anything 

 else, if " fortuitously scattered ; " much more must I 

 regard, with doubt and hesitation, an attempt to assign 

 a numerical value to the antecedent probability of any 

 given arrangement or grouping whatever. An equable 

 spacing of the stars over the sky would seem to me to 

 be far more inconsistent with a total absence of law or 



1 ' Outlines of Astronomy, p. '>G4. If I recollect aright, the passage 

 does not occur in the edition in Lardner's Cyclopaedia.' 



