How did James Clerk Maxwell use the idea of relaxation time in his theory of gases?

In his 1866 paper, "On the Dynamical Theory of Gases," James Clerk Maxwell introduced the concept of "time of relaxation" to describe the behavior of fluids under stress.1

Maxwell defined the time of relaxation as the duration required for the elastic force generated by the distortion of a fluid to decay to $1/e$ (where $e$ is the base of the natural logarithm) of its initial value. This concept was a foundational step in understanding relaxation phenomena, which generally refer to the delay between the application of an external stress to a system and its subsequent response as it moves toward a new state of equilibrium.12

By quantifying this decay, Maxwell provided a mathematical framework for analyzing how internal forces within a gas or fluid respond over time following a disturbance, a principle that remains essential in modern physics and chemistry for studying molecular processes and energy redistribution.12