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Vn. The Spectrum of y Cygni. 
By Sir Normax Lockyer, K.C.B., F.R.S., and F. E. Baxaxdall, A.R.C.Sc. 
Keceived December 3,—Read December 11, 1902. 
[Plate 1.] 
In a paper on “ The Chemical Classification of the Stars,” communicated to tlie Koyal 
Society on May 4, 1899,"'^ one of us indicated that it was then possible to classify the 
stars according to their chemistry. In the case of type stars of some of the groups 
lists have been given! of the wave-lengths and probable origins of the lines on which 
the classification is based. The type stars thus dealt with represent the groups of 
higher temperature, viz., a Cygni (Cygnian), Rigel (Rigelian), ^ Tauri (Taurian), 
Bellatrix (Crucian), e Orionis (Alnitamian), and Sirius (Sirian), 
The spectrum of stars of the Polarian type—representing a temperature stage next 
lower than that of a Cygni,—-is, so far as the relative intensities of the metallic lines 
are concerned, closely allied to that of the chromo,sphere. It is also interesting as the 
connecting link between the specti'um of the Aldebarian stars, in which the arc lines 
of the metallic elements predominate, and that of a Cygni, chiefly composed of the 
enhanced lines of some of the metals. It has hence been thought important to make 
a careful reduction of the spectrum of a star of this group. Of the existing 
photographs of Polarian type spectra at Kensington, that of y Cygni is the best 
for the purpose of reduction, and for this reason ]ias been selected. 
Method, of Reduction. 
The wave-lengths have been determined by measuring the relative positions of the 
lines on the plate with a micrometer, and subsequent use of Hartmann’s interpolation 
formula. In selecting the lines to be used as bases for the reduction, only sharply- 
defined lines with well-authenticated origins, and of the simple nature of which there 
* ‘Roy Soc. Proc.,’ vol. 65, p. 186. 
t ‘ Catalogue of 470 Brighter Stars,’ published by the Solar I’hysics Committee. 
VOL. cci.— A 337. 
19.6.03 
