Unable to furnish any reason why the electric radiation of a distant spark should reduce the resistance of pulverised carbon I refrained from publishing the bare observation in the hopes of finding an explanation by further experimentation, merely noting to friends the delicacy of the pulverised carbon rheostat as a detector of Hertzian waves and making some further experiments with it and a telephone receiver in circuit in this direction. The recent publication of the brilliant researches of Dr. Oliver J. Lodge now makes the entire matter clear. Dr. Lodge describes a new form of microphonic detector of Hertzian waves, consisting of two or more pieces of fairly clean metal in light contact and connected to a voltaic cell, a film of oxide of the metal intervening between the surfaces, “so that only an insignificant current is allowed to pass.” He writes: “Now let the slightest surging occur, say, by reason of a sphere being charged and discharged at a distance of 40 yards; the film at once breaks down--perhaps not completely, that is a question of intensity--but permanently.” This detector, Dr. Lodge terms a “coherer” because of the partial metallic cohesion above described. Upon this point he says: “A bad contact was at one time regarded as a simple nuisance.” ... “Hughes observed its sensitiveness to sound waves, and it became the microphone. Now it turns out to be sensitive to electric waves, if it be made of any oxidisable metal (not of carbon) and we have an instrument which might be called a micro-something but which, as it appears to act by cohesion, I call at present a coherer.” The cohesive result between the metallic surfaces is also referred to as a “welding effect of an electric jerk.” In the volume just published, entitled “The Work of Hertz and Some of His Successors,” reprinted from _The Electrician_, London, this foot note is added on p. 30: “FitzGerald tells me that he has succeeded with carbon also.” My experiments would seem to fully demonstrate that carbon as well as metals may act as coherers. At some recent trials the editors of the _Electrical Engineer_ were present and were fully satisfied as to the swinging up of the needle of the milliamperemeter and the click in the telephone receiver, by repeated tests. The experimental side of the subject has been so exhaustively and admirably presented by Dr. Lodge (detailed in the publications referred to) that what is here said has no more than a secondary interest. But it may not prove amiss to gather together all the evidence which tends to demonstrate the influence of disruptive discharges upon neighbouring bad contacts conveying currents. As Lodge points out, fuses may easily be “blown out” in this manner. This has occurred to me on a number of occasions with 10 ampere fuses. Under proper conditions of sparking surfaces and circuit a short spark might suffice.