A D V E N T U R E S   in   C Y B E R S O U N D

In 1890, a French inventor, Edouard Eugène Désiré Branly, Physics professor at the Catholic University of Paris, created a tube containing loose zinc and silver filings, with contact plugs on each end. The shavings would stick together after the first spark transmission was received; a method* of separating them for the next signal was necessary.

* The Russian 'Father of Wireless' Alexander Popov also came up with the idea of using a vibrator and the hammer of an electric bell to strike the tube and cause the filings to separate.

Source: B. Eric Rhoads

Although little known abroad, Edouard Eugène Désiré Branly is considered in France as being the inventor of wireless telegraphy, and his name is a symbol of the alliance of science and technology. The history of the early stages of wireless telegraphy illustrates the complexity of relations between scientific research, technical invention and the industrial and commercial development of a new product.

Branly, a physics professor at the Catholic Institute in Paris, first encountered telegraphy indirectly via the intermediary of one of his professors at the Sorbonne, Paul Desains, who had made attempts at telegraphy using underwater or terrestrial means. However, his experiments never achieved distances long enough to rival traditional telegraphy.

In 1890, Dr. Branly became passionately interested in another field of application for electricity : electrotherapy. In the morning, he would go to the Salpêtrière or Hôtel-Dieu hospitals in Paris, where he subjected patients' bodies to electric shocks, luminous discharges and induced currents. In the afternoon, it was the turn of metallic conductors and galvanometers to be charged with electricity in his physics laboratory.

However, the device which made Branly famous, the "filings tube", more generally known as a "coherer", is a very special sort of conductor. It consists in a glass tube filled with metal filings which acts as an insulator when placed in a circuit comprising a battery and a galvanometer. However, if an electric spark is created some distance away, it becomes a conductor and lets the current pass into the circuit. When the tube is tapped lightly, it becomes an insulator again and interrupts the current. This phenomenon was described by Branly in 1890 further to research carried out on the photoelectric effect.

At that time, although the action of the spark on the tube could be observed across the walls of his laboratory and over a distance of up to twenty metres, Branly never dreamed of the possibility of transmitting signals by this means. He was mainly concerned with establishing a parallel between medicine and physics, and was to offer the medical world an interpretation of nerve conductivity based on the model of the conductivity of filings tubes.

The physicist Heinrich Hertz, who was experimenting in Germany on waves with a very short wavelength, did not believe in the possibility of propagating electromagnetic waves beyond the small area of his laboratory, unlike another physicist, William Crookes, who evoked the possibility of long-distance communication using this new method in 1892.

It was the British physicist Oliver Lodge who was to publicly demonstrate the link between the filings tube and electromagnetic waves. Having long been convinced of the existence of such waves, he attempted to highlight their presence in closed circuits and soon succeeded in reproducing, varying and interpreting his experiments.

On the death of Hertz, whom he had known well, he took Branly's tube, added a hammer* which hit it automatically every time the spark was detected and, to make his demonstration even more instructive, added either a bell or an underwater telegraphy device to the receiving circuit. Lodge thus visibly demonstrated the physical properties of waves without being able to propose further technical developments which could meet a practical demand. Like Branly, he was extremely interested in the links between physiology and electricity and was an active member of a Society for Psychic Research, which led him into research areas far removed from a wireless telegraphy project.

Theoretically speaking, all the key elements required for a system of transmission via electromagnetic waves were by this time in existence : Hertz' spark gap transmitter, a receiver with a filings tube and the principles of frequency tuning between the transmitting circuit and the receiving circuit. These were worked on by a number of experimenters.

However, it was Marconi who, in an attempt to increase the distance between the transmitter and the receiver, gradually modified the spark gap and the coherer, and aimed one end of the transmitting circuit towards the sky while attaching the other to the earth. After his first remarkable achievements, Marconi submitted the first in a long series of patents in March 1897.

Marconi was undoubtedly an inventor, an organizer and an astute businessman; but Branly and Lodge were not only professors limited to the quest for knowledge within their particular discipline. Lodge founded a Wireless Telegraphy Society, while Branly was a member of the first "TSF" (Wireless Telegraphy) Society before working with other physicists on improving the coherer, which continued to take the form of a spark transmitted wave detector until around 1910.

Source: http://www.cnam.fr/museum/Revue/Revue12/Revue12-1VA.html

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