We present a light scattering measurement of the correlation length for a series of critical solutions of polystyrene in methylcyclohexane with different molecular weights. Our results show that the correlation length xi similar to N(zeta)nu epsilon(-0.63), where N is the polymerization index and epsilon =(T-T-c)/T-c is the reduced temperature. The N exponent zeta(nu) is found to be 0.18+/-0.02, which is contrary to most earlier direct experimental results but in excellent agreement with theoretical predictions by de Gennes and Stepanow.