Text: A device formerly employed for detecting radio waves. In its original form it consisted of two metal rods separated by a narrow space in a glass tube and the gap between the rods filled with nickel and silver filings. It was found that when the electromagnetic waves or signals were passed through the coherer the particles of filings clung together and became conductors. Then by using some device such as the tapper hammer of an electric bell to strike the glass tube, again separating the particles after each signal, it was possible to keep the coherer constantly in a state of change between a conductive and a non-conductive condition, thus making the signals audible. There were many variations of this type of detector, which, however, is now obsolete.

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Source: 190