Signalling through space without wires : being a description of the work of Hertz & his successors . st the spark increases the conductivity; in fact, withcertain substances successive sparks produce successive jerks,and a gradually increasing and persistent deflection of thegalvanometer. Influence of a Conductor traversed by Condenser Discharges.—While using a Wimshurst machine it was noticed that thereduction in the resistance of the filings frequently took place BRANLTS EXPERIMENTS. 97 before discharge. This led me to the following experiment:Take a long brass tube, one en
Signalling through space without wires : being a description of the work of Hertz & his successors . st the spark increases the conductivity; in fact, withcertain substances successive sparks produce successive jerks,and a gradually increasing and persistent deflection of thegalvanometer. Influence of a Conductor traversed by Condenser Discharges.—While using a Wimshurst machine it was noticed that thereduction in the resistance of the filings frequently took place BRANLTS EXPERIMENTS. 97 before discharge. This led me to the following experiment:Take a long brass tube, one end of which is close to thecircuit containing the metallic powder ; its other end, severalmetres distant from the circuit, is fairly close to a chargedLeyden jar. A spark takes place and the conductor is the same instant, the conductivity of the metallic powderis greatly increased. The following arrangement, owing to its efficacy, con-venience, and regularity of action was used by me in most ofmy researches, and I shall briefly call it the A arrangement(see Fig. 53). ^3; A K Fra. The source of electricity is a two-plate Holtz machinedriven at from 100 to 400 revolutions. A sensitive substanceis introduced into one of the arms of a Wheatstone bridge, orinto the circuit of a single Daniell cell at a distance of some10 metres (34ft.) from the Holtz machine. Between thedischarge knobs of the machine and the Wheatstone bridge,and connected to the former, there are two insulated brasstubes, A A, running parallel to one another 40 centimetresapart. The Leyden jars usually attached to a Holtz machinemay be dispensed with, the capacity of the long brass tubesbeing in some measure equivalent to them. The knobs Swere 1mm., 5mm., or 1mm. apart. When the plates wererotated sparks rapidly succeeded each other. Experimentsshowed that these sparks had no direct effect at a distance of10 metres. The two tubes A A are not absolutely necessary, h. 98 SIGNALLING WITHOUT WIRES. the
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