Using a light-beat laser spectrometer, we observe the relaxation of the thermally excited fluctuations of anisotropy in the nematic phase of $p-\mathrm{azoxyanisole}$. We identify the two low-frequency purely dissipative modes recently predicted. A first study of the angular dependence of the width of these modes allows a determination of three among the six viscosity coefficients introduced by Leslie.

• Received 12 May 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.1361