We have performed small-angle Rayleigh-scattering measurements in toluene subject to a large stationary temperature gradient ∇T. The experiments demonstrate the presence of long-range entropy and viscous fluctuations enhancing and modifying the Rayleigh spectrum. The experiments confirm that the viscous-heat-mode contributions vary with (∇T${)}^2$/$q^4$, where q is the wave number of the fluctuations. The observed amplitudes of both the entropy and viscous fluctuations are in excellent agreement with the theoretical predictions for the fluctuations in nonequilibrium fluids.

• Received 11 August 1989

DOI:https://doi.org/10.1103/PhysRevA.41.816