M. Arago on Double Stars. 9 



tion corresponding to known epochs, will be indispensable in 

 calculating the form of the orbit of the lesser star. 



It was not meant to give in this place even the slightest 

 idea of the algebraical calculations which serve for the solution 

 of the problems relative to the form and the position of the or- 

 bits of double stars. We must be content with reporting the 

 results. The first to which we have arrived, viz. the elements 

 of the orbit of the stellary satellite of | of the Great Bear, have 

 been obtained by M. Savary, of the Bureau des Longitudes, by 

 methods which are peculiar to himself. The others are the re- 

 sults of the labours of MM. Bessel and Encke, and of Sir John 

 Herschel. 



Amongst these stars, there is one, the consort of *j of the 

 Crown, which has accomplished the entire circuit of its orbit, 

 since Sir W. Herschel determined, for the first time, its angle of 

 position. It is already considerably advanced in its second re- 

 volution. The oldest observations of the Great Bear, re- 



• This column contains theTatio of the eccentricity (that is the distance 

 of the centre of each ellipse from the focus) to half the greater axis. In our solar 

 system, the greatest values of these ratios are, for Mercury, 0.21 ; for Pallas, 

 0.24 ; for Juno, 0.25. In the other eight planets, the eccentricity is in each 

 less than 0.1. The orbits of the seven stars exhibited in the above table are, 

 then, much more elongated, much more different from a circle, than those of 

 the eleven known planets. This result is certainly worthy of remark, but 

 it ought not very much to astonish us. The masses of the planets of our 

 system are but very small fractions of the mass of the sun ; whilst in the 

 double stars, the satellite star and the central one may be bodies of equal di- 

 mensions, or at least of the same class of magnitude. We may add that agree- 

 ments of this sort may one^day become the true touchstone of cosmogonic 

 theories. 



