1894.] 



Photographic Spectrum of y- Cassiopeia. 



175 



Stars."* A complete list of the photographs is given in the follow- 

 ing table. 



Results of the Preliminary Discussion. 



(1) .4ZZ ^e photographs taken at Kensington show "bright lines of 

 hydrogen. 



The lines H/3, H7, and H are constantly seen, and He and H^ 

 appear when the photographic conditions have been good. This 

 suggests that their apparent absence, noted by some observers in the 

 period 1874 to 1883, was possibly due to imperfect conditions of 

 observation. - 



(2) In addition to the bright lines of hydrogen, there are other bright 

 lines in the spectrum. 



The additional bright lines appear in all good negatives ; in cases 

 of under or over exposure, or when other conditions have affected the 

 quality of the negative, they are not distinctly seen. 



For the most part, these lines are ill-defined ; their positions, there- 

 fore, cannot be determined with any great degree of accuracy. 



* ' Phil. Trans.,' A, 1893, vol. 184, p. 678. 



