240 On a new Calculation of the 



archives of the observatory ; nor is there any allusion to it in 

 any of the numerous writings in which M. Delambre returned 

 to the discussion of these anomalies. It requires a telescope 

 of considerable power to distinguish the stars apart ; those of 

 the ordinary repeating circles, which I have examined, do not 

 separate them. We cannot now examine the particular circle 

 employed by Mdchain for this star, as he parted with it to the 

 astronomers of Milan, when on his return to France ; but 

 we have still at the observatory the circle supplied at the same 

 time and for the same purpose to Delambre, and we know 

 that the dimensions of these instruments were so nearly the 

 same, as to justify the application to the one of a conclusion 

 drawn from, the other. Now the telescope of this circle does 

 not separate the stars, but represents them conjointly, under the 

 appearance of a single ill-defined star : nevertheless the com- 

 panion of ^ if it were alone in space, is of sufficient magnitude 

 to be visible to the unassisted eye of a good observer ; but the 

 proximity to a luminous point much exceeding the object itself 

 in brilliancy, causes the light of the two to be confounded, until 

 the distance between them becomes sufficient for separation. 

 Hence it follows that the point actually observed by M^chain 

 must have been some apparent centre between the two stars, 

 nearest to the largest, but in what proportion it may not be 

 easy to say : we may content ourselves, at present, by re- 

 marking the direction in which a correction arising from this 

 cause should be applied ; its effect must obviously have been 

 to increase the zenith distances of the observations below the 

 pole, and to diminish those above the pole. 



Before we can fully admit this conclusion we must, how- 

 ever, assure ourselves that ^ Ursse Majoris was really double, as 

 seen from the earth, at the time Mechain observed. This might, 

 perhaps, appear an unnecessary question ; but there are two 

 causes (one of which, at least, is sufficiently remarkable) which 

 require its examination. The first is grounded on the pro- 

 perties which modern observers have recognized in double stars. 

 When two stars are nearly in the same direction as seen from 

 the earth, but at very unequal distances from it, they appear 

 as two luminous points very close to each other ; but their 

 proximity is only apparent, being an effect of projection. In 

 this case the stars preserve always the same relative position 



