Page:Jack Heaton, Wireless Operator (Collins, 1919).djvu/128

 After Hertz had shown how long electric waves could be set up by the sparks of an induction coil, other scientific chaps went to work to get up a better scheme to detect them. In 1890, of France, discovered that when metal filings were put in a tube and

electric waves were allowed to fall on them the resistance of the filings was lowered, and, in 1894, found that this was caused by the filings being drawn closer together, that is, they cohered. By connecting a coherer (see the diagram) as he called the filings detector, to a galvanometer and a dry-all