ABSTRACT
Midway through World War II, it became apparent that a better understanding of the motion and interaction of gaseous media with solid objects was needed. The normal kinetic theory of gases was inadequate to describe the additional complex actions originating from the frictional and viscous forces of real compressive fluids. Two different parts of this problem existed. They are identified as nonlinearity, which occurs at high speeds, and nonuniformity, which is the behavior of the mechanics of rarefied gases. Martin Greenspan recognized the inadequacy of the theoretical explanation for the deviation of the gas behavior from the classic theory. His work on propagation of sound in rarefied gases is a classic example of how to examine a complex system for relaxations resulting in a measured dispersion. He was able to show that the Stokes-Navier equation gave a surprisingly good quantitative account of attenuation and dispersion of sound in monatomic gases down to wavelengths approaching the mean free path.
