The evolution of the concentration profile in a gravitational field ne
ar the critical consolute point is studied by refractive index measure
ments. The dependencies of the relaxation time on the distance to the
critical level and temperature change are obtained. The decreasing of
equilibration time for refractive index gradient is observed, while th
e critical level is approached. This result contradicts with well-know
n ''critical slowing down'' due to vanishing of diffusivity coefficien
t at the critical consolute point. The proposed theoretical interpreta
tion of this phenomena is based on key role of the critical layer with
the highest concentration gradient and its width in gravitational fie
ld. The decreasing of the width of critical layer results in speeding
up of equilibration in the nearest vicinity of the critical point. The
quantitative agreement of relaxation time dependencies with this theo
retical analysis is found. (C) 1998 Elsevier Science B.V.