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IN a recent commimication in Nature, Medley1 presents new evidence on the importance of gas discharges in modifying the process of frictional electrification. One might suppose that, when such discharges occur, the application of a strong electric field to the rubbing surfaces would alter the electrification produced. Morris-Jones2 failed to find such an effect, whereas Gill and Alfrey have reported its existence in a letter in Nature3. Morris-Jones worked with flannel, silk and chamois leather; Gill and Alfrey worked with ebonite and sand. Medley's interpretation of his own experiments suggests that the contradictory findings concerning the effect of an electric field can be explained by assuming that the materials used by Morris-Jones were sufficiently humid for poor insulation to have limited their charging to a value below that at which gas discharge would have set in, whereas Gill and Alfrey's materials were sufficiently dry for gas discharge to have played a part. The nature of the materials in question supports this interpretation. If it be accepted, then the experiments of Gill and Alfrey do not give information (as they claim) about the cause of frictional charging, but only about the subsequent partial discharging. In particular, the experiments are not valid evidence for the existence of a metal/insulator contact potential.