228 CARNEGIE INSTITUTION OF WASHINGTON. 



Father Luis Rodes spent the greater part of the year as a volunteer 

 assistant at the Observatory, returning to Spain in July. From Octo- 

 ber 1 to May 1 he assisted in the photographic work with the 60-foot 

 tower telescope. Mr. Toshio Takamine, of the University of Tokyo, 

 spent the period September 1918 to April 1919 as volunteer assistant 

 in the Physical Laboratory, where he conducted an investigation on 

 the effect of an electric field on metallic spectra. Dr. John C. Duncan, 

 director of the Whitin Observatory, Wellesley College, came to Mount 

 Wilson for stellar spectrographic work and the photography of nebulae 

 during the summer of 1919. Mrs. Harlow Shapley, volunteer assist- 

 ant, has continued to collaborate with Dr. Shapley in his stellar 

 investigations. Miss Edna Carter, associate professor of physics at 

 Vassar College, returned for the summer of 1919 as volunteer assistant 

 in the Physical Laboratory, where she has continued her studies of 

 metaUic spectra produced by the cathode discharge. 



Mr. L. B. Aldrich had charge of the work of the Smithsonian Astro- 

 physical Observatory on Mount Wilson during the summer of 1919. 



INVESTIGATIONS IN PROGRESS. 



SOLAR RESEARCH. 



The 30-foot vertical spectrograph, designed for use in conjunction 

 with the remodeled Snow telescope, has been completed and employed 

 for certain investigations mentioned in the present report. A new 

 form of measuring machine, involving the principle of the heliometer 

 and especially applicable to differential measurements of photographs 

 of the Zeeman effect in sun-spots, has been constructed after designs 

 by Mr. Anderson. 



SOLAR PHOTOGRAPHY. 



During the year ending August 31, 1919, the following solar photo- 

 graphs were taken with the 60-foot tower telescope by Messrs. Eller- 

 man, Nicholson, Rodes, Benioff, Henshaw, Brackett, and Baker: 



Photoholioejams of 6.5 image, 340 on 32.5 days. 



Spectroheliograms with 5-foot spectroheliograph {Ha, entire 6.5-inch disk), 191 on 191 days. 



Spectroheliograms with 13-foot spectroheHograph (K and Ha, 2-inch disk and prominences; 



Ha, portions of 6.5-inch disk, monochromatic Hght from continuous spectrum), 1,177. 



Photographs of spectra taken with the 75-foot spectrograph of the 

 150-foot tower include 102 exposures for solar rotation (Mr. St. John), 

 53 exposures for motion in sun-spots (Mr. St. John), and 40 for the 

 investigation of magnetic fields in sun-spots and at other points on the 

 disk (Mr. Ellerman, Mr. Nicholson, and Mr. Brackett). Some of 

 these photographs, made with the assistance of Mr. Merrill on plates 

 sensitized with dicyanin, kindly furnished us by the Bureau of Chemis- 

 try of the Department of Agriculture, extend our records of sun-spot 

 spectra into the infra-red as far as X7900. 



