Motion pictures of tree breakdowns between needle points

Most of this presentation consisted of a motion picture of 21 tree-breakdowns between needle points about 1 mm. apart in strips of the following materials about l/8 inch thick: Three types of polyethylene Unvulcanized natural rubber Transparent polyvinyl chloride Polystyrene Unvulcanized Butyl Rubber Polyurethane The growing trees were photographed by transmitted light, so that the microchannels looked black. An ordinary 16 mm. movie camera was mounted over the microscope and focussed on infinity. Voltages up to 20 KV AC were chosen to give the desired rate of tree growth. All pictures were made at the actual speed, not by time lapse photography. Figure 1 shows frames including the breakdown flash. Immediately after this a balloon-like dark figure formed and quickly disappeared. This was caused by a lens effect of the hotter polyethylene that deflected the transmitted light. There was no carbonization.