82 Proceedings of Royal Society of Edinburgh. [sess. 
tidal forces, gone apart, one or two diameters, in their long spiral 
journey. 
We may now collect under one statement what has been 
ascertained concerning the star C.P.D. - 41°*4511 from an ex- 
amination of its light curve. 
(1) The star is a close binary system, revolving in a circular 
orbit in 44 hours 30 minutes. 
(2) This orbit is inclined 5° 43' to the plane of sight. 
(3) The two component stars are apparently equal in size, but 
not in brightness. 
(4) If the combined brightness of both stars be considered as 
equal to unity, then the brightness of one component is 0*860, 
and of the other 0*140. That is, one star is six times brighter 
than the other. 
(5) If the distance between the centres of the two component 
stars be regarded as unity, then the diameter of either star is 
0*325. That is, the stars are separated from one another by a 
distance equal to twice the diameter of any one of them. 
(6) The mean density of the system is slightly less than one- 
half that of the sun. That is, it is two-thirds the density of 
water. 
(7) It is impossible to give, and of no value to speculate upon, 
the actual dimensions and mass of the system. 
The star lies far beyond the reach of spectroscopic examination, 
at least with its present limitations. 
We have no means, also, of ascertaining the distance of the 
star, but it is confidently hoped that some observatory, possessing 
the necessary equipment, will undertake the parallax of this and 
all other similar binary systems. 
The test of any result, or group of results, determined directly 
from observations, is the amount of accordance between the theory 
arrived at and the observations from which it has been deduced. 
The salient features of the observed light curve of C.P.D. 
- 41° *45 11 indicate a system such as that set forth. 
In order to ascertain with what completeness the theory con- 
forms to all the facts of variation, we compute a theoretical light 
curve, and compare this theoretical light curve with that actually 
observed. 
