M. Arago 071 Double Stars. W 



9, The consequences which result from the nature of the motions which 

 are observed in the Double Stars. And first, As t/tey relate to the 

 universality of the Newtonian attraction. 



The algebraical formulas, by the aid of which we have suc- 

 ceeded in elucidating (ill th curious elliptical movements of the 

 double stars, have been wholly based upon the hypothesis, that 

 the greater nid l«^sser stars attract each other in the inverse ratio 

 of the square of their distances. The determination of the orbit 

 of each star requires only four, five, or at most six measurements 

 of the angle oT posiiwin, together with the apparent distances. 

 With regard to any observations which have not been employed 

 in these primary calculations, whether they be anterior, posterior, 

 or intermediate, they become so many means by which to sub- 

 mit to a delicate and decisive proof, the hypothesis with which 

 we started. It is sufficient to investigate if they be in agree- 

 ment with an orbit which cannot be the true one, if we have 

 deduced its form from an erroneous supposition. We may 

 moreover add, that many of the comparisons have been made 

 betwixt the really observed positions of the satellite stars, and 

 the positions inferred from calculated ellipses. And any dis- 

 crepancies observed, have only been of that minute and trifling 

 character which is nearly inseparable from this difficult kind of 

 measurement. 



Hence, it follows, that in admitting that even to the apparent 

 confines of the visible world, there exists an attractive power 

 which operates in the inverse ratio of the square of the distance, 

 those who calculated the oi-bits of the double stars only assum- 

 ed what was true ; — it follows, that the stars are governed by 

 the same power which, in our solar system, presides over all the 

 motions of its planets and their satellites ; — finally, it follows, 

 that this celebrated Newtonian attraction, the universality of 

 which has not hitherto been established beyond the limits in- 

 cluded within the revolution of the planet most removed from 

 the sun, that is to say, of Uranus, becomes universal, even to 

 the grammatical acceptation of the word. 



It is not to be supposed, that without any hesitation we might 

 have given this indefinite extension to the discovery of Newton. 

 The existence of attraction in all parts of the system, formed by 



