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