26 Transactions of the South African Philosophic al Society. 



A solution of this equation gives the ratio of the light of the com- 

 panion to the central star as 4 : 1. 



Then again we notice that while it takes only 4 hours for the 

 secondary star to pass from simple contact to total eclipse, it takes 

 nearly 10| hours to pass behind the larger star ; that is, the diameter 

 of the central star is 2-| times greater than that of its companion. 

 And we have seen that it is four times fainter. 



Further, as the time of passing across the primary is 10J hours, 

 and the whole period 142-4 hours, we have a relation between the 

 diameter of either star and the major axis of the orbit, or rather with 

 the diameter of the orbit, for any data on which we could rest a 

 determination of eccentricity is exceedingly uncertain. The distance 

 between the two stars is probably not much greater than twice the 

 diameter of the central star, a contiguity utterly unknown in the 

 solar system. The tidal action and interaction in such a system must 

 be enormous. 



So far we have proceeded on the safe foothold of ascertained data. 

 An assumption as to the mass of S. Velorum would yield the 

 dimensions of the system expressed in terms of the sun's distance 

 from the earth. Such an assumption would, however, practically be 

 a mere guess. Indeed all we can say concerning the absolute size of 

 the S. Velorum system is that its semi-diameter cannot be greater 

 than 10,000,000 miles or less than 1,000,000 miles. 



A spectroscopic examination of the star's light would give an 

 absolute determination of the dimensions of the system were it a 

 bright one. At present, however, it is impossible to tell the motion 

 in the line of sight of 8th and 9th magnitude stars. But when we 

 remember the progress that has been made in spectroscopic science 

 during the past fifty years, we are warranted in the confident hope 

 and belief that before a few more decades have passed away we 

 shall be able to deal with motion in the line of sight of even 9th 

 magnitude stars. 



It may be mentioned that observations here of S. Velorum during 

 the next few months will be directed specially to the determination, 

 if possible, of a secondary minimum. 



As the companion passes behind the central star we have the 

 minimum phase described in this paper, but when the companion 

 crosses the line of sight in front of the primary star it will be pro- 

 jected on the primary star, and we will have, theoretically, a 

 secondary minimum. 



Whether this minimum can be measured is another matter. It 

 means only a fall from 7*75 mag. to 7*81 mag., a difference of 

 - 06 magnitudes, and the amount of difference in intensity that a 

 practised eye can distinguish is, according to Dr. Gould, 0-06 mag. 



