Edouard Branly, the Coherer, and the Branly effect [History of Communications

Abstract

Critical to the success of Marconi's pioneering work on radio telegraphy was the device needed to detect the radio telegraph messages on reception. Marconi finally settled on the "coherer." The invention of the device is often attributed to Oliver Lodge, a British physicist of the late 19th century. The detection properties of this device were, in fact, discovered by Edouard Branly, a French experimental physicist of the same period. As Dr. Dilhac makes clear in the following, Lodge himself attributed the signal detection properties of the coherer to Branly, coining the term coherer, and calling the device the "Branly coherer." The article clearly and succinctly discusses Branly's life, and describes the circumstances around which the coherer detection property was discovered by Branly. As pointed out by Dr. Dilhac, the physics behind the coherer long eluded scientists, and is just now, hopefully, becoming understood. During his life, Branly constantly denied being the inventor of radio, claiming that as a scientist he had only discovered an effect that had permitted others, like Popov, to develop wireless transmission. On the other hand, he was one of the earliest promoters of the remote control of equipment. During a largely publicized demonstration on 30 June 1905 at Palais de Chaillot in Paris he demonstrated the possibility to remotely and wirelessly turn light bulbs on and off or activate various electromechanical apparatus including motors. He made a publication on that topic in Compte-rendus a l'Academie des Sciences de Paris in March 1905. What is today called the Branly effect refers to a set of phenomena some of which were discovered before Branly. However, Branly was undoubtedly the first to publish about the effect of a spark that is, in modern words, the effect of an electromagnetic wave. Therefore, through the coherer and the demonstration that radio waves could easily be detected over long distances, he permitted early developments in wireless telecommunications. Finally and surprisingly, because of both its own intrinsic complexity and its potential involvement in modern technology, the Branly effect is today still a subject of investigation.