Abstract
A Monte Carlo computer simulation of the conductivity of a two-dimensional localized interacting system has been made. A plot of d (log σ)/d (log T) against T, on a double-logarithmic scale, shows clearly two distinct regimes, corresponding to nearest-neighbour and variable-range hopping. For the latter, log σT−x with an exponent x equal to 0·31. Mott's law for variable-range hopping is shown to be obeyed down to temperatures where kT is of the order of a twentieth of the Coulomb gap.