The experiments described below were under-taken to follow up the observation, made independently by Dr Chadwick and one of us (M. L. O.), that the disintegration by sputtering of a plane cathode in a gas discharge was not uniform but showed a maximum at a small distance from the edge. By running the discharge for many hours under steady conditions it was possible to remove a narrow ring of metal at a distance of about a millimetre from the edge of a thin platinum cathode, the middle portion and the extreme edge remaining whole. A photograph of a cylindrical cathode taken by Kaye shows the same effect very clearly.