520 
In fig. 1 ja represents the stable part and #5 the metastable part 
or the three singular curves (M) (/,) and (£41). When we consider 
only the stable parts of the curves, then we may say: the three 
curves go, starting from the invariant point, in the same direction. 
In fie. 2 curve (M/) goes in stable condition through the invariant 
point 7, it is represented by aid. The stable part of (/,) is repre- 
sented by za, the metastable part by 7b; the stable part of (41) 
is represented by 7, the metastable part by ca. When we consider 
the stable parts only of (4) and (/,41), then we may say: the 
curves (1) and (44) go in the same direction, starting from the 
invariant point. 
(6) (M) 
ab.) 
Ee 
2 
¢ 
7 
Le 
7 
Fig. 1 Fig. 2. 
We shall express this in the following way: 
Fig. 1. Curve J is monodirectionable ; the three singular curves 
coincide in the same direction. 
Fig. 2. Curve M is bidirectionable; the two other singular curves 
coincide in opposite direction. 
We may show the above in the following way. 
We consider the equilibrium (/,) = M + F4 at different tem- 
peratures and under corresponding pressure. When we take away 
from this equilibrium the phase #4, then it passes into the equi- 
librium Ms; as this equilibrium is represented by curve -~J/)j, the 
curves (J/) and (Ff) therefore, coincide. The same is true for the 
curves (J/) and (E44), so that the three singular curves coincide. 
From this coincidence however we may not yet conclude the 
position of the stable parts of those curves with respect to one another; 
in order to determine this position, we distinguish two cases: 
1. The two indifferent phases have the same sign, the singular 
equilibrium JM is, therefore, transformable into the invariant equili- 
brium and reversally. 
2. The two indifferent phases have opposite sign, the singular 
equilibrium M is, therefore, not transformable. 
Firstly we take the case 1, eonsequently: the two indifferent 
phases have the same sign. 
