Rayleigh linewidth measurements of xenon are reinterpreted with the help of recent thermodynamic measurements which permit the background contributions to the linewidth to be computed. The resultant values for the critical contribution to the linewidth are shown to be in excellent agreement with the Kawasaki equation. Furthermore, the exponent Φ describing the asymptotic dependence of the thermal diffusivity χ on the reduced temperature is found to have a value of 0.64 in good agreement with the Kadanoff-Swift-Kawasaki prediction χ~ζ-1 where ζ is the range of the density-density correlation function. This result is in marked contrast to the previous result Φ = 0.75 obtained from the same data without background corrections. Possible modifications to the Kawasaki equation due to the functional form of the correlation function differing from the Ornstein-Zernike form are discussed and are shown to be small