42 Transactions of the South African Philosophical Society. 



examined the image with a microscope ; it was perfectly normal, 

 making the variability of the star highly probable. Professor 

 Kapteyn communicated these facts to Sir David Gill, who kindly 

 gave me the matter for further investigation. As this star falls 

 within the Cape zone of the Carte die del, there were a number of 

 plates available for a further examination without recourse to the 

 sky. I examined these, twelve in number, but found no certain 

 difference of magnitude. But my first telescopic observation on 

 Feb. 20, 1899, caught the star at a low magnitude (10-5) ; this was 

 fortunate, as I did not secure another minimum for sixteen months. 

 Had my first observation not happened as it did, the confirmation 

 •of variability and Dr. Eoberts's interesting paper might have been 

 •delayed many years, as both the Carte die del plates and my other 

 visual observations extending over sixteen months offered no evi- 

 dence of change of magnitude. 



At the Cape Observatory we have now secured in all nine 

 observed minima covering 2,202 periods in 4,083 days, yielding a 

 period of — 



Id. 20h. 30m. 2-9s., 



a difference from Dr. Eoberts's result of only one-tenth of a second — 

 .a quantity far smaller than the probable error to w^hich such deter- 

 minations are liable. 



