43 



luni-solar precession =50",38. The polar distance of the Pole Star 

 from the vicinity of the star to the Pole, admits of being determined 

 with great exactness, perhaps more so than that of any other star. 

 Uncertainty in the constant of refraction will not sensibly affect the 

 the result; and as the arch measured is small, the result is less 

 liable to be affected by errors of division. 



The comparison of the computed with the observed places of this 

 star by several astronomers hereafter given, tend to shew the ex- 

 actness of observation. 



The Duke of Marlborough's observations in 1 790, M. Pidzzi in 

 1 800, and the others adduced, appear to confirm the exactness of 

 Bradley's polar distance in 1755. So that if the nonexistence of 

 proper motion in declination be allowed, the quantity 50",38 for 

 luni-solar precession in 1 788 is very exact. 



The stars Rigel and a Orionis are well situate for deducing by 

 the changes in right ascension the quantity of the general preces- 

 sion ; and thence by comparing it with the luni-solar, we obtain the 

 displacement of the ecliptic on the equator. The position of a Cygni 

 is not so favorable. The mean result, from the three, gives the 

 motion in sixty-six years of the ecliptic on the equator = I'i", I. 



The quantity of precession thus found is considerably greater than 

 that adopted by M. Delambre, and greater than that adopted by 

 Mr. Bessel. But it is remarkable that Mr. BesseFs result from tlie 

 declinations of above 2000 stars agrees very nearly with what the 

 Pole Star gives as above. M. Piazzi also has adopted very nearly 

 the same quantity as has been found by the Pole Star. 



