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Rh its electric resistance. The current flowing through the wire is produced by five accumulators; with the aid of high-resistance rheostats, the intensity is adjusted to make the platinum wire a dull red. The wire is stretched between two massive brass pliers, A and B, which are connected to the terminals of a capillary electrometer; on one of the connecting wires an adjustable electromotive force is inserted, obtained by shunting a portion of the circuit of an auxiliary battery. This electromotive force is regulated so that the electrometer is at zero. Every variation in resistance of the platinum wire produces a deviation of the electrometer. Now, with "N" rays playing on the wire, no deviation of the meniscus was observed. The interposition of a lead or wet-paper screen remained without effect on the electrometer, though the wire underwent the usual variations in brightness. This certainly proves that "N" rays do not raise its temperature. I, moreover, assured myself that the method was sufficiently sensitive by the following experiments; by means of a wire rheostat, an assistant varied the resistance of a circuit containing