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66 incurring any risk of the points touching by any chance vibration, which would make it disappear intermittently. By a methodical process of trial and error, which sometimes demands much time and patience, one succeeds in getting a spark both regular and very feeble; it is then sensitive to the action of "N" rays. If one directs on it a pencil of these radiations, proceeding from any source, one sees the patch on the ground glass increase in size and glow; at the same time its central part becomes more luminous, appearing wrapped in a kind of nimbus. One can then proceed with the photographic experiment. I made about forty such experiments, employing in turn, as sources of "N" rays, a Nernst lamp, compressed wood, hardened steel, Rupert's drops, etc. I have varied the experiments in different ways—for example, by changing the side of the screen CD, by using a zinc screen transparent to "N" rays, etc. Several eminent physicists, who have been good enough to visit my laboratory, have witnessed them. Of these forty experiments, one was unsuccessful: the rays were produced by a Nernst lamp, and instead of