Measurements are reported, we believe for the first time, of the dynamic surface conduction on humid insulators, resolved as complex impedance plots in the frequency range 0.01-10 kHz, and also of the corresponding time dependence of the charging and discharging currents in the time interval between 100 ~s and many hours, with a range of step voltage amplitudes. The aspect ratio of the surface electrode configuration has been varied over three decades and the magnitude of the impedance, instead of being linear in this ratio as in the classical surface conduction with a uniform surface conductance, is found to follow a power law at small values of this ratio and an exponential law at larger values, suggesting the presence of surface dispersion. The conductance is also exponentially dependent on the relative humidity of the ambient air, suggesting the importance of percolation phenomena. The charging and discharging currents vary very slowly in time and their magnitudes are strongly nonlinear in the amplitude of the step voltage, pointing clearly to the importance of electrochemical storage of charge and of energy, as distinct from the classical electrostatic processes. Phenomena of negative capacitance are seen in certain circumstances. Probing of the space between the electrodes shows the surface potential to be distributed and not to be predominantly concentrated at the electrodes. The behavior of glass, mica, and silicon nitride was found to be very similar. The significance of these observations is discussed in terms of a model involving nonuniform filamentary conduction paths on the humid surfaces.

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