ON THE SPECTRIFM OF y CYONI. 
211 
metallic arc lines, as distinguished from the enhanced lines. These, which occur so 
prominently in a Cygni, are, with certain excerptions, present also in y Cygni, so that 
the latter spectrum practically consists of the a Cygni spectrum (with modifications 
of the intensities of the enhanced lines of various metals) with the ordinary arc lines 
added, and the two sets are of about equal importance. This is a condition of affairs 
intermediate to that of the Aldeharian stars—in which the ordinary lines are well- 
developed and the proto-metallic lines weak or missing—and a Cygni, where the 
enhanced lines are very prominent, to the nearly total exclusion of the metallic arc 
lines. 
The only line of any prominence which occurs solely in a Cygni is the silicium line 
\4131H This is one component of the silicium double which is so conspicuous in tlie 
spectra of a Cygni, Rigel, Sirius, &c. There is certainly a line in y Cygai apparently 
coincident with the other component A. 4128‘1, hut in the absence of its companion it 
must he concluded that the y Cygni line in question has probably an origin entirely 
distinct from silicium. The silicium double mentioned is also absent from the 
chromospheric spectrum, which closely resembles that of y Cygni. 
In a paper “ On the Order of Appearance of Chemical Substances at different 
Stellar Temperatures,”^ it was pointed out that the enhanced lines of the various 
metals attained a maximum intensity at varying levels of the stellar temperature 
sequence. The present detailed investigation of the y Cygni spectrum confirms this 
result, the enhanced lines of strontium, scandium, and titanium being at their 
strongest in y Cygni and much stronger than in a Cygni, while in the latter spectrum 
the enhanced lines of iron, chromium, and magnesium, attain their maximum 
intensity, being more prominent than in y Cygni. 
Of the better known arc lines of some of tlie metals whicli are prominent in 
y Cygni, but-very weak or lacking in a C!ygni, the following may Ije mentioned : the 
iron triplets (\X 4045-98, 4063-76, 4071-91) and (XX 4383-72, 4404-93, 4415-29); the 
manganese quartette (XX 4030-92, 4033-22, 4034-64, 4035-80) ; the chromium triplet 
(XX 4254-51, 4274-96, 4289-89); the aluminium pair (XX 3944-16, 3961-67); tlie 
calcium line, X 4226-90 ; and the barium line, X 4554-21. 
General Conclusions. 
The investigation of the photograjDhic spectrum of y Cygni in its relation to otlnn- 
spectra has led to the following conclusions :— 
]. The majority of the lines are due to metallic vapours, the enhanced lines and 
the arc lines being of about equal prominence. 
2. The temperature conditions are thus intermediate between those of Aldebaran 
* ‘ Roy. Soc. Proc.,’ vol. 64, p. 396, 
2 E 2 
