272 CARNEGIE INSTITUTION OF WASHINGTON. 



Space-Velocity and Absolute Magnitude. 



The determination of the distances and absolute magnitudes of stars 

 has made it possible, through combination with proper motion and 

 radial velocity, to derive space-motions and to study their relationship 

 to absolute magnitude. An investigation of this character, based 

 upon the results for the 1,646 stars to which reference has been made, 

 leads to results of considerable interest, 



1. The average space- velocities of stars of types F, G, K, and M 

 vary with absolute magnitude to a marked degree, the fainter stars 

 moving more rapidly than the brighter ones. The giant stars show 

 an especially regular increase of velocity with decreasing brightness. 

 The increase in average space-velocity is about 3 km. for a decrease 

 in brightness of one magnitude. 



2. The tangential and radial velocities show results in harmony 

 with the space- velocities. 



3. The average space-velocity of the giant stars is very nearly twice 

 the average radial velocity, a result which would follow strictly if 

 equal numbers of stars moved in all directions. 



4. The variation of velocity with spectral type is well marked among 

 the giant stars, but less certain among the dwarfs. The latter show a 

 very wide dispersion of motions and are much less homogeneous as a 

 class than the giants. 



5. The frequency of the space-velocities can not be represented by a 

 distribution according to Maxwell's law, there being a large excess of 

 high velocities. The assumption of a normal error-distribution of the 

 logarithms of the velocities instead of the velocities themselves satis- 

 fies the observations much better. 



Systematic Motions of Stars Based upon Space-Velocities. 



An extensive investigation by Mr. Stromberg of the systematic mo- 

 tions of stars with parallaxes derived by the spectroscopic method is 

 now in progress. Brief reference may be made to a few of the results. 



1. Solutions of the solar motions based separately upon 800 giant 

 stars and 415 dwarf stars give values for the velocity for the sun of 

 19.1 km. and 32.4 km., respectively. The difference is found to be 

 due to systematic motions on the part of the dwarf stars. 



2. A similar solution, using groups of stars divided according to the 

 amount of space-velocity, shows that the stars with space-velocities 

 between and 60 km. yield a value of the solar motion in close agree- 

 ment with that commonly adopted, V = 20 km., with the apex at 

 A = 270°, D=-|-30°. The stars with higher velocities give system- 

 atically larger values for A and D and a great increase in the apparent 

 value of V. 



3. The conclusion from these results is that the motions of the stars 

 with large velocities, the great majority of which are of the F type and 



