212 CARNEGIE INSTITUTION OF WASHINGTON. 



a number of the bright lines which appear in the spectrum near mini- 

 mum of light with Unes of iron belonging to the low-temperature 

 groups of a and h. It seems probable, therefore, that the atmosphere 

 of the star near minimum undergoes a fall in temperature which 

 favors the appearance of these lines, A similar behavior is found for 

 the magnesium line X 4571. This behavior may prove to be charac- 

 teristic of the other stars of the Md type. 



2. The spectra of the individual components of several visual 

 double stars have been investigated ; if the difference in magnitude is 

 not too great, it is possible, under favorable observing conditions, to 

 obtain results for stars separated by 1''5. In a large majority of cases 

 the fainter component has the more advanced type of spectrum and 

 frequently is of very low intrinsic brightness. It is evident, therefore, 

 that only in the case of relatively near stars would many of the systems 

 appear binary, the fainter component becoming invisible at great 

 distances on account of low absolute brightness. This may account 

 in part, at least, for the results found by Perrine, indicating a de- 

 pendence of spectral type of the components of double stars upon 

 distance. 



3. In continuation of the investigation of the effect of absolute 

 magnitude upon the intensity of the continuous spectrum in the 

 more and less refrangible portions of the spectrum, about 700 spectro- 

 grams have been compared by Mr. Sanford with suitable standard 

 photographs. The absolute magnitudes of nearly all of these stars 

 are available from spectroscopic determinations. 



SPECTROSCOPY OF NEBULA AND STAR-CLUSTERS, 



Investigations of the spectra of nebulae and star- clusters have been 

 carried on by Mr. Pease and Mr. Sanford with the small focal-place 

 spectrograph and the 60-inch reflector. Forty-one spectrograms have 

 been measured for radial velocity by Mr. Sanford, among them a 

 number of photographs of selected stars in clusters as well as of 

 spiral and gaseous nebulae. 



Observations both of radial velocity and of spectral type are of 

 especial interest in connection with star-clusters because of the investi- 

 gations by Mr. Shapley and others on the colors of the stars in objects 

 of this nature. As an illustration reference may be made to the star 

 hsted by Bailey as No. 95 in his list of variables in the globular cluster 

 Messier 3. A spectrogram made with an exposure time of 11 hours 

 indicates that its spectrum is of advanced type and contains bright 

 hydrogen lines. A large color-index has been found for this star by 

 Mr. Shapley, and Bailey has shown that it can not be included among 

 the numerous short-period variables of the cluster type. A second 

 spectrogram failed to show the bright lines. It is possible that the 

 star is a variable of tjrpe Md. 



