RESULTS OF DOUBLE STAR OBSERVATIONS MADE 



WITH THE EQUATORIAL OF THE MORRISON 



OBSERVATORY. 



Henry S. Pritchett. 



During the summer of 1896, by permission of the Director, 

 Professor C. W. Pritchett, I was enabled to use the 12^ inch 

 equatorial of the Morrison Observatory in observing double 

 stars. The following observations made at that time were in 

 continuation of a systematic series of measures of double 

 stars begun at this observatory in 1880. 



The observations made in 1880, 1881 and 1884, together 

 with a description of the instrument, the method of observing 

 and the value of the micrometer screw are printed in Vol. I. 

 of the publications of the Morrison Observatory. 



It may be said in brief that the eyes were held so that the 

 line joining them was either parallel to or perpendicular to the 

 line joining the stars. 



Just before the measures were begun the micrometer had 

 been fitted with Burnham's illuminating apparatus, a gift to 

 the observatory from its founder, Mrs. Morrison-Fuller. 



An observation on each night consisted of from 3 to 5 

 settings of the position-circle and two readings of the double 

 distance. 



PROBABLE ERROR. 



The probable error of a single observation, both in posi- 

 tion-angle and distance, is shown in the following table. The 

 observations have been separated into two groups, the first 

 including all measures in which the distance was less than 2", 

 and the second, measures in which the distance exceeded that 

 limit. 



These groups are denoted below by the letters A and B, 

 and the probable errors in position-angle and distance by p, 



(299) 



