214 CARNEGIE INSTITUTION OF WASHINGTON. 



Stellar Photometry. 

 The observational part of the investigations in stellar photometry 

 by Mr. Seares includes 455 photographs, all made with the 60-inch 

 reflector and distributed as follows: RR Draconis, 16; brighter stars 

 of the North Polar Sequence, 175; Selected Areas, 199; miscellaneous, 

 65. The last group includes, among others, plates taken at the request 

 of Professor Pickering, Professor Charlier, and Dr. Schlesinger. 



RR DRACONIS. 



The photographs of the Algol variable RR Draconis were made in 

 part with color-sensitive plates and a yellow filter adjusted to give 

 approyimately visual magnitudes. The comparison of these "photo- 

 visual" results with the ordinary photographic magnitudes shows an 

 increase in the color index as the variable approaches its minimum. 

 During minimum the index exceeds that corresponding to normal 

 light by 0.57 mag. The light of the faint star is only 3 per cent of the 

 total radiated, and since the eclipse is total, the change in color is 

 a measure of the difference in the spectral types of the two com- 

 ponents, the probable values being A 2 and F5, respectively. The 

 increase in redness as the minimum is approached is in agreement 

 with what would be expected from the fact that the fainter object is 

 much the larger of the two, but raises an interesting question as to the 

 relation between spectrum and density. Although the darker star is 

 the larger, its density is probably less than that of the bright object. If 

 the ordinary relations between spectrum and color index apply, we 

 have apparently an advanced spectrum associated with a relatively 

 low density. 



NORTH POLAR SEQUENCE. 



The observations are a continuation of those previously reported, 

 and are concerned with the determination of the photographic scale 

 for the stars brighter than magnitude 10.5. The magnitudes pre- 

 viously found for the objects between 10.5 and 15.5 are in excellent 

 agreement with the results derived at the Harvard Observatory. 

 The scale for this region was accordingly assumed to be accurately 

 known, and the further observations were arranged in such a way as 

 to establish for the bright stars a scale which should be homogeneous 

 with that assumed as the basis of the investigation. Each bright 

 star was photographed upon the same plate with a group of faint 

 stars, the full aperture of 60 inches being used for the latter, and for 

 the former, diaphragms and screens producing an apparent bright- 

 ness falling within the Hmits of the adopted scale. The subtraction 

 of the reduction constant of the diaphragm or screen from the 

 observed apparent magnitude gave the required magnitude of the 

 bright star. All magnitudes determined with the same diaphragm or 

 screen are affected equally by the error in the reduction constant, 

 and hence the scale should be homogeneous with that adopted for the 



