270 CARNEGIE INSTITUTION OF WASHINGTON. 



With the aid of stars having a common radial velocity, an improved 

 proper motion of the double cluster h and x Persei has been derived. 



The plates for photographic magnitudes in the Selected Areas are 

 8G per cent complete, and relative magnitudes have been determined 

 for 70 of the 115 regions. Observations for photo visual magnitudes in 

 37 of the areas have been begun. 



It is found that the ratio of the exposure-times necessary for the blue 

 and yellow light of a star to produce images of the same size is a 

 reliable measure of the star's color. The precision is sufficient to reveal 

 the influence of abnormal luminosity upon color. 



Color photographs of certain spiral nebulae show that their central 

 nuclei are yellow, while the branches are very blue. 



A continuation of the investigation of magnitudes and colors in 

 clusters confirms the presence of giant red stars in the globular clusters 

 and the neghgible value of light-scattering in the direction of the 

 Hercules cluster. Catalogues of magnitudes and colors for this cluster 

 and for Messier 67 have been completed. 



The study of magnitude and color changes of variable stars has been 

 continued, notably for the variables in Messier 3, and for XZ Cygni 

 and TW Andromeda?. Variations in the elements of U Cephei have 

 been investigated and the orbits of several eclipsing stars have been 

 calculated. 



The radial velocities of 141 stars have been determined from three or 

 more spectrum photographs. Five stars show velocities exceeding 100 

 km.; one with a velocity of —250 km. is of type A9. 



The cluster variable XZ Cygni has a motion of about — 150km., with a 

 moderate variation of velocity. Its spectrum varies from about A2 at 

 maximum of Hght to A8 at minimum. 



The star Boss 46 is a spectroscopic binary of type B3 with double 

 lines. The maximum relative velocity so far observed is about 400 km. 

 The H and K lines show little or no variation, but the orbit is still under 

 investigation. The period appears to be of the order of two days. 



The spectrum of Barnard's large proper-motion star is Mb and it 

 belongs to the dwarf class of M stars, with the spectral characteris- 

 tics peculiar to this class. Its radial velocity is about —94 km. 



An investigation of the spectral relationships between stars of 

 difi'erent absolute magnitudes has been published, and a method has 

 been derived for obtaining parallaxes from spectral peculiarities. An 

 application to 124 stars of measured parallax gives values in satis- 

 factory agreement with measured results, the average deviation from 

 the latter being 0''025, with distinctly better agreement for parallaxes 

 of highest weight. The method apparently may be applied both to 

 stars of high and low absolute luminositj^, and hence to the determina- 

 tion of very small parallaxes. It seems to be most accurate in the case 

 of the K and M-type stars, and least for the F stars. 



