Pearson and Lamberton used a streak camera to verify the sequence of events. As the voltage was erected across the electrodes, field emission from the thin wire resulted in a sheet discharge between itself and the anode. Since the subsequent main discharge started from the cathode, it was suggested that photoemission was the initiating mechanism. Subsequently, other workers had demonstrated alternative methods for achieving preionisation. These included dielectrically isolated wires and electrodes, sliding spark arrays, electron beams and pins impedance-loaded with capacitors.