Abstract

This paper is concerned with the introduction of statistical concepts in the molecular theory of heat. In particular, we analyse the arguments invoked by Clausius between 1857 and 1862, and the motivation presented by Maxwell in 1860 to introduce his distribution of velocities. We first show that Maxwell's great insight seems to have been the recognition that the dynamical laws of molecular collision and thermal equilibrium could be made compatible only if the theory of heat became statistical. As for Clausius, historians of science have observed that in 1857 he used probabilities to bring regularity to the theory, but have not satisfactorily analysed important features of his use of probabilities in the context of the theory of heat. We show that only in 1862, in order to answer a criticism to his paper of 1858, Clausius gave a meaning to random motion, along the lines proposed by Maxwell, in his paper of 1860