228 CARNEGIE INSTITUTION OF WASHINGTON. 



bination of his photographic magnitudes with those of Kapteyn and 

 van Rhijn, made with the assistance of Miss Joyner and Miss Rich- 

 mond, are practically complete for areas 1 to 67 (p. 261) . Mr. Shapley, 

 assisted by Miss Richmond, has finished a survey of the photographic 

 and photovisual magnitudes of about 850 stars in the Pleiades between 

 magnitudes 10 and 15.5. Within this range the members of the clus- 

 ter are dwarfs of absolute magnitude 5 to 10.5 (p. 261) . In connection 

 with the work of the International Committee on Magnitudes, Mr. 

 Scares, as chairman, has made a series of tests of the Mount Wilson 

 photometric scale. These confirm earlier tests and show perfect agree- 

 ment with Hertzsprung's measures for the interval between magnitudes 

 6 and 13 (p. 262). A study of the colors of 60 stars in the Pleiades by 

 Mr. Scares has afforded a useful check on the method of reduction 

 and confirmed two anomalous results suspected from other evidence 

 (p. 263). 



Reference has already been made to Mr. Seares's investigations of 

 stars in the Galaxy. From these he has derived provisional estimates 

 for the distance of the galactic clouds, which range from 20,000 to 

 50,000 light-years for the blue stars of apparent magnitude 14 to 15.5. 

 These are minimum values, indicating a scale for our stellar system in 

 harmony wi^h that derived by Mr. Shapley from his studies of globular 

 clusters (p. 263). 



Mr. Shapley has continued his work on globular clusters and related 

 problems. The distance of the cluster N. G. C. 7006, previously found 

 to be 220,000 light-years, has been confirmed by a study of its variable 

 stars (p. 265). He has also extended his investigation of the distribu- 

 tion of the stars with reference to the plane of the local cluster and the 

 galactic plane, and finds that the brighter B stars belong to the star- 

 cloud immediately surrounding the sun, while the fainter B stars do 

 not (p. 263). 



A relationship discovered by Mr. Shapley between the light-curves 

 of Nova? and certain irregular variable stars suggests that the outburst 

 and variation of Nov2e may result from causes such as are active in 

 these variables (p. 265). He has also examined the question whether 

 the changes m geological climates may be due to causes analogous to 

 those that produce the ii-regular Orion variables, where motion through 

 nebulosity seems to be the source of variation (p. 266). The eclipsing 

 binary SX Cassiopeise, studied in association with Mrs. Shapley, is of 

 exceptional interest, because its mean density is of the order of 0.0005 

 that of the sun. This system actually consists of a very close pair of 

 giant stars, each having a linear diameter comparable with that of 

 Arcturus (p. 266). 



The faintest and most distant known variables are 19th magnitude 

 stars in the globulai cluster N. G. C. 7006. From an investigation by 

 Mr. Shapley and Miss Mayberry, these objects appear to be typical 



