MOUNT WILSON SOLAR OBSERVATORY. 205 



Miss Bray ton, have made measures and reductions relating to stellar 

 spectroscopy. Miss Richmond, Miss Joyner, Miss Carolyn Burns, 

 Miss Winn, and Miss Davis have been occupied with stellar photom- 

 etry, and Miss Richmond has assisted Mr. Pease and Dr. Shapley 

 with the discussion of an extensive series of counts on photographs of 

 clusters. For part of the year Miss Davis was also occupied with 

 reductions of parallax measures for Dr. van Maanen. Miss Wolfe has 

 given her time to reductions of stellar parallax and the sun's general 

 magnetic field. She has also done miscellaneous computing and photo- 

 graphic work, and has assisted in the hbrary. Miss Margherita Burns 

 and, for the latter part of the year. Miss Brayton, have been engaged 

 with the work of the Physical Laboratory. Miss Connor has con- 

 tinued as librarian and has assisted with the editorial work. 



Dr. J. van der Bilt served as a volunteer assistant on Mount Wilson 

 from September to January. Mrs. Harlow Shapley has continued her 

 service as a volunteer assistant in connection with the work in stellar 

 photometry. Miss Edna Carter, Associate Professor of Physics at 

 Vassar College, who began work last year as a volunteer assistant in 

 the physical laboratory, is still devoting her attention to metallic 

 spectra produced by the cathode discharge. Mr. Hugo Benioff has 

 served for two months as volunteer assistant on Mount Wilson. 



Mr. L. B. Aldrich has continued the work of the Smithsonian 

 Astrophysical Observatory on Mount Wilson during the summer of 

 1917. 



INVESTIGATIONS IN PROGRESS. 



SOLAR RESEARCH. 



Few changes have been made during the year in the equipment for 

 solar observations. The final details in the remodeling of the Snow 

 telescope and the installation of the new vertical spectrograph have 

 been delayed by the pressure of other work in the insti*ument shop, 

 but it is hoped that these important improvements may soon be 

 completed. 



A small but valuable addition to the 75-foot spectrograph consists 

 of a parallel-plate micrometer, mounted in the plate-holder support, 

 and serving for daily visual measures of the strength of the magnetic 

 fields in sun-spots. 



SOLAR PHOTOGRAPHY. 



During the year ending August 31, 1917, the following photographs 

 were taken with the 60-foot tower telescope by Messrs. Ellerman, 

 Nicholson, Joy, van der Bilt, Campbell, Whitney, and Benioff: photo- 

 hehograms of 6.5-inch image, 307 on 307 days; 5-foot spectroheliograms 

 (Ha, entire 6.5-inch disk), 298 on 298 days; 13-foot spectroheliograms 

 (K and Ha, 2-inch disk and prominences; Ha, portions of 6.5-inch disk), 

 1,248. 



