MOUNT WILSON OBSERVATORY. 241 



The absolute magnitudes and masses were determined for 37 visual 

 binaries, for which both the orbits and the parallaxes are kno^vn with at 

 least fair accuracy. The results show clearly a relationship between 

 mass and absolute magnitude. 



STELLAR PHOTOMETRY. 



The observational part of the investigations in stellar photometry 

 by Mr. Seares and Mr. Shapley includes 465 photographs, all made 

 with the 60-inch reflector and distributed as follows: Selected Areas, 

 113; clusters, 175; color photographs of stars, 125; miscellaneous, 52. 



Photographic Magnitudes for the Selected Areas. 



The observational program was finished by Mr. Seares early in the 

 year. Final magnitudes based on a normal scale and referred to the 

 international zero-point are now available for Areas 1 to 91. The 

 relative magnitudes for Areas 92 and 139 are complete. With the 

 exception of 6 plates, the intercomparison photographs for the latter 

 group of areas have been completely measured and reduced. The 

 correction of the relative magnitudes for zero-point can therefore be 

 undertaken almost immediately. The addition of the reduction con- 

 stants will complete the photometric part of the program for the photo- 

 graphic magnitudes. Coordinates sufficient for purposes of identifi- 

 cation of the stars are already in process of determination. Results 

 for Areas 1 to 22 are available at present. 



Miss Joyner and Miss Richmond have given the greater part of their 

 time to the measures and reductions connected with this investigation. 



Photovisual Magnitudes for the Selected Areas. 



This investigation, as outlined in previous reports, has been con- 

 tinued by Mr. Seares and Mr. Shapley, and 159 of the 257 photographs 

 required have now been obtained. The measures of the plates are 

 nearly complete to date. 



Relation of the Color of Stars to their Intrinsic Brightness. 



The measurement of the color of stars by the method of exposure 

 ratios has been continued by Mr. Seares for the purpose of determining 

 the relation of color to intrinsic brightness in objects of the same 

 spectral class. The faintness of the violet end of the spectrum of the 

 giant stars of the later types has been known for some years. The 

 observations confirm this result for the G and K stars, and afford a 

 quantitative determination of the dependence of color upon absolute 

 magnitude. The M stars, however, seem to have nearly the same 

 color, whatever their luminosity. 



Preliminary results for B, A, and F stars have also been obtained. 

 The very luminous B's seem to be redder than those somewhat fainter. 



