244 On a new Calculation of the 



ever, this consideration, and confining myself simply to 'the 

 two points which it is my purpose to clear up, I believe that 

 we may conclude with full confidence, that the star ^ Ursse 

 Majoris was double, and presented the same appearance as at 

 present, when M. Mt^chain observed it at.Montjouy and 

 Barcelona. 



I pass to the general examination of the observations from 

 which the latitudes were deduced, and to their recalculation. 



The stars which M. Mechain employed at Montjouy were 

 a and /3 Ursse Minoris, ^ Ursse Majoris and a Draconis, /3 Tauri 

 and Pollux, being six in all. The four first are circumpolar, 

 and pass the meridian on both occasions north of the zenith ; 

 these were observed both above and below the pole. The two 

 last, from their declination, could only be observed on the 

 southern meridian. 



At Barcelona we find employed a and /3 Ursae Minoris, 

 5 Ursse Majoris and Pollux : a Draconis and /3 Tauri were not 

 observed, but Capella in their stead. At this station, there- 

 fore, there were four stars north of the zenith, of which three 

 were circumpolar ; and one only to the south of the zenith. 



All these stars are not equally well situated in respect to the 

 accuracy of the results that might be obtained with them. 

 We should scarcely deem, at the present day, the selection 

 equal to a determination so important as the latitude of 

 one of the extremities of an arc of the meridian. Some, by 

 being too near the zenith, give too great a value to errors 

 arising from defect in verticality of the plane of the circle, and 

 these also in their passage below the pole descend to zenith 

 distances so great, as to be affected by irregularities of refrac- 

 tion : a and (S Ursse Minoris, (3 Tauri and Pollux, unite nearly 

 all the conditions that make them suitable ; but Capella, ^ 

 Ursse Majoris, and a Draconis are at zenith distances not 

 greater than 4^°, 14J°, and 16J° in passing the meridian above 

 the pole ; and the two latter pass below the pole at the low 

 altitudes of 16° and 7^. 



Some of the errors which might be looked for from these 

 causes, appear to have been remarkably kept within limits by 

 the great skill and pains of the observer; but it was not in his 

 power to destroy them altogether, and those which remain ne- 

 cessarily exercise all their influence on the results, in conse- 



