  Starting from the second law of thermodynamics applied to an isolated system
consisting of the system surrounded by an extremely large medium, we formulate
a general non-equilibrium thermodynamic description of the system when it is
out of equilibrium. We then apply it to study the structural relaxation in
glasses and establish the phenomenology behind the concept of the fictive
temperature and of the empirical Tool-Narayanaswamy equation on firmer
theoretical foundation.
