"Applications of science to warfare and materialistic enjoyment mil be the downfall of mankind^
Edouard Branly
The science behind the coherer had long been observed by various people before anybody actually managed to put it to any practical use. The effects of electrical charge on small specks of certain matter,' such as dust, was noted in around 1850 by a man named Guitard. He spotted that when dusty air was electrified, the particles of dust would gather together to form a sort of stringed formation. It was not until 1890 that Edouard Branly (1844-1940) found a way for this unusual phenomenon to be exploited.
Experimenting with thin pieces of platinum film on glass, Branly discovered that there was a massive variation in the film's electrical resistance when it was subjected to electromagnetic waves (known at the time as Hertzian waves, known today more commonly as radio waves). This discovery led Branly to create the coherer—a piece of equipment that consists of little more than a few metal filings lying loosely between two metallic electrodes in a glass tube. In its normal state, the coherer has a huge resistance. In the presence of Hertzian waves, the filings allow current to pass through them. Connected to a circuit, the coherer can then be used to detect electromagnetic signals.
This device became the basis of radiotelegraphy and was used in the development of wireless telegraphy, most notably by Marconi.
