266 CARNEGIE INSTITUTION OF WASHINGTON. 



with the appHcation of the final zero-point correction, the outstanding 

 difference between the sixth and tenth magnitudes, which originally 

 was about 0.4 mag., has been decreased to 0.24 mag. 



In an effort to locate the source of this remaining difference, the 

 Harvard data relating to the stars brighter than the tenth magnitude 

 were re-reduced wherever possible by methods which did not involve 

 the direct use of the reduction constants of the screens and diaphragms 

 with which the photographs were made. This was accomplished by 

 assuming the vaUdity of the scale between the tenth and fifteenth mag- 

 nitudes and transferring the same to the region of the brighter stars. 

 In this manner the agreement of the Harvard and Mount Wilson results 

 was extended from the tenth upward to the eighth magnitude. The 

 remaining discordance of about a quarter of a magnitude is thus tlirown 

 upon the stars between the sixth and the eighth magnitudes. 



Magnitudes for the Selected Areas. 



In this investigation, which is in the hands of Mr. Seares, about 

 three-fourths of the diaphragm plates necessary for the determination 

 of the scales of the individual areas have been obtained. In the 

 meantime, the intercomparison of the areas with each other and with 

 the pole for the derivation of the zero-point corrections has been begun. 

 About 80 plates for this part of the investigation have been obtained. 

 The reductions have progressed satisfactorily, although the large 

 number of stars registered in some of the richer fields makes the work 

 slow. 176 plates have been completely measured; 15 plates have been 

 measured once. For 34 areas the measures are complete, while for 

 24 others one-half of the work is finished. The reductions, up to and 

 including the relative magnitudes, are complete for 22 areas. Although 

 these are mainly in the intermediate or higher galactic latitudes, the 

 fields (diameter 23', exposure 15 minutes) show an average of 125 

 stars per area. It is of interest further to note that 4 areas near the 

 Milky Way (mean galactic latitude = 4°) show an average of 1,400 

 stars per field. 



Magnitudes and Colors in Clusters. 



The completion of the derivation of standard magnitude scales per- 

 mits the application of photometry to the determination of the colors 

 of faint stars in special regions of the sky. A systematic investigation 

 of the photographic and photovisual magnitudes in open and globular 

 clusters has been begim by Mr. Shapley and nearly a dozen clusters 

 have been compared with the North Polar Standards. The measure- 

 ment and reduction of the plates is well under way, and a catalogue of 

 the magnitudes and colors of 1,302 stars in Messier 13 has been com- 

 pleted. The results obtained bear directly on such questions as the 

 distance of globular clusters, the relation of color to absolute magni- 

 tude, the absorption of light in space, and the absorption peculiar to 



