696 
PROFESSOR J. R. LOCKYER OR THE PHOTOGRAPHIC 
has appeared at Kensington. In the case of Rigel photographs have been taken 
October, 1890, and October, 1892, and the spectrum has remained constant. Dupli¬ 
cates of y, S, e, and ^ Orionis and y8 Tauri have also been obtained, without any 
changes being detected. 
It has been a common practice to call the stars of this type “ Orion stars,” it being 
supposed that they were confined to the constellation Orion. We now know, however, 
that they are distributed in nearly all parts of the northern celestial sphere. 
(2.) Sub-division (B. 
Characteristics of the S^oectra. 
In the stars of this sub-division the hydrogen lines are not quite so broad as in stars 
like Sirius, though they are much broader than in those like the Sun. Besides the 
lines of hydrogen, all the principal lines of the solar spectrum can be made out, but 
they are much finer than in the stars like tlie Sun. The metallic lines appear to be 
stronger when the hydrogen lines are finer and vice versa. 
Examples are shown in Plate 28. 
a Aquilse and a. Ophiuchi have been included in this list, although they have 
particularly hazy lines in their spectra. These lines, however, agree in position with 
those of stars in Sub-division y. In the case of a Aquihe Professor Pickering has 
also noticed that the lines are hazy, and has suggested that this may be due to the 
very rapid rotation of the star, the axis of rotation being at right angles, or nearly so, 
to the plane passing through the star and the Sun."^ It is evident that such a 
rotation would broaden all the lines, and that the fainter lines would most probably 
disappear. 
A special series of photographs of the spectrum of a Aquilaj is being taken at 
Kensington in order to determine whether the haziness of its spectrum lines is 
invariable. 
Arrangement in Order of Differences. 
The stars of this sub-division do not difier essentially from each other, the only 
difference being in the relative thicknesses of the hydrogen and the metallic lines. 
Arranging the stars in the order of difierences they may be further sub-divided as 
follows :— 
‘ Annals of Harvard College Observatory,’ vol. 26, p. 21. 
