THE PARALLAXES OF FIFTY STARS (SECOND LIST) 

 DETERMINED AT SPROUL OBSERVATORY. 



By JOHN A. MILLER, 



WITH THE COOPERATION OF 



JOHN H. PITMAN and HANNAH B. STEELE. 



{Read December 5, 1919.) 



I have given in the following pages the data of observation, the 

 data of reduction and the reductions necessary to determine the 

 parallaxes of fifty stars. It seems unnecessary to describe either 

 the instruments or the methods employed in the work, further than 

 to say that the intsruments used are the same that were used in de- 

 termining the parallaxes of the first list published by the observatory 

 in 1 91 7 (Sproul Observatory Publication No. 4). The fields are 

 photographed with a 24-inch visually corrected refracting telescope 

 on Instantaneous Isochromatic plates. A ray filter which cuts off 

 the violet and the red rays is placed very near the plate. These 

 plates are measured and reduced as described in the publication re- 

 ferred to. The scale on the plate is 4".685 to the quarter millimeter, 

 the value of one turn of the screw on the measuring engine. 



These results have been obtained through the efforts of several 

 persons. The work has been done according to plans of the writer. 

 Those participating in the work are : Professor John H. Pitman, 

 Ivliss Hannah B. Steele, Dr. Samuel G. Barton, Reverend Walter A. 

 Matos, Miss Marie S. Bender, and Miss Caroline H. Smedley. No 

 one of us has been free to devote his entire time to it. I believe, in 

 the body of the text, I have given specific credit to each for the part 

 of the work he has performed. The reductions and many of the 

 measures, as well as the routine work of marking the plates and 

 keeping the records was performed by Miss Steele until 1916 when 

 she went to Yerkes Observatory. Miss Bender did this work the 

 following year and Miss Smedley, since the summer of 1917, has 

 given much of her energies to the same work. 



Some of the fields of comparison stars have been selected in ac- 



85 



PROC. AMER. PHIL. SOC, VOL. LIX, F, MARCH 30, I92O. 



