268 CARNEGIE INSTITUTION OF WASHINGTON. 



The values of the absolute luminosities obtained in this way proved 

 to be in satisfactory agreement with those computed from parallax or 

 proper motion. The average differences for the 71 Fg to Ge stars is 

 about 1.6 magnitudes; for the 91 Ge to Kg stars slightly less than 1.5 

 magnitudes. It appears, therefore, that the use of spectral lines as 

 criteria for the determination of absolute magnitude and parallax 

 promises valuable results in this difficult field of investigation. 



Spectra of Temporary Stars. 



Spectra of the following temporary stars have been obtained during 

 the year by Mr. Adams and Mr. Pease with the small spectrograph at 

 the primary focus of the 60-inch reflector : 



Nova Aurigae 1891 Mag. 14 



Nova Persei 1901 12.4 



Nova Lacertse 1910 12.5 



Nova Geminorum No. 2 1912 10 



Nova Geminorum No. 2 has also been photographed with the 

 Cassegrain spectrograph. The exposures ranged from 2 to 16 hours. 

 An examination of the spectra leads to the following conclusions: 



The principal nebular lines at X 4959 and X 5007 have disappeared 

 from the spectra of Nova Aurigse and Nova Persei, but are still present 

 in the other two stars. This observation is in agreement with that of 

 Hartmann in 1907 on Nova Persei. The continuous spectrum is very 

 strong in Nova Aurigse and Nova Persei, less so in Nova Lacertse, and 

 of variable intensity in Nova Geminorum No. 2. The principal nebular 

 line at X 5007 is intensely strong in Nova Lacertse, but the nebular line 

 at X 4364 usually ascribed to the same vibrating atom is very weak. 



The disappearance of the chief nebular lines in the spectra of the 

 older of these stars makes them identical with the spectra of some of 

 the Wolf-Rayet stars. In view of this fact and the well-known agree- 

 ment in distribution relative to the Milky Way of Novse and Wolf- 

 Rayet stars, it seems probable that at least a portion of the latter are 

 temporary stars in the later stages of their histor3^ 



Since there is at present no hypothesis which accounts for the phe- 

 nomena of a temporary star in a more satisfactory way than by the 

 entrance of the star into a nebula, the possibility may be suggested 

 that the disappearance of the chief nebular lines may coincide with the 

 emergence of the star from the nebula. 



Spectra of Stars in the Hercules Cluster M 13. 



Mr. Pease has obtained an additional photograph of this cluster 

 with the focal plane spectrograph, using a slit-width of 0.050 mm. and 

 an exposure of 30 hours. 



The slit was set S" south of the star Scheiner 373, which Barnard 

 uses as his normal star, and stars are scattered over a distance of 



