Signalling through space without wires : being a description of the work of Hertz & his successors . ose together, far too close to stand any voltagesuch as an electroscope can show, could, when a spark passedbetween them, actually cohere ; conducting an ordinary bell-ringing current if a single voltaic cell was in circuit; and, ifthere were no such cell, exhibiting an electromotive force oftheir own sufficient to disturb a low resistance galvanometer * Phil. Mag., Vol. XXXI., p. 225. t E. Branly, Comptes Rendus, Vol. CXI., p. 785 ; and Vol. CXIL, p. 90. WORK OF HERTZ LECTURE. 21 vigorously, a
Signalling through space without wires : being a description of the work of Hertz & his successors . ose together, far too close to stand any voltagesuch as an electroscope can show, could, when a spark passedbetween them, actually cohere ; conducting an ordinary bell-ringing current if a single voltaic cell was in circuit; and, ifthere were no such cell, exhibiting an electromotive force oftheir own sufficient to disturb a low resistance galvanometer * Phil. Mag., Vol. XXXI., p. 225. t E. Branly, Comptes Rendus, Vol. CXI., p. 785 ; and Vol. CXIL, p. 90. WORK OF HERTZ LECTURE. 21 vigorously, and sometimes requiring a faintly perceptibleamount of force to detach them. The experiment wasdescribed to the Institution of Electrical Engineers in 1890,*and Prof. Hughes said he had observed the same thing. The experiment of the syntonic Leyden jars can beconveniently shown with the double knob or 1889 pair of knobs are arranged to connect the coatings of thereceiving jar (a large condenser being interposed to preventtheir completing a purely metallic circuit), and in circuit with. Fig. -Receiver in Syntonic Jar Experiment, with Knob Cohererand Tapper-back (c/. Fig. 4). them is a battery and a bell. Every time the receiving jarresponds syntonically to the electric vibration of the other jar,the knobs cohere (if properly adjusted) and the bell rings. Ifthe bell is free in air it continues ringing until the knobs aregently tapped asunder; but if the bell stands on the sametable as the knobs, especially if it rests one foot on the actualstand, then its first stroke taps them back instantly and auto-matically, and so every discharge of the sending jar is * Journal Institution of Electrical Engineers, 1890, Vol. XIX., ; or Lightning Conductors and Lightning Guards, pp. 382-4. 22 SIGNALLING WITHOUT WIRES. signalled by a single stroke of the bell. Here we have inessence a system of very distinctly syntonic telegraphy, forthe jars and their circuits must b
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