Apeil 12, 1907] 



SCIENCE 



5B3 



distribution curve of these pairs closely re- 

 sembles that of the stars to 9.0 magnitude 

 in the same area, but that the double stars 

 are relatively more numerous in the richer 

 sky areas. 



When only the pairs under 2", or those 

 under 1", or the very close pairs, or the 

 brighter pairs, are considered, the same 

 relation is found; as may be seen from the 

 following table which groups the results by 

 quadrants : 



Table 

 Zone + 60° to + 90° 



Zone + 56° to + 60° 



Under 5' 



; 1:14.4 35 1:20.4 30 1:22.4 81 1:18.0 



The zones north of 60° were examined 

 with the 12-ineh telescope, but for fully 

 one half of the zone + 56° to + 60° the 

 36-inch was used. In this zone 4,257 stars 

 9.0 magnitude or brighter were examined 

 and 130 new double stars were added to 

 the 114 previously known pairs, giving a 

 ratio of one double star to 17.4 stars to 

 9.0 magnitude. The table shows that the 

 relations established in the area north of 

 60° hold true here also, though the ratio in 

 the fourth quadrant is affected by the fact 

 that in this quadrant the work was all done 

 with the 12-inch telescope. It is, therefore, 

 safe to state that in this entire sky area the 

 double stars are relatively as well as abso- 

 lutely most numerous in the region richest 

 in stars to 9.0 magnitude, that is, in the 

 region of the Milky Way. The study of 

 the local irregularities in the distribution, 

 of which the charts give evidence, is re- 

 served for a later paper. 



The Variable BS Persei: Ida Whiteside. 



Three minima of this star observed this 

 fall indicated a period of a little over 

 thirty-one days, through about two thirds 

 of which the star remained constant or 

 very nearly so. This period also agreed 

 very well with some scattered observations 

 published in the Astronomische Nach- 

 richten, and with others made at the 

 Vassar College observatory. At the time 

 predicted for the fourth minimum the star 

 failed to respond, going down very little if 

 at all. It is probably irregular, but more 

 observations are needed to confirm this 

 statement. The range is only about a 

 magnitude, from 8.2 to 9.2. 



A Systematic Error in Distance Measures 

 of Close Double Stars: W. H. Pickering. 

 In 1900 a series of measures was made 

 of the wide double star /x Draconis. Its 

 components are nearly equal, and their dis- 

 tance is 2". 3. The observations were ex- 

 ecuted with a 5-inch telescope whose aper- 

 ture could be reduced by a series of dia- 

 phragms to 0.5 inch. A magnification of 

 300 was usually employed. It was found 

 when the aperture was so small that the 

 disks of the two components were in con- 

 tact, or nearly so, that the distance between 

 their centers was materially reduced. With 

 an aperture of 0.6-inch the two centers 

 coincided. Had they remained at their 

 true distance apart, their combined image 

 would have been appreciably elongated, 

 instead of which it was perfectly circular. 

 It occurred to the writer to determine if 

 the same effect was produced in the case 

 of close double stars where large apertures 

 were employed. A selection of suitable 

 eases was made from Lewis's recent publi- 

 cation of measures of the Struve stars. It 

 was found that the apertures employed by 

 the various observers could be divided into 

 three classes, those of about 8 inches, those 

 of 15 inches and those of about 30 inches. 



