Molecular ratchets: Verification of the principle of detailed balance and the second law of dynamics

We argue that the recent experiments of Kelly et al. [Angew. Chem. Int. Ed. Engl. 36, 1866 (1997)] on molecular ratchets, in addition to being in agreement with the second law of thermodynamics, is a test of the principle of detailed balance for the ratchet. We suggest experiments, using an asymmetric ratchet, to further test the principle. We also point out methods involving a time variation of the temperature to give it a directional motion.