ing 12d 21h 47m, the
orbit is sensibly eccentric, and the two spheroids are not so much
elongated as was the case with RR Centauri. The mass of the system is
enormous, one of the two stars being 10 times and the other 21 times as
heavy as our sun.

Further illustrations of this subject might be given, but enough has
been said to explain the nature of the conclusions which have been drawn
from this class of observation.

In my account of these remarkable systems the consideration of one very
important conclusion has been purposely deferred. Since the light-curve
is explicable by eclipses, it follows that the sizes of the two stars
are determinable relatively to the distance between them. The period of
their orbital motion is known, being identical with the complete period
of the variability of their light, and an easy application of Kepler's
law of periodic times enables us to compute the sum of the masses of the
two stars divided by the cube of the distance between their centres.
Now the sizes of the bodies being known, the mean density of the whole
system may be calculated. In every case that density has been found to
be much less than the sun's, and indeed the average of a number of mean
densities which have been determined only amounts to one-eighth of that
of the sun. In some cases the density is extremely small, and in no case
is it quite so great as half the solar density.

It would be absurd to suppose that these stars can be uniform in
density throughout, and from all that is known of celestial bodies it
is probable that they are gaseous in their external parts with great
condensation towards their centres. This conclusion is confirmed by
arguments drawn from the theory of rotating masses of liquid. (See J.H.
Jeans, "On the density of Algol variables", "Astrophysical Journ." Vol.
XXII. (1905), page 97.)

Although, as already explained, a good deal is known about the shapes
and the stability of figures consisting of homogeneous incompressible
liquid in rotation, yet comparatively little has hitherto been
discovered about the equilibrium of rotating gaseous stars. The figures
calculated for homogeneous liquid can obviously only be taken to afford
a general indication of the kind of figure which we might expect to find
in the stellar universe. Thus the dotted curve in Fig. 5, which exhibits
one of the figures which I calculated, has some interest when placed
alongside the figures of the stars in RR Centauri, as