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It seems intuitively reasonable that Gibbs' variational principle de termining the conditions of heterogeneous equilibrium can be gener alized to nonequilibrium conditions. That is, a nonequilibriurn steady state should be the one that makes some kind of generalized-entropy production stationary; and even in the presence of irreversible fluxes, the condition for migrational equilibrium should still be the equality of some generalized chemical potentials. We summarize progress to date toward this goal, reviewing (a) the early history, (b) work of Onsager and first attempts at generalization, (c) the new direction the field took after 1967 with the work of Tykodi and Mitchell, and (d) the present situation and prospects. Our conclu sion will be, briefly, that the outlook is good in that the basic principles are believed known; but we do not yet �now whether they can be reduced to simple rules immediately useful in practice, in the way that the Gibbs phase rule is useful. For this, we need more experience in the technique of applying them to particular cases, and more data to test some conjectures.
E. T. Jaynes (Wed,) studied this question.