1901-2.] Dr A. W. Eoberts on Algol Variation. 
77 
Before dealing with the immediate interpretation of the main 
features of the light curve of C.P.D. - 41°*4511, it may be of 
interest to indicate the equations which relate light variation ta 
orbital movement. And I may be allowed to state these rela- 
tions in the form I have found most serviceable in my own 
investigations of Southern Algol variables. 
Other equations more precise and more elegant will no doubt 
occur to those interested in such investigations. Still, in practi- 
cal work, the convenience of any expression is not its least 
merit. 
In fig. 3 we have the representation of the real orbit of an 
Algol binary star. 
In this typical system let — 
A. = angular distance of periastron from line of sight. 
v = true anomaly, POS. 
0 = angular distance of star from line of sight, LOS. 
= (A + v). 
1 = inclination of orbit, 
e = eccentricity of orbit. 
8 = projected or apparent distance between centres 
of component stars. 
Then 
(1) S=— ? - — - — \/l - cos 2 l cos 2 0. 
1 + e cos v 
In fig. 4 we have the projection of the system on a plane at 
right angles to the line of sight. 
Fig. 4. 
Let the position of the two discs represent the eclipse of com- 
ponent S (1) by component S (2) . 
