Ultrasonic Relaxation Studies in the Liquid Crystal 80CBThe variation of the ultrasonic velocity with temperature in the liquid crystal 4'-n-octyloxy-4-cyanobiphenyl (80CB) at four different fixed ultrasonic frequencies is studied. From these studies various relaxation paranieters like the adiabatic relaxation time, velocity a t zero frequency, in the vicinity of isotropic-nematic phase transition and velocity a t infinite frequency are estimated. From these parameters the relaxation mechanism in the vicinity of isotropic-nematic phase transition is studied and the results are discussed.