When equilibrium is reached in a reaction system (containing an arbitrary number of components and reaction paths), as many atoms, in their respective @M03986@ will pass forward, as well as backwards, along each individual path in a given finite time interval. Accordingly, the @R05174@ in the reverse direction must in every detail be the reverse of the @R05174@ in the forward direction (provided always that the system is at equilibrium). The principle of detailed balancing is a consequence for macroscopic systems of the principle of @M03916@.