V. — The Rutherfurd Photographic Measures of the 

 Stars about fi Gygni. 



BY HAROLD JACOBY. 



Bead April 4, 1892. 



The group of stars surrounding j3 Cygni was frequently photo- 

 graphed by Rutherfurd. Six of the plates were carefully measured 

 under his direction with his improved micrometric apparatus pro- 

 vided with a glass scale for measuring the distances. The method 

 of measurement was precisely the same as that employed in the case 

 of the Pleiades plates, taken in 1872 and 1874,* and but very few 

 changes have been made in the method of reduction. The dates 

 and other particulars connected with the several plates are collected 

 in table I., at the end of the present paper. This table is similar to 

 the one given")" in my paper on the Pleiades, to which reference has 

 just been made. The measures of distance have all been corrected 

 for division errors, using the corrections determined by Professor 

 Rogers for the Rutherfurd scale. J No corrections for runs have 

 been applied, as the microscope used for reading the scale was 

 always kept very accurately adjusted. § 



The measures of the Eastern and Western impressions upon the 

 several plates have not been separately reduced, as in the case of 

 the Pleiades reductions. It has been quite sufficient to take the 

 means of the measures of the two impressions, and proceed with 

 them as a single observation. Thus the computations are shortened, 

 without becoming practically less rigid. Accordingly, the correc- 

 tions for refraction given in table II., are the means of the refrac- 

 tions computed for the Eastern and Western impressions, with the 

 data of table I. The refraction tables are similar in form to those 

 used in the reduction of the Pleiades. || 



* The Rutherfurd Photographic Measures of the Group of the Pleiades. 

 Annals N. Y. Acad, of Sciences, vi, 1892, Feb. 



f Ann. N. Y. Acad, vi, p. 241. \ Ibid., p. 250. 



§ Ibid., p. 251. I Ibid., p. 260. 



Annals N. Y. Acad. Sol, VI, May, 1892.-23 



