English: A coherer, a primitive radio wave detector used in the first radio receivers around the turn of the 20th century. This type was developed by Guglielmo Marconi in the late 1890s. It consists of a tube or capsule containing two electrodes spaced a small distance apart, with metal filings in the space between them. When a radio frequency signal is applied to the device, the initial high resistance of the filings reduces, allowing an electric current to flow through it.