IT. — The Parallax of 61 1 Gygni, deduced from the Rutherfurd 

 Photographic Measures. 



By Eerman S. Davis. 



Read May 3d, 1897. 



32. For the purpose of determining the parallax of 61 1 Gygni 

 the measures of both distance and position-angle have been used 

 as recorded in the preceding catalogue of sixty-five stars. The 

 method adopted for getting the parallax from the measures of 

 distance is the same as has been used in previous investigations at 

 this Observatory.* Briefly stated this consists of correcting the 

 observed distances for refraction, aberration, errors of the scale, 

 proper motion of 61 1 Gygni, etc. These distances so corrected 

 may be obtained from Table V by taking the sums of the quan- 

 tities in columns eight, nine and ten. These sums are printed in 

 columns two and three of Table XVI. 



33. Then particular pairs of comparison stars were so chosen 

 that their components should be as nearly as possible equally 

 distant from 61 1 Gygni and differing 180 in position-angle. 

 Table XIY contains a catalogue of these stars with memorandum 

 of some other observers who have used the same stars for de- 

 termining the parallax of 61 Gygni. 



In the equations of condition of Table XVII have been intro- 

 duced an unknown y varying with the time, as a correction of the 

 assumed proper motion ; and another unknown x, as the correc- 

 tion of the assumed mean of the distances. The coefficients of the 

 parallax have been obtained as follows: Using the symbols of 

 paragraph 14, the quantities of column eleven, Table V are 



£3 -P3 + Si A- 

 Denoting by primed letters all symbols belonging to the less 

 distant of the two comparison stars of each pair, we have as the 

 coefficient of the parallax 



(S, P, + S, P,) — {S 3 ' P s + S,' P<) 



when the absolute term of the equations is the difference of the 

 distance of the comparison stars from 61 x Gygni, after these dif- 

 * The Parallax of fJ. and Cassiopeia, by Harold Jacoby. 

 The Parallax of v Cassiopeise, by Hekmax S. Davis. 



