1894.] 



Photographic Spectrum of 7- Cassiopeice. 



Ill 



(8) Besides the dark bands in the positions of the hydrogen lines, there 

 are other ill-defined dark lines. 



The additional dark lines are seen in all good negatives, whether 

 taken with high or low dispersion, but their haziness makes their 

 positions difficult to determine with accuracy. The approximate 

 wave-lengths of the principal dark lines are 3887, 3968, 3994, 4008, 

 4025, 4069, 4101, 4119, 4143, 4168, 4340, 4388, 4471, 4643, 4860. 

 This at once contradicts Professor Scheiner's recent statement* that 

 he " does not believe- it possible that dark lines can exist in the 

 spectrum." 



(9) The dark lines in the spectrum of ^-Cassiopeice correspond very 

 closely with the lines seen in the spectra of "- and 7- Orionis. 



This fact was recognised at an early stage of the inquiry, and the 

 similarity is shown by the accompanying enlargements. The resem- 

 blance is further shown by the appended table, the wave-lengths of 

 the lines in the spectra of - and <y-0rionis being taken from a former 

 communication. f 



The numbers following the wave-lengths refer to the estimated 

 intensities of the lines, 6 representing the strongest lines. 



The photographs have been taken at different times by Messrs. 

 Fowler, Baxandall, Shackleton, North, Fournier, and Butler. 



Mr. Fowler has also assisted in the preparation of the present pre- 

 liminary communication. 



* ' Astronomical Spectroscopy,' Frost's translation, 1894, p. viii. 

 f ' Phil. Trans./ vol. 184, A, pp. 693, 695. 



VOL. LVII. 



