State space and entropy rate of a discrete non-equilibrium system are shortly considered including internal variables and the contact temperature. The concept of internal variables in the context of non-equilibrium thermodynamics of a closed discrete system is discussed. The difference between internal variables and degrees of freedom are repeated, and different types of their evolution equations are mentioned in connection with G\'{ e}rard A. Maugin's numerous papers on applications of internal variables. The non-equilibrium contact temperature is recognized as an internal variable and its evolution equation is presented.
Categories: physics.class-ph cond-mat.stat-mech