Theory of Surface- Forces. 
431 
half the sum p 
_ Pi+Pi 
of the maaimumjmd minimum pressure 
and the reciprocal value of the density for every point of the 
Fig. 8. 
capillary layers, which envelops the spherical drops and the 
spherical vapour-bubbles, the minima of these curves present 
exactly the unstable part Aj FB 6 8 of the theoretical isotherm 
of James Thomson. 
The densities o£ the unstable phases of the isotherm 
are thus present in the considered capillary layers under 
a system of pressures, which are dependent on the direction, 
the maximum and minimum values of these pressures being 
respectively in the direction of the lines of forces and 
perpendicular to the latter. The theorem above gives thus 
the physical meaning of the unstable part of the theoretical 
isotherm of James Thomson. 
2 G2 
