Milestones:Discovery of Radioconduction by Edouard Branly, 1890

Discovery of Radioconduction by Edouard Branly, 1890

In this building, Edouard Branly discovered radioconduction, now called the Branly Effect. On 24 November 1890, he observed that an electromagnetic wave changes the ability of metal filings to conduct electricity. Branly used his discovery to make a very sensitive detector called a coherer, improved versions of which became the first practical wireless signal receivers.

The plaque may be viewed at 21 rue d'Assas, 75006, Paris, France on the wall of the building of the “Institut Catholique de Paris” (a renowned catholic university founded by Ozanam and Cauchy)), which housed, in Particular, ISEP, a School of Engineering linked with Stanford University. In this very place, Edouard Branly discovered the radioconduction on November 24th 1890.

The discovery of the radioconduction is a phenomenon which revolutionized the means of communication. It is at the origin of the development of the TSF (Télégraphie Sans Fil, or wireless telegraphy). As a member of the French Academy of Sciences (it gains vis-a-vis Marie Curie), Branly received international recognition. No more than about fifteen years separate the first wireless transmission across a few meters (1890) from the first transatlantic communication (Marconi, December 1901). Radioconduction (Branly’s effect) is still the subject of research, it was partially interpreted by Bernard Castaing (member of the Academy of Science of Paris) in 2006.

The “filings tube” (or coherer) was the first widely used detector for radio communication. The operation of the coherer is based upon the large resistance offered to the passage of electric current by loose metal filings, which decreases under the influence of radio frequency. The coherer became the basis for radio reception, and remained in widespread use for about ten years. It was used by, amongst others, Guglielmo Marconi, in his early experiments. Oliver Lodge adds a "trembler" which periodically dislodged clumped filings, thus restoring the device's sensitivity. The “coheror” was used not only during the first phase of development of the wireless telegraphy, but it was also used by Christian Hülsmeyer as a receiver of his Telemobiloskop, the first radar (1904).

The discovery of electromagnetic waves had been made by Heinrich Hertz in 1888, but the “detector” he used (a simple loop) was very ineffective, while a “coheror” was able to detect even a faint signal. Furthermore the “coheror” was able to be directly linked to a Morse’s system, and though it was able to be used in a wireless communication. Edouard Branly is one of the pioneer of wireless transmission along with Heinrich Hertz, Oliver Lodge and Guglielmo Marconi.

Heinrich Rudolf Hertz (1857-1894), a professor of physics at Karlsruhe Polytechnic, was the first to broadcast and receive radio waves in the laboratory. Between 1885 and 1889, he used spark discharges to produce electromagnetic waves. His receiver was a loop of wire with a small gap across which a small spark could be observed when the radiator discharged. Hertz died suddenly when he was thirty six, perhaps never realizing that transmission and reception over long distances was possible.

Edouard Eugène Désiré Branly (1844-1940) is at the origin of wireless telegraphy. In 1890, Branly, a professor of Physics at the Catholic University of Paris, discovered that when exposed to even a distant spark transmission field, loose zinc and silver filings would “cohere” and provide a path of increased conductivity that could be used to detect the presence of the transmission. The "coherer" took radio transmission out of the laboratory and made communication over long distances possible.

Oliver Joseph Lodge (1851-1940) held the chair in Physics at the University College in Liverpool when he demonstrated a practical form of the Branly coherer in 1894. Lodge added a device that shook the filings loose between spark receptions. It became a standard device in early wireless telegraphy. Lodge also obtained the first patents for the use of tuned circuits to adjust the frequency of receivers and transmitters.

Guglielmo Marconi (1874-1937) In 1896, at age twenty-two, he patented a successful system of radio telegraphy. In the following years he introduced a notable series of inventions and ingenious redesigns of transmitting and receiving system components. In 1901 Marconi succeeded in receiving signals transmitted across the Atlantic Ocean. Marconi's Wireless Telegraphy Company soon established a net of coast stations in Britain for ship-to-shore communication. These were taken over by the British General Post Office in 1910, but for more than a decade the Marconi Company enjoyed a monopoly on maritime radio equipment sales by virtue of an agreement with Lloyds of London to only insure ships that used their equipment. In 1909 Marconi received the Nobel Prize for Physics.

During the first trans channel wireless transmission, Marconi sent the following telegram to Branly : “Mr. Marconi sends to Mr. Branly his respectful compliments for the wireless telegraphy through the English Channel. This beautiful result being due partly to remarkable work of Mr. Branly.”

One of the most famous street in Paris is Quai Edouard Branly (a road that runs alongside the River Seine along the Eiffel Tower. It is the name of this road, not of Branly himself, that led to the naming of the Musée du quai Branly). There are a lot of streets “Edouard Branly” in France

A museum is dedicated to his achievements : Musée Branly, see : http://www.museebranly.isep.fr/

There is a memorial dedicated to Edouard Branly in the Jardin du Luxembourg (at ~ 500 m of the Institut Catholique de Paris where the milestone plaque is fixed)

A specific association exists since 1978 : Association des amis d’Edouard Branly (web site will open end of May 2008)

Prix Branly (Branly’s Prize) is given each year on November 24th since 1990 under the auspice of the “Association des amis d’Edouard Branly”

A school of Engineering was name after him (“Ecole Branly”, now Institut Supérieur d’Electronique de Paris, ISEP). Several “Lycée Branly” exist in France.

Some reference book on this subject

Edouard Branly et la T.S.F, Gabriel Pelletier et Jean Quinet, Ed. Seghers, collection "Savants du monde entier" (1962) [Gabriel Pelletier was the assistant of Edouard Branly]
Branly au temps des ondes et des limailles, Philippe Monod-Broca (afterword of Jean Cazenobe), Ed. Belin, collection "Un savant, une époque" (1999)
Musée Branly, appareils et matériaux d’expériences, Association des amis d’Edouard Branly, catalogue of the Museum, supported by Richard Loundsbery Fundation.
Comment Branly a découvert la radio, Jean-Claude Boudenot (Nominator of the Milestone) Ed. EdP Sciences (2005)

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