MOUNT WILSON OBSERVATORY. 209 



components is visible and appears to be of about type F8. The lines, 

 however, are extraordinarily wide and diffuse. The maximum relative 

 velocity of the two stars is about 330 km. 



4. The Algol variable TT Aurigae shows a range of velocity for the 

 principal component of over 400 km. 



5. Measurements of spectra of three of the cluster-type variables, 

 made in conjunction with Mr. Shapley, show exceptionally high radial 

 velocities for stars of this spectral type. The two stars SU Draconis 

 and SW Draconis have radial velocities of — 193 km. and — 74 km., 

 respectively, at maximum of light. RS Bootis has a velocity of — 51 

 km. at a similar phase. 



6. Observations of the Algol variable Boss 1646, recently discovered 

 by Schwab, show the presence of two spectra of closely the same type. 

 The relative velocity of the two components at maximum is 240 km. 

 The period is 2.52 days, or double that first announced from the 

 photometric observations. 



Determination of Solar and Stream Motion. 



An extended investigation of stars of the more advanced spectral 

 types has been carried out during the year by Mr. Stromberg relat- 

 ing to the correlation between absolute magnitude, on the one hand, 

 and radial velocity, the solar motion, and stream motion on the other. 

 Some of the main results may be summarized as follows : 



1. There is a steady increase in average radial velocity with 

 decreasing absolute brightness, a result in confirmation of that described 

 in the report of the previous year. 



2. The K term appears to be positive for the giant stars and negative 

 for the dwarf stars. 



3. The following values of the constants of the solar motion have 

 been derived from an investigation of the velocities of 1,405 stars of 

 advanced spectral types : 



A = 270?9±3?3 D=-i-29?2±3.4 Vo = 21.5 ±1.0 km. 



The constants are independent of the absolute magnitudes of the 

 stars employed. 



4. An appreciable asymmetrical distribution of the average radial 

 velocities has been found, indicating that the directions of maximum 

 velocity do not lie in exactly opposite directions, but are inclined to 

 one another by amounts which depend upon the distances of the stars 

 involved. 



5. The tentative suggestion is made that the properties of the 

 surface representing the average radial velocities may be explained on 

 the assumption that the stars are moving mainly around the center 

 of the galactic system, with a preferential motion in the galactic plane. 



Spectroscopic Determinations of Luminosity and Parallax. 



The absolute magnitudes of several hundred stars with spectral 

 types between A5 and M have been determined during the year. 



