II. Method of Reduction. 



Precession. — The epoch selected was 1875, that being very- 

 near the mean of the dates at which the plates were taken. 

 The precession factors were computed by Professoi Hill's for- 

 mulae as given in the '^Star Tables of the American Ephemeris," 

 Wash., 1869, pp. xviii, xix. The constants used were those of 

 Peters and Struve, being, for 1800 



m=^ 3^ .07082-!- ^ooo 01899;? 

 n = 20^^.0607 — ■'^.000 0863A 



Introducing these values in Hill's formulae, we obtain for 1875, 

 the numbers in brackets denoting logarithms : 



^— = 3^o7225 -|- [o. 1 261 15] sill a tan ^ ■\- fi 



d6 

 ^= [1.302206] cos a -\- fj.^ 



- + [5-98778 — 10] (" '^- -\- jJ- J cos a tan 6 



/d6 \ 



+ [4.81 169 — 10] ( -TT + /"^ ) sin a sec2 6 



-f- [4.9866 — 10] [ifi^ tan 8 

 -\- o.'ooo 032 210 



-^ = [4.63380,.- 10] (^-^^-/.^j . 



+ [7.i6387„— lo](^^ + ^J sin a 

 + [6.7367^ — 10] ^.2 sin 2rf. 



The third term, both in right ascension and in declination, was 

 taken from Kloock's " Tafebi der Praecession,'' that being 



(12) 



