51 



Hence the luni-solar precession in longitude in 66 years 



= 55 11,3+1,15 da 

 By die Pole Star= 55 25,1 + 2,30 du 



whence is deduced 



Or the luni-solar precession — 55 14,3 + 1,03 da 

 By the Pole Star . = 55 25,1 +2,30 du. 



Hence da = 10",5+2,2 du. 



Or the luni-solar precession = 55 8,6+1,21 rfa 

 By the Pole Star . = 55 25,1+2,30 du 



Hence da = 13",6 + 1,9 du. 



The mean of these three determinations = 12",l+2,0 du. The 

 secular motion therefore =18",3+3,0 du. If we suppose the Pole 

 Star without proper motion in declination, this quantity =18",3, and 

 the motion on the ecliptic =18",3 cos. ob. =:16",8. Mr. Bessel's 

 determination is 14",9.* The exactness of this quantity however 

 depends on the absolute right ascensions in 1755 and 1821, which 



* Astr. Fund. p. 297. 



