This paper reports calculations and analysis of the effects of a perfect
conducting wall of a very large spherical shell on the stable thermodynamic
equilibrium of a black hole sitting at the centre of the shell which is filled
with Electromagnetic blackbody radiation. A parallel is drawn with the case
where electromagnetic is replaced by scalar blackbody radiation with Dirichlet
or Neumann boundary conditions on the wall. It is found that the value of the
shell radius above which only blackbody radiation remains in stable
thermodynamic equilibrium can be considerably affected by vacuum polarization
due to the presence of the wall.Comment: 8 pages, no figure