LIBRARY 



NEW YO'r- • 



BOTANICAL 



GARDEN 



XI. — The Parallax of rj Cassiopeise, deduced from Rutherfurd 



Photographic Measures. 



BY HERMAN S. DAVIS. 

 Read Feb. 4, 1895. 



Between July 30, 1870, and December 21, 1873, twenty-seven 

 negatives of the stars about vj Cassiopeise Avere taken by Ruther- 

 furd. The conditions of exposure and, indeed, even the dates, as 

 well as also the methods of measurement and of reduction are 

 almost identical with those of fi and 6 Cassiopeia already reduced 

 for parallax.* Hence reference to that paper will make clear the 

 plan followed in the application of corrections for division errors, 

 the " tangent correction," for refraction and for aberration. 



The observations have been reduced to the epoch 1872.0, using 

 AuwERs' proper motion which is 



J« = + o\i346 Jo = — o."48i, 



corresponding to a motion of i."i965 on a great circle whose 

 position angle is 113° 42' 10". Representing this motion by o 

 (expressed in terms of one division of the glass scale as a unit of 

 measure = 0*^.042712) and the angle by ^ at the time 1872.0, the 

 time of observation b^' t, the position angle of the star relative to 

 7j Cassiopeise by p and its distance by s after the corrections 

 named in the first paragraph have been applied, we computef 



P) 



*The Parallaxes of i-i and Cassiopeite, deduced from Rutherfurd Photo- 

 graphic Measures. By Harold Jacoby. Annals N. Y. Acad. Sci., Vol. VIII., 

 p. 1. 



tlbid., p. 3. 



Annals N. Y. Acad. Sci., VIII., April, 1895.— 22 



