374 SECTIONAL TRANSACTIONS.—A. 
gaseous envelope star Z Andromede, discovered at Victoria. In the discussion 
these and the much more numerous earlier observations are treated in an attempt 
to determine (a) the mode of excitation of the nebular radiation and (6) the 
nature of the carrier of the ‘nebulium’ spectrum, in particular if it is a 
H He molecule. 
47. Mr. J. Jackson.—Photographic Proper Motions of Faint Stars. 
During the past year the Zone centred at 65° N.Dec. has been photographed 
with the 13-inch astrographic telescope at the Royal Observatory, Greenwich, 
for the determination of proper motion by comparison with the original astro- 
graphic plates taken about thirty years ago. The new plates are taken through 
the glass—t.e., with the film side of the plate away from the object glass of the 
telescope. The new and old plates are then placed film to film and the relative 
position of the stars measured. All the plates on this Zone have now been 
measured, so that it is possible to deduce the proper motion of all stars between 
64° and 66° N.Dec. down to about the twelfth magnitude. Most proper motions 
of the order ot 3” a century can be detected with certainty. The following 
short table shows the number of stars found with a proper motion exceeding 
5” a century in the second half of the Zone R.A. 12h. to 24h. :— 
Centennial Proper Motion. 
No. of stars 
in Catalogue 5’’-10” 10’-15” 15’-20” 20”-30” 30-50” 50” 
10,192 533 87 38 20 10 1 
The results are being discussed for systematic motion of the stars. 
48. Dr. RB. K. Youne and Dr. W. E. Harreer.—Methods and Results 
of Spectroscopic Absolute Magnitude Determinations. 
The paper presents the results of an investigation ito the methods of 
determining parallaxes by the spectroscopic method and gives results for 1,105 
stars. The spectra of 500 stars of known parallax were used to calibrate the 
empirical curves relating line intensity to absoiute magnitude; new lines showing ~ 
the effect were found, and fourteen have been used in the work. A standard 
scale showing absorption lines of graded intensity was used in estimating line- — 
ratios. Proper motions were used as a check upon the results of groups of 
stars. Substantial agreement exists with Mount Wilson except in the late 
K-giants, where we have a greater range in brightness. 
Me ame ee 
49. Dr. F. Henroteav.—The System of o Scorpii. 
As a result of several years’ study, it appears probable that o Scorpii is an 
interesting triple system. First it was found by Father Selga that a considerable 
variation of radial velocity existed, having a very short period (about six — 
hours). The star is thus of the B Canis Majoris type or, as we have reason — 
to suppose, an extreme case of Cepheid variation. The short-period radial — 
velocity variation cannot be attributed to orbital motion. e 
A longer period of radial velocity variation (about thirty-four days) due 
to orbit motion was then discovered, long-period curves being determined in ~ 
the years 1918, 1920, 1921, 1922, 1923, and 1924. Remarkable changes of shape 
and amplitude occur in them. Theoretical researches made in 1921 indicate that — 
large perturbations in the orbit could not be due to a possible non-spherical — 
shape of the primary body. 
At present we find indications of the existence of a more remote third body— 
that is, of a motion in a longer period orbit (probably in the neighbourhood 
of five years). This is found not from the variation of radial velocity, but 
from the fact that the maxima or minima of the short-period radial velocity — 
curves come some years sooner, other years later, than the predicted ones; in 
other words, there is a very marked equation of light which from its variation 
permits us to compute elements of the long-period orbit. > 
= 
