DOUBLE STARS. 281 



relative position can be incontestably proved. 15 The earliest 

 comparison gave one-sixteenth, the most recent gives one- 

 ninth, as the proportion of the cosmical bodies which, by an 

 observed motion both of the primary star and the companion, 

 are manifestly proved to be physically double stars. 



Very little has as yet been numerically determined re- 

 garding the relative distribution of the binary star-systems 

 throughout space, not only in the celestial regions, but even 

 on the apparent vault of heaven. In the northern hemi- 

 sphere, the double stars most frequently occur in the direction 

 of certain constellations (Andromeda, Bootes, the Great Bear, 

 the Lynx, and Orion). For the southern hemisphere Sir John 

 Herschel has obtained the unexpected result "that in the 

 extra -tropical regions of this hemisphere the number of 

 multiple stars is far smaller than that in the corresponding 

 portion of the northern." And yet these beautiful southern 

 regions have been explored under the most favourable cir- 

 cumstances, by one of the most experienced of observers, 

 with a brilliant twenty-feet reflecting telescope which sepa- 

 rated stars of the 8th magnitude, at distances even of three- 

 quarters of a second. 16 



5 The number of fixed stars in which proper motion has 

 been undoubtedly discovered (though it may be conjectured 

 in the case of all) is slightly greater than the number of 

 double stars in which change of position has been observed. 

 (Madler, Astr., s. 394, 490, and 520-540.) Results obtained 

 by the application of the Calculus of Probabilities, according 

 as the several reciprocal distances of the double stars are 

 between 0" and 1", 2" and 8", or 16" and 32", are given by 

 Struve, in his Mens microm., p. xciv. Distances less than 0**8 

 have been taken, and experiments with very complicated 

 systems have confirmed the astronomer in the hope that these 

 estimates are mostly correct within 0"-1. (Struve, ilber Doppel- 

 sterne nach Dorpater Beob., s. 29.) 



16 Sir John Herschel, Observations at the Cape, p. 166. 



