240 



The Spectrum of y Cygni. 



" The Spectrum of 7 Cygni." By Sir Norman Lockyee, K.C.E , 

 F.R.S., and F. E. Baxandall, A.RC.Sc. Eeceived Decem- 

 ber 11— Bead December 11, 1902. 



(Abstract.) 



The paper gives an account of the investigation of the Spectrum 

 of 7 Cygni in relation to other celestial and terrestrial spectra. 

 It is pointed out that this spectrum — which is of the Polarian 

 type in the Kensington classification — is the connecting link between 

 the spectrum of the Aldebarian stars, in which the arc lines of the 

 metallic elements predominate, and that of a Cygni, chiefly com- 

 posed of the enhanced lines of some of the metals. These two sets 

 of lines are of about equal prominence in the 7 Cygni spectrum. 



It is also shown that, in regard to the relative intensities of the 

 metallic and proto-metallic lines, there is a close resemblance between 

 the spectrum of 7 Cygni and that of the chromosphere, thus indicating 

 that the temperature and electrical conditions prevailing in the two 

 light sources are nearly identical. A comparison, however, of the 

 intensities of the stronger arc and enhanced lines in the two spectra 

 tends to show that the chromosphere is, if anything, of a slightly 

 higher temperature. 



It is claimed that the majority of the lines of 7 Cygni — and therefore, 

 also, of the chromosphere — are due to metallic vapours, and that 

 there is little evidence to support Professor De war's suggestion 

 that most of the 339 chromospheric lines, recorded by Humphreys in 

 his eclipse results, can be accounted for as probably being due to the 

 rarer atmospheric gases. 



The relation of the 7 Cygni spectrum to that of a Cygni is also 

 discussed in detail. 



At the end of the paper a table is given showing the wave-lengths, 

 intensities, and probable origins of the lines which occur in the 

 photographic spectrum of 7 Cygni, taken with a 6" Henry prism of 

 45° angle. The lines are compared with those of the chromosphere, 

 S Canis Ma j oris (Pickering's record), and a Cygni. 



