Although Boltzmann's H -theorem turned out not to be the absolute proof of the second law of thermodynamics as originally claimed (see Criticisms below), the H -theorem led Boltzmann in the last years of the 19th century to more and more probabilistic arguments about the nature of thermodynamics. The probabilistic view of thermodynamics culminated in 1902 with Josiah Willard Gibbs 's statistical mechanics for fully general systems (not just gases), and the introduction of generalized statistical ensembles.