134,135] Stability of Liquid Stars 147
where f(T, p) depends not only on T and p, but also on the particular type
of matter of which the star is made.
From this formula we can calculate the value of G for each configuration
on the line MM' and can represent each value of G, measured as an emission
of radiation, by a point P' either vertically above or vertically below the
point P to which it refers. Corresponding to any one specified type of
matter, the various points P' will form a line such as A A' (which, for
diagrammatic simplicity, has been drawn as a straight line). We may call
A A' a “generation line” corresponding to the “emission line” MM'. There
is a different “generation line” for each type of stellar material, but the
“ emission line ” is fixed by the mass of the star, except for small variations
of the type we had under consideration in §§ 95-97, such as might arise from
a redistribution within the body of the star of its energy-generating material
or its radiation-stopping atoms. We must be content to disregard such small
variations in the present investigation.
The intersections ST of a generation line A A' and the corresponding
emission line MM' represent configurations at which E = G, and so determine
the possible configurations of equilibrium for a star of given mass, made of
that special type of matter to which the line A A' refers.
As a star ages and its more readily transformable material becomes
exhausted, the line A A' will move downwards. Corresponding to certain