Abstract
We have studied the spectrum of light scattered by surfaces waves thermally excited on the free surface of a nematic liquid crystal in a magnetic field near a second order nematic to smectic A phase transition. We have measured the surface tension and three viscosity coefficients. One of the viscosities diverges and its critical behaviour has been followed to within 3 mK of the transition. The measured critical exponent is consistent with mean field theory for the two studied liquid crystals : cyanobenzilidene octyloxyaniline (CBOOA) and octyloxycyanobiphenyl (M 24)