1901-2.] Dr A. W. Roberts on Algol Variation. 
79 
separate the principal and secondary minima, then the orbit of 
the system is circular. 
As a rule, the eccentricity of Algol binary stars is small. 
Then, again, if the light of the star is stationary at either 
minimum, a relation is at once established between the dimensions 
of the two component stars. 
If r 1 =H and the orbit is circular, the above equations become 
very much simplified in form. They become — 
(5) 
( 6 ) 
(7) 
(8) 
( 4 ) 
COS cf) =1 
8 = ^/l - cos 2 t cos 2 0 . 
8 
2 T 
COS l 
\/ 1 - 
sin 2 </> 
cos 2 cf> cos 2 K 
L„ = 1 - L,( ~ sm ^ 
1 - L„ 
2 cf> - sin 2 A 
M 0 = 2-5(10 -Log L 0 ) + M 
The date when eclipse begins or ends yields yet another relation; 
for let 
P = period of variable. 
T m = date of minimum phase. 
T 0 = date when eclipse begins or ends. 
Tr __(±T o + T w )360°. 
iv p , 
then 
(9) 2 r— Jl - cos 2 t cos 2 K . 
We may now apply the foregoing formulae to the particular 
case of the light curve of C.P.D. — 41°*45 1 1, as exhibited in 
%. (2), PI. II. 
An examination of the light curve indicates that the star passed 
its minimum on 
h. m. 
July 2, 16 17 (C.M.T.) 
We also find that the descending and ascending phases are 
similar, both portions of the light curve being symmetrical on 
either side of the minimum. 
