Latitudes of Montjouy and Barcelona, 241 



to each other, unless either or both may have a proper motion, 

 or an annual parallax. But there are other groups, in which 

 the proximity is not apparent, but real ; p^d careful observa- 

 tions have taught us that these stars are physically double ; 

 that they are mutually dependent, mutually attract each other, 

 and form a proper system moving round a common centre of 

 gravity, the smaller star revolving round the greater. These 

 systems, therefore, will occasionally present to a spectator on 

 the earth, the remarkable phenomenon of one star eclipsed by 

 another. The duration of the eclipse may appear considerable, 

 in consequence of the apparent slowness of the motion of the 

 satellite star around its principal. Modern astronomers are 

 already acquainted with several varieties of such phenomena ; 

 Sir Wm. Herschel could not again distinguish the companions 

 of several stars which he had previously seen to be double. 

 Fruitless attempts have recently been made to discover the 

 smaller stars in ^ Herculis and 5 Cygni, long since noticed as 

 double stars. Finally, other stars, (^ Orionis, for example,) 

 which were single, are now become double. It is necessary 

 then to ascertain to which of these classes ^ Ursae Majoris be- 

 longs, before we can assure ourselves that it was a double 

 star at the time the latitude of Montjouy was observed by its 

 means. 



The second reason for investigating this point is an obser- 

 vation of M. Flaugergues, which, if confirmed, would have very 

 important consequences in regard to our general knowledge 

 concerning the stars. It is the only observation of the kind, so 

 far as I am aware, that has ever been publicly stated ; and it 

 happens, curiously enough, to have been made respecting the 

 very star in question. In the * Connoissance des Tems,' for 

 1802, page 360, there is the following notice by M. Flaugergues, 

 whose name is not without authority in astronomical obser- 

 vation : " I have formerly frequently observed the star in the 

 tail of the Great Bear, ^ of Bayer, because I was in the habit 

 of trying the power of telescopes by the apparent distance of 

 that star from Alchor, but without discovering it to be double ; 

 looking at it with a telescope of 15 inches, on the 4th of Au- 

 gust, 1787, at 8 p.m. I saw, with surprise, that it consisted of 

 two stars, one large and the other small, distant from each 

 other the diameter of the smallest, Since that time I have 



