English: Diagram of a Brownian ratchet, also known as a Feynman-Smoluchowski ratchet. This illustrates a Maxwell's Demon that produces useful work from the random thermal motion of molecules at a finite temperature in apparent violation of the Second Law of Thermodynamics. Molecules that impinge the paddle wheels would rotate the shaft in one direction only. Feynman and others did a detailed analysis that proved that no work will be done if T1 = T2, thus vindicating the second law.