(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.
By Carnot's principle, in all irreversible processes, dH/0 must be algebraically less than do, otherwise it would be possible to devise a cycle more efficient than a reversible cycle.
A very important evolutionary principle is that in such secondary returns to primary phases lost organs are never recovered, but new organs are acquired; hence the force of Dollo's dictum that evolution is irreversible from the point of view of structure, while frequently reversible, or recurrent, in point of view of the conditions of environment and adaptation.
Nevertheless, the relations obtained in reversible cases such as sulphur have not yet found application in the highly interesting cases of ordinary irreversible isomerism.