Coherer
From ETHW
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Paris, France. On 24 November 1890, Édouard Branly invented the Coherer, a device important in the early development of wireless telegraphy. The device, a glass tube with terminals containing metal filings, acts as an insulator unless acted upon by an electric spark, when it becomes a conductor. Tapping the device separates the filings and it again becomes an insulator.
