MOUNT WILSON OBSERVATORY. 269 



(7) Marked differences are shown in the radial velocities given by 

 the dark and bright lines of the Cepheid variable W Virginis. 



(8) Radial velocities have now been determined by Mr. Merrill for 

 101 long-period variables. Of these, 91 have spectra similar to that 

 of o Ceti, while the remaining 10 are classed as peculiar. 



(9) A least-squares solution by Mr. Merrill for the solar motion from 

 the bright lines of 83 variables of the Md (o Ceti) type yields the values 

 V= — 56km.,A = 274°,D = +44°. The average residual radial velocity 

 is 31 km., the greatest motion so far observed for a group of stars 

 selected on the basis of spectral tj^^e. The high value of the solar 

 motion is in agreement with the result found from statistical investi- 

 gations by Adams, Joy, and Stromberg, that stars of high velocity 

 have a strong preferential motion in a direction nearly opposite to 

 that of the sun. 



(10) The radial velocities of 28 stars of type R have now been 

 determined by Mr. Sanford. The velocities show the extraordinarily 

 high dispersion of from —400 to +70 km. The algebraic mean when 

 freed from the effect of the solar motion is —17 km. and the numeri- 

 cal mean is 50 km. 



Spectroscopic Determinations of Luminosity and Parallax. 



The absolute magnitudes and parallaxes of 1,646 stars derived by 

 the spectroscopic method are contained in Contribution No. 199, pub- 

 lished by the Observatory in January 1921. The contents of this 

 paper may be summarized as follows: 



1. Derivation of the reduction tables with the aid of trigonometric parallaxes, paral- 



lactic motion, and peculiar motion. 



2. Illustrations of the use of the reduction tables. 



3. Derivation of the probable errors. These are found to be of the order of ±0.4 



in the absolute magnitude and about 20 per cent in the parallaxes themselves. 



4. Comparisons with trigonometric parallaxes and with spectroscopic parallaxes derived 



previouslj\ 



5. Methods employed in the determination of the relative intensities of the lines used 



for the various types of spectra. 



6. Catalogue of the results for 1,646 stars. 



The spectroscopic method of determining absolute magnitude has 

 now been applied to about 350 stars in addition to those for which 

 results have been published, so that a total of 2,000 parallaxes derived 

 in this way is now available. 



One of the most direct applications of these results is to the giant 

 and dwarf theory of stellar development. If the stars are divided 

 according to spectral type and the numbers of stars of each absolute 

 magnitude are counted it is found at once that the A and F type stars 

 (excluding the Cepheids and pseudo-Cepheids) show a single maxi- 

 mum of frequency, the former around absolute magnitude +2, the 

 latter around +3.5. The G and KO to K 3 stars show two maxima, 

 the first at +0.5 and +5.5, the second at +0.5 and +6.2, with com- 



