MOUNT WILSON OBSERVATORY. 265 



for the mean value oim—M, with an average deviation of ±0.3 mag, 

 for individual stars. The corresponding mean parallax is 0''008. 

 The obscuring material can scarcely be nearer, and probably is not 

 more than three or four times the distance indicated by this value. 

 A possible exception to the statement that stars in obscured areas 

 do not show mu3h, if any, excess of color occurs among the faint stars 

 near o Persei, which are in a region of marked obscuration. The de- 

 tails are discussed in connection with nebulous stars on page 255. 

 Here it need only be remarked that the certain instances of excess 

 color thus far found anywhere are those of stars surrounded by lumi- 

 nous nebulosity. Although o Persei is in an obscured region, it is 

 near the nebula I. C. 1985, which involves nearly all, if not all, of the 

 objects showing an excess of color. 



Star Clusters and the Galactic System. 



The investigation of the star clusters and their bearing on the struc- 

 ture of the Galaxy has been continued by Mr. Shapley as in the past, 

 a large number of plates having been made with the reflecting tele- 

 scopes for both photometric and spectroscopic studies. Slitless spec- 

 trograms of globular clusters have confirmed the earlier conclusion 

 that the brightest stars are giants. 



The distribution of stars and the character of the variables in the 

 condensed type of globular cluster have been examined in order to 

 determine the distances more accurately and to find in what impor- 

 tant respect these few objects differ from typical globular systems. 

 An examination of many thousands of the fainter stars in the bright- 

 est globular clusters has been made by Miss Mayberry without find- 

 ing any conspicuous cases of variation. 



The distance of N. G. C. 7006 has again been determined, this time 

 by means of its newly discovered variable stars; the earlier value of 

 220,000 light-years is confirmed, with much higher weight than was 

 possible before. The dimensions of this most distant cluster and of the 

 relatively near cluster M 13 are essentially the same. 



The distribution of the stars with respect to the plane of the local 

 cluster and the galactic plane has been further investigated with the 

 aid of the data contained in the unpublished volumes of the Henry 

 Draper Catalogue. The brighter stars of spectral type B show clearly 

 the phenomenon of a secondary Milky Way; the famter B stars, how- 

 ever, show a symmetrical distribution with respect to the plane of the 

 Galaxy and evidently are not members of the star-cloud immediately 

 surrounding the sun. 



Variable Stars. 



A contribution to the problem of the velocity of light is made by 

 Mr. Shapley' s comparative study in blue and yellow light of the vari- 

 able stars in M 5 ; the investigation is still in progress. The close coin- 

 cidence of the maxima of the cluster-type variables for different colors 



