IN a recent communication1 concerning the mechanism of growth of the leader strokes preceding spark discharges, Allibone has stated that the leader stroke develops behind a voluminous corona discharge and that the concentrated bright streamer, which is readily photographed, is in the nature of a ‘core' to this corona. The same view has been expressed by ourselves on various occasions and in earlier reports2, and not only have we succeeded in demonstrating beyond doubt the existence of this diffuse corona discharge forming the head of the leader stroke, but we have also been making extensive investigations of its characteristics during the past eighteen months.