  This argument shows that Boltzmann was already implicitly embarking on an approach that differed from the context of the 1872 paper. Recall that this paper used the concept of probability only in the guise of a distribution function, giving the probability of molecular velocities. There was no such thing in that paper as the probability of a state of the gas as whole. This conceptual shift would become more explicit in Boltzmann's next paper (1877b).