382 Rutherfiird Photographic Pleasures. 



in the previous Ruth erf ard Pleasures. It is proper to add in this 

 connection that these* tables were computed by Professor Jacoby, 

 Mho had to this extent begun the reduction of these star-positions 

 previous to his departure to Europe. After the completion of 

 tlie Pai'allax of r^ Cassiopeia^ these tables, together with the 

 original measiyes, were placed in u\y hands by Professor J. K. 

 Rees that I might finish the discussion thus begun. 



The corrections for precession, nutation and aberration have 

 been computed by the formula? of page 267, Jacoby's Pleiades, 

 which b}' the substitution of the coordinates of rj Cassiopeia? be- 

 come in this case 



^^70 = +i3+[o.822„].4 + [o.258,]£+[o.i83j6'+[9.444„]i>. 



~lp7i = + 7 + [o.822„]J + [o.258j5+[o.i83jC+[9.444ji). 



Jp,^ = o-i-[o.822jJ-f [o.258n]5-f [o.i83jC'+[9.444„]Z>. 



-^7^7 3 = - 7+[o.822„].4-f[o.258j5-f [0.183,,] C-f[9.444„]/>. 



where Jj^^o denotes the correction to be applied to the position 

 angle for the plates made in 1870, and so on in the other years 

 as denoted bv the subscripts. The factor for the correction of the 

 distance is 



~ = [4-350] G + [4.4i3„]i). for all years. 



The numerical values of these quantities are given in columns 

 two and three respectively of Table III.; the}- are additive to the 

 observed quantities, and will reduce them to 1S72.0, for which 

 time the coordinates of r^ Cassiopeia? are 



a = 6^ 41"' 22.-'io8 

 J = 57 ^'8' io."50 



based on Auwers' position and proper motion in the Fundamen- 

 tal Catalog. 



In the second portion of Table III. is given the mean of the 

 East and West zero-corrections computed for each by the 



formula* 



V ^=^ k z tan — y-hx 



in which v is the zero-correction to be added to all observed i)Osi- 

 tion angles of each plate. 



*Annals X. Y. Acad, of Sci., Vol. VI., p. 272. 



1 



