Signalling through space without wires : being a description of the work of Hertz & his successors . essary to connect the column for the poles of a 25 cell battery, for the resistance originallyinfinite to be reduced to 4,000 ohms. 102 SIGNALLING WITHOUT WIRES. The arrangement shown in Fig, 56 illustrates another orderof experiment. Two rods of copper were oxidised in the flameof a Bunsen burner, and were then arranged to lie acrosseach ether, as shown, and were connected to the terminals ofthe arm of a Wheatstone bridge, the high resistance of thecircuit being due to the layers of o
Signalling through space without wires : being a description of the work of Hertz & his successors . essary to connect the column for the poles of a 25 cell battery, for the resistance originallyinfinite to be reduced to 4,000 ohms. 102 SIGNALLING WITHOUT WIRES. The arrangement shown in Fig, 56 illustrates another orderof experiment. Two rods of copper were oxidised in the flameof a Bunsen burner, and were then arranged to lie acrosseach ether, as shown, and were connected to the terminals ofthe arm of a Wheatstone bridge, the high resistance of thecircuit being due to the layers of oxide. Amongst the manymeasurements made, I found, in one case, a resistance of80,000 ohms, which, after exposure to the influence of theelectric spark, was reduced to 7 ohms. Analogous effects areobtained with oxidised steel rods. Another pretty experimentis to place a cylinder of copper, with an oxidised hemisphericalhead, on a sheet of oxidised copper. Before exposure to theinfluence of the electric spark, the oxide offers considerableresistance. The experiment can be repeated several times by. Fig. 56. merely moving the cylinder from one place to another on theoxidised sheet of copper, thus showing that the phenomenononly takes place at the point of contact of the two layers ofoxide. In conclusion, it may be worth noting that, for most of thesubstances enumerated, an elevation of temperature diminishesthe resistance, but the effect of a rise of temperature is transient,and is incomparably less than the effect due to currents of highpotential. For a few substances the two effects are opposed. A second article by Mr. Branly in La Lumiere Electriquewas abstracted in The Electrician for August 21, 1891, asfollows:— In a preceding article I showed that certain substancesundergo an increase in conductivity under various electrical BRANLTS EXPERIMENTS. 103 influences, and that these substances are numerous. Theincrease in conductivity varies with the energy of the excitingsource.
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