An electrically conducting powder was produced by mixing bronze spheres with a small amount of carbon black powder. The potential difference across beds of this powder was measured under static conditions and vibration. The system was very sensitive and monitored changes during vibration cycles at rapid rates. Horizontal and vertical conductances were measured. above a minimum vertical stress, the ratio of the two was constant. The conductance was related to vertical stress by a linear relationship with hysteresis, for both static conditions and vibration at small accelerations. A simple model has been proposed to describe this system. At high accelerations (< 10 m/s(2)) changes were much larger. There were permanent changes in conductance and the system was non-linear. The data demonstrate that the internal structure of a particle bed displays great sensitivity, hysteresis and a dependence upon stress history.