S. Velorum. 23 



L_S. VELORUM. 

 II.— LIGHT CURVE OF S. VELORUM. 

 III.— GRAPHICAL DETERMINATION OF THE ORBIT OF 

 AN ALGOL VARIABLE. 



By Alexander William Roberts. 



(Read October 30, 1895.) 



I. — S. Velorum. 



This remarkable variable was discovered at the Cape Observatory 

 by Mr. C. Ray Woods when comparing photographic plates taken on 

 the nights of March 18, 1893, and January 20, 1894. 



Dr. Gill was good enough to telegraph to me its variation 

 immediately on its discovery, but it was not till the night of the 1st 

 of February, 1894, that the interesting nature of its variation was 

 manifest here. The minimum which took place on that night was 

 also observed at the Royal Observatory, and the determination of 

 the period and type of variation was fully confirmed by the Love- 

 dale observations. 



Since then S. Velorum has been regularly observed both at the 

 Cape Observatory and at Lovedale ; at the former place by photo- 

 graphy, and at the latter by the usual method of eye determinations 

 of brightness. In this respect that photographic and visual 

 measures have been carried on concurrently, the observations of 

 S. Velorum are unique. No other variable has been systematically 

 observed by photography, and it is to the credit and honour of the 

 Cape Observatory that in this as well as in many another line of 

 investigation, it has led the way, — and kept the lead. When we con- 

 sider the traditions, the instrumental equipment, and the personnel 

 of the Cape Observatory, it is probably no exaggeration to say that 

 the series of measures initiated and carried on there, of S. Velorum, 

 will be to variable star astronomy what the photographs of the comet 

 of 1882 were to sidereal photography. 



It is of course true that isolated photographs of variables have 

 been taken at Arequipa, Harvard, and Mount Hamilton, and recently 

 a series of measures by photography of (3 Persei was made at the 

 Lick Observatory to test the relative accuracy of photographic and 

 eye estimates. But the method adopted (though perhaps in a way 

 necessitated by the brightness of fi Persei) was not one calculated to 



