. An elementary book on electricity and magnetism and their applications. d many others, we must conclude thatan oscillatory discharge or spark sends out waves in the sur-rounding ether. The ether does for the electric circuits whatthe rubber tubing did for the pendulums. It serves as amedium for the transfer of energy. Since these electric waveswere first detected and measured by Hertz, they are calledHertzian waves. 373. Electric-wave detectors. In order to utilize the effectsof the Hertzian waves at any great distance it was necessaryto invent a detector of highsensitiveness. One means, in-
. An elementary book on electricity and magnetism and their applications. d many others, we must conclude thatan oscillatory discharge or spark sends out waves in the sur-rounding ether. The ether does for the electric circuits whatthe rubber tubing did for the pendulums. It serves as amedium for the transfer of energy. Since these electric waveswere first detected and measured by Hertz, they are calledHertzian waves. 373. Electric-wave detectors. In order to utilize the effectsof the Hertzian waves at any great distance it was necessaryto invent a detector of highsensitiveness. One means, in-vented by Branly and used byMarconi in his first wirelesstelegraphs, is called a consists of a small glass tubeclosed at each end by metal . , /T^. , ~ ~N A c Fig. 400. — Coherer, an early form pistons (Fig. 400). A space of of wave detector. a millimeter or two between the pistons at A is filled with rather coarse filings of nickel and silver. When electric waves fall on this coherer, the mass of filings coheres or sticks together and becomes a 550 ELECTRICITY AND MAGNETISM
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