  Early work on kinetic theory by W. Herepath and J. Waterston was virtually ignored, but the work of A. Krönig made kinetic theory a lively topic in physics. J. C. Maxwell made a major advance by deriving from some simple postulates a law for the distribution of velocities of the molecules of a gas when it was in equilibrium. Both Maxwell and L. Boltzmann went further, and in different, but related, ways derived an equation for the approach to equilibrium of a gas. The equilibrium distribution earlier found by Maxwell could then be shown to be a stationary solution of this equation.