216 CARNEGIE INSTITUTION OF WASHINGTON. 



tion of the colors of the stars in the 30° zone. The photographs of shorter 

 exposure time are being supplemented by exposures of 64 minutes, which will 

 extend the determinations to stars of the seventeenth photovisual magnitude. 

 A detailed account of the methods and the results of many miscellaneous 

 observations are in preparation for publication. The results for a large num- 

 ber of stars of selected spectral types and absolute magnitudes will also be 

 published and should afford improved values of the numerical relationships 

 between color index, absolute magnitude, and spectral type. 



In the field of stellar spectroscopy, work is being continued on an extensive 

 list of stars which includes many stars of large proper motion, visual binaries, 

 variables of the cluster type and the fainter Cepheids, the brighter stars in the 

 Selected Areas, spectroscopic binaries, and most of the stars of Boss's Cata- 

 logue. For all of these, determinations both of radial velocity and absolute 

 magnitude are in progress. The revision and improvement of the present 

 methods for the determination of absolute magnitude through the use of 

 additional spectral criteria and results obtained from trigonometric parallaxes 

 and peculiar and parallactic motions forms an important feature of this work. 



Additional investigations in stellar spectroscopy include detailed physical 

 studies of types Me and S, helium stars with bright lines, stars of the a Cygni 

 type, and former novae. The brighter stars in globular clusters are being 

 observed for radial velocity and spectral type, and the classification of the 

 spectra of stars in the Selected Areas to the twelfth magnitude is a regular 

 part of the observational program. 



The application of the results of determinations of radial velocity and abso- 

 lute magnitude to studies of the distribution of the motions of stars in space 

 has led to important conclusions and is one of the principal objects of the work 

 in progress. Of especial interest in this connection is the investigation of 

 the space-velocities of the stars of types Me and R, both of which are char- 

 acterized by an exceptionally large dispersion in motion. 



Radiometric observations of stars and planets with a highly sensitive 

 thermo-couple are being continued regularly, and are yielding most valuable 

 information regarding the nature of the radiation and the physical conditions 

 in these bodies. 



LABORATORY RESEARCH. 



The use of the electric furnace for the production of spectra at relatively 

 low temperatures under conditions easily controlled, and the powerful 

 methods of wire explosions and vacuum sparks for very high temperatures, 

 form a most valuable means of attack upon problems relating to ionization 

 and series relationships in complex spectra. The classification of lines 

 according to their behavior in the electric furnace over a long range of 

 spectrum is providing a basis for the selection of groups of lines of similar 

 constitution separated by recurring intervals in their vibration-frequencies. 

 Such groups form the material for the determination of the series of lines 

 emitted by electrons at different energy levels. 



Of equal importance for investigations of this character is the detailed 

 study of the Zeeman effect and the measurement of the separations of the 

 components of the spectral lines in a magnetic field. A strong incentive to 

 further work is provided by the remarkably successful application of the 

 quantum theory to the interpretation of complicated spectra. 



