118 Rutherfurd Photographic Measures of 



which may be computed for each plate separately after Jtf fl has 

 been computed by the preceding formula; and where the value of 

 z is obtained from the following relations :* 



z = A — 1/. 



\' = i8o° — ~ — a sin tt tan S 



COt I = : 5 — COt (7T — Xq). 



By substitution of the constants for these stars these become : 

 V = 6 5 °iS'i6".5 



cot \ = 21.75560 0.509789 



'Po 



hence 



z = % — 6s°i8'i6".5 



which may be computed for each plate. 



Thus the variation in distance due solely to the proper motions 

 of 61 1 and 61 2 Gygni in the assumed direction at the assumed 

 rate may be expressed by 



A<7 + A\ 



as computed for each value of r, and printed in columns nine and 

 ten of Table XIII. This quantity is additive to the observed 

 distance on each plate to reduce to the mean epoch. 



31. By the formula of paragraph 17 may be computed values 

 of K or J/ applicable to the new mean epoch adopted, thus : 



A .A'o= [9-7895] T7> 



where the number in brackets is a logarithm as usual. 

 We also have, as in paragraph 30, 



and 



COt A / 7T„ = - - — —2 — — COt (Xn — z ) 



rp/ sinUo' — z) yA0 



coty= . , ' ° r — cot (> — Xo) 



a sm (7r — Xo ) 



* Jordan : Handbuch der Vermessungskunde, 4te Auflage. Bd. Ill, § 359, 3 \z . 



