Slow (logarithmic) relaxation from a highly excited state is studied in a H
amiltonian system with many degrees of freedom. The relaxation time is show
n to increase as the exponential of the square root of the energy of excita
tion, in agreement with the Boltzmann-Jeans conjecture. while it is found t
o be inversely proportional to residual Kolmogorov-Sinai entropy, introduce
d in this Rapid Communication. The increase of the thermodynamic entropy th
rough this relaxation process is found to be proportional to this quantity.