12 M. Arago on Double Stars. 



the sun and the planets which surround him, was a cardinal 

 fact whose laws we had discovered, and whose consequences we 

 had followed with a success truly wonderful. But it did not 

 thence follow that an attractive power was inherent in matter, and 

 that large bodies might not exist in other regions and in other 

 systems, without mutually attracting each other. Reason, how- 

 ever boldly strong, had no right to^ pronounce upon the uni- 

 versality of the law of the square of the distances. Now, how- 

 ever, we repeat it, thanks to the investigations concerning 

 double stars, this hesitation is for ever removed. And this alone 

 would suffice to justify the lively interest which the relative dis- 

 placements of the stars have excited among astronomers. 



We now proceed to exhibit, in the succeeding chapters, some 

 of the other results which this new branch of the science pro- 

 mises to disclose, ^ 



4. When the distances of tlie Double Stars front the Earth shall have 

 been determined, then the masses of those of the Stars whose relative 

 motions are hnown, may be easily compared with the mass of the 

 Earth or Sun. 



Of all the results which constitute the glory of modern astro- 

 nomy, none so much strikes the imagination of those who are 

 not acquainted with the laws of celestial mechanics, as the deter- 

 mination of the masses of the stars. Thus, if it happen that a 

 professor, whose business it is to analyze the various wonders of 

 the firmament to his auditory, is guilty of the mistake at the 

 commencement of a discourse, of citing the numerical values of 

 the planetary masses ; — if, for example, he says, we shall now 

 prove that, supposing we could place the sun in one scale of a 

 balance, to establish the equilibrium, it would require us to place in 

 the other scale 337,000 globes equal in size to the terrestrial globe, 

 —a lively feeling of incredulity would immediately pervade the 

 auditory ; and if subsequently there were any listeners, it would 

 be only to judge of the lecturer's ability to develope a sophism. 

 This is nevertheless the subject to which the natural order of 

 ideas inevitably conduct us. And we feel, without having 

 recourse to any algebraical formulas, that we cannot deny our- 

 selves the gratification of furnishing to our readers an idea, suf- 

 ficiently correct, of the method by whose help we are enabled 



