  The rate of change of entropy $\dot S$ is measured for a system of particles
floating on the surface of a fluid maintained in a turbulent steady state. The
resulting coagulation of the floaters allows one to relate $\dot S$ to the
velocity divergence and to the Lyapunov exponents characterizing the behavior
of this system. The quantities measured from experiments and simulations are
found to agree well with the theoretical predictions.

Chaotic Dynamics