In any spontaneous irreversible change, if the system is heat-isolated, there must be an increase of entropy.
(5) If we might also regard the couple as a reversible thermodynamic engine for converting heat into work, and might neglect irreversible effects, such as conduction, which are independent of the current, we should expect to find the ratio of the heat absorbed at the hot junction to the heat evolved at the cold junction, namely, PIP', to be the same as the ratio T/T of the absolute temperatures of the junctions.
But apart from the fact that the authority of the Privy Council, as not being a "spiritual" court, is denied by many of the clergy, no one claims that its decisions are irreversible in the light of fresh evidence.
An irreversible process which permits a more complete experimental investigation is the steady flow of a fluid in a tube already referred to in section to.
Nevertheless, the relations obtained in reversible cases such as sulphur have not yet found application in the highly interesting cases of ordinary irreversible isomerism.