NEW POSITIONS OF STABS IN ORION 87 



having placed at my disposal the 26-inch refractor of the Leander 

 McCormick Observatory, it seemed desirable to 'apply direct micrometrical 

 measurements to these stars in the Huyghenian region in sufficient numbers 

 to obtain fairly accurate results. It further seemed probable : 1, that some 

 of the brighter stars, the former positions of which ought to be fairly 

 accurate, might in fifty or more years show some proper motion indepen- 

 dent of that of the trapezium ; 2, that, during the same period of time, new 

 variable stars might have appeared; 3, that some stars fainter than those 

 catalogued by Professor Bond might be seen with a telescope of larger 

 aperture. 



The observations were begun in September, 1908, and cover a period of 

 eighteen months. All the observations were made in position-angle and 

 distance. With the view to decreasing the errors arising from the measure- 

 ment of long distances, I adopted as fundamental stars 628 (0 Orionis) and 

 558, 669, and 685, stars forming a triangle about 628: These numbers are 

 the numbers of the stars in Bond's catalogue [H. C. 0. Annals, Vol. V], 

 and his designations are used throughout this paper, except in the cases 

 of stars which he did not catalogue. The position-angle of all six possible 

 combinations of the fundamental stars were measured on forty nights. The 

 measures of distances of the same combinations would average about 

 three less. From the average of the observed position-angles and distances, 

 differences in right ascension and declination were determined, and from 

 these the final differential positions with reference to 628 were determined 

 by a least square solution. The positions of the stars within 100" of the 

 trapezium were determined by measures with reference to 628 directly. 

 The positions of all stars outside of this central group were measured with 

 reference to the nearest fundamental star and through it referred to 628. 

 In some cases exceptions were made to this plan and two sets of measures 

 were made, one with reference to the nearest fundamental star, the other 

 with reference to 628 direct. In such cases both sets have been reduced 

 to differences in right ascension and declination. The first set has then 

 been referred to 628 by means of the definitive position of the fundamental 

 star and the two sets have then been combined, giving each observation 

 equal weight, to form the final position relative to 628. As far as practi- 

 cable, measures of position-angle and distance were made on ten nights for 

 each star. This plan has been carried out on all but five of the Bond stars 

 and none of these five, save 625, has been observed on less than seven nights. 

 See note on 625 in Part VI. 



