MOUNT WILSON SOLAR OBSERVATORY. 261 



Besides the redetermination of secondary standards and the addition 

 of new Unes to the Hst of secondaries, work in progress includes a com- 

 parison of wave-lengths of selected hnes taken from the 220-volt arc 

 recommended by the International Conmiittee with those taken from 

 the Pfund arc at 110 volts and also from an arc having one terminal 

 of carbon. Our program includes the evaluation of wave-lengths ob- 

 tained from the iron arc in vacuo, both by direct comparison with the 

 red cadmium line and by reference to the spectrum of the arc under 

 normal pressure. The iron hnes from the vacuum arc are extremely 

 sharp and large numbers of them can easily be obtained with intensity 

 sufficient to serve as secondary standards. 



COMPUTING DIVISION. 



The Computing Division has remained throughout the year under 

 the direction of Mr. Seares. 



For some weeks Miss Brayton was engaged with the reductions of a 

 group of 34 photometric plates for the Selected Areas, but latterly 

 has been occupied exclusively with the work in stellar spectroscopy. 

 She has measured and completely reduced 391 spectrograms and has 

 done miscellaneous checking and work on the preparation of reduction 

 tables for spectrograms. 



Miss Carolyn Burns has continued her work in stellar photometry. 

 76 Selected Area plates have been measured and reduced, and miscel- 

 laneous reductions relating to other plates have been finished. 



Miss Margherita Burns joined the Division on January 1 and has 

 devoted her time to the work of the physical laboratory. The screws 

 of three measuring machines have been tested, measures and reductions 

 relating to 17 Zeeman plates have been made, and much miscellaneous 

 work connected with the interferometer observations by Mr. Babcock 

 has been done. 



Miss Burwell still gives the greater part of her time to the study of 

 stellar spectrograms, 470 plates having been measured during the year. 

 An extended series of estimates of line-intensity for the determination 

 of spectral type and absolute magnitude has also been made. 



Miss Davis has spent half of the time upon the photometric investiga- 

 tions of Mr. Shapley. She has measured about 125 photographs of 

 variables and clusters and has reduced 40 others, besides plotting 

 extended series of observations on several of the cluster-type variables. 

 Her remaining time has been given to the parallax and proper motion 

 work of Mr. van Maanen. Least-squares solutions were affected for 

 15 parallax fields and assistance was given in the reductions for deter- 

 mining the internal motions of M 81 and M 101. 



Mrs. Fretter continued to assist with the work of the physical 

 laboratory until the date of her resignation on January 1. 



