On the application of the Onsager-Machlup function to non-linear fluctuations of a thermodynamic variable

The application of the Onsager-Machlup principle to non-linear fluctuations of a thermodynamic variable is discussed. The Onsager law of proportionality of fluxes and forces is obtained by an integral method. Approximate calculation of the transition probabilities and of the most probable evolution are made by taking the diffusion coefficient as a smallness parameter. The results are compared with results obtained by other methods, particularly by Kubo, Matsuo and Kitahara. The asymptotic case of infinite time intervals is discussed summarily.