  We point out that, contrary to signs of heat capacities, thermodynamic
fluctuations are simply and unequivocally related to onset of instabilities
that show up near critical points. Fluctuation theory is then applied to \Schw\
\bh s surrounded by radiation. This shows that slowly evolving \bh s along
quasi-equilibrium states in cavities greater than $10^6$ Planck length will not
evaporate below the critical Hawking limit temperature despite the fact that
pure radiation has a much higher entropy. (CQG in press, figure request to
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