98 Proceedings of the Royal Irish Academy. 
Etoiles a Spectres de la Troisieme Classe (Stockholm, 1885), and is as 
follows : — 
Class I. includes spectra, in which the metallic lines are ex- 
tremely faint {faihles) or entirely invisible. The blue and violet of 
the spectrum are strong, and the colour of the stars is usually white. 
This class is subdivided as follows : — 
l.a. Spectra in which the hydrogen lines are very strong (as in 
Yega, Sirius, &c.). 
I. h. Spectra in which the hydrogen lines are wanting. 
I. c. Spectra where the hydrogen lines, and the line D3 are brghti 
(as in p Lyrae and y Cassiopeiae). 
Class II. includes spectra in which the metallic lines are numerous 
and easily visible. The blue and violet are relatively weak. In the 
red there are sometimes faint bands. This class is subdivided into — ! 
II. a. Spectra with numerous metallic lines, especially in the yellow | 
and green (Aldebaran, Pollux, Arcturus, &c.). \ 
i 
II. h. Spectra where, besides the dark lines and isolated bands, there 
are numerous bright lines (ex. T Coronse, E. Geminorum). 
Class III. includes spectra in which, besides the metallic lines, there 
are numerous dark bands in all parts of the spectrum, and the blue 
and violet are remarkably faint. These stars are orange, or red, in 
colour. This class is subdivided as follows : — 
I 
! 
III. a. Spectra, in which the dark bands have a dark sharp edge I 
towards the violet, and shade away towards the red (as in > 
a Herculis, a Orionis " ^^ova Orionis," a Pegasi, &c.). j 
III. h. Spectra, in which the dark bands shade away towards tbe 
violet (as in U Hydrse, 19 Piscium). . j | 
The sign ! denotes that the spectrum is fine ; ! ! very fine ; and 
! ! ! superb. 
