Expérience
Marconi ouvre la voie de la transmission sans fil
Salvan - Les Marécottes
by Fred Gardiol, honorary professor at the E.P.F.L. and Yves Fournier, historian
At the end of September 1895, a gunshot rang out in the gardens of the Villa Griffone in Pontecchio, near Bologna. This detonation announced the transmission by the young Guglielmo Marconi, then aged 21, of a "wireless" message over a distance of some 2.5 kilometres. [1]. A year later, he filed patent No. 12'039/1896 in London, which was soon followed (1897) by the British Post Office's approval of a wireless transmission over a distance of 14 kilometres between Lavernock Point and Flat Holme Island in the Bristol Channel [2]. Then, in 1899, he crossed the English Channel and, in 1901, Marconi even managed to establish a transatlantic wireless link between Poldhu in England and Signal Hill in Newfoundland [3]. We all know what happened next: would it be possible today to imagine a world without radio, television or mobile phones? However, little more than anecdotal documentation remains of these early attempts to develop a reliable system.
THE FIRST TRIALS AND TRIBULATIONS OF WIRELESS TRANSMISSION
Fascinated by an article on electromagnetic waves, Guglielmo Marconi decided to transmit a message without any metallic connection between the transmitter and the receiver. In 1894, while staying in Andorno near the Santuario di Oropa in the Italian Alps, he learned of the death of Heinrich Hertz, the German physicist who had been the first to demonstrate the existence of electromagnetic waves, since then called "Hertzian waves" and predicted in 1864 by Maxwell. In a relatively short period of time, of the order of a year and a half at the most, Guglielmo Marconi gathered technical information, built apparatus in the attic of the Villa Griffone, assembled his equipment, tried to make it work and succeeded!He certainly began by repeating Hertz's experiments, then improved the performance of his apparatus to transmit through a room, along a corridor, and finally between the house and the surrounding fields. He left no notes describing the stages of his achievements [4]. Marconi had no manuals, no adequate measuring equipment, no analysis and simulation tools, and no team of specialists to call on in case of difficulty - all of which have become indispensable to today's engineer. It is therefore hardly possible to imagine the difficulties encountered by Marconi, who was only a young beginner with a rather basic education, he was rejected by the Naval Academy and the University of Bologna. However, he had an exceptional practical sense and a very strong motivation which enabled him to achieve what was at the time a real feat.
It would be very interesting to know more about how Marconi proceeded, but he apparently left us no documents describing his work during this crucial period. In fact, we have only a few oral testimonies, collected many years after the first steps of wireless technology [5]. These elements are due to Maurice Gay-Balmaz, an inhabitant of Salvan (Valais) who, one summer day in 1895, had seen a "handsome young man" equipped with strange devices arrive in his village (fig. 2).
AN OLD MAN TELLS A STORY
Born in 1885, Maurice Gay-Balmaz, still a child, was intrigued one day by "a strange device stored in the grass" not far from his house. Guglielmo Marconi, who was staying with the young Salvanin's uncle at the time, noticed the child's interest in his device and offered him to work for him, making him, without knowing it, take part in one of the greatest discoveries of our time [7].It was on the "Pierre Bergère", a boulder overlooking the village of Salvan (fig. 3), that Marconi installed his transmitter. This curious equipment included a battery, a Ruhmkorff coil, a Righi spark gap and an antenna. A few metres away, at the foot of the stone, young Maurice held a pole[1] about two and a half metres long, along which ran a metal wire connected to a "receiver" probably consisting of a Branly coheater, a battery and a bell (fig. 4), some of which had been brought from Bologna.
However, it took a long time before the signal was transmitted. Maurice Gay-Balmaz remembers the long wait: "...at first it didn't ring and then, by dint of tests, studies and adjustments to his apparatus, it rang at that distance... Marconi had a radiant face, he waved at me from the stone... he said: "It's going well, it's starting! Then he made me go further, maybe a hundred metres further. So it was a few times, ...maybe half a day of trying again before it rang. And it rang! And we went on like that" [6].
Soon the distance became too great to communicate verbally and flags were used to exchange messages. The boy waved a red flag when the bell rang, and a white flag when he heard nothing. The receiver was placed further and further away from the Pierre Bergère, the initial four or five metres soon turned into hundreds of metres, finally reaching "a property on the top of the Marécottes" at a distance of about one and a half kilometres (Fig. 5). As the reception site was not always visible from the Pierre Bergère, Maurice Gay-Balmaz had to move around to report the results of the tests. This last remark is particularly significant: at that time, it was firmly believed that - like light - electromagnetic waves propagated only in a straight line and could therefore not be received over hills or mountains; it was also thought that the curvature of the earth would limit the range of a link, but before Marconi, no one had thought of verifying this belief, which proved to be incorrect. It was therefore apparently at Salvan that a transmission without line of sight was made for the first time.
After several weeks of experimentation, Marconi returned to Italy, leaving only a few copper wires forgotten in his room in Salvan. His life then took an extremely eventful turn. On his return, he continued his experiments and confirmed the discovery of wireless telegraphy by filing a famous patent in London in 1896. From then on, he continued to improve the transmission system, thanks to which he built a veritable telecommunications empire. His discovery earned him the highest honours, including some 15 honorary doctorates and major scientific awards around the world, including the Nobel Prize in Physics in 1909. He travelled the globe tirelessly and followed the progress of his enterprises closely, both technically and commercially and financially, until a heart attack put an end to his activities in the early hours of 20 July 1937 [17].
Marconi's great merit was to have devoted his entire life to the vision he had had in 1894 and confirmed the following year in Salvan. Despite the general scepticism, he stubbornly pursued an enterprise that went against the generally accepted ideas of the time and did not let himself be discouraged by difficulties and failures. He succeeded in what many others had considered impossible. Guglielmo Marconi was a man of action, who never took the time to "look back" and write his memoirs, so that some questions will remain unanswered forever...
THE "BLURRED" NATURE OF ORAL HISTORY
From the historian's point of view, an oral testimony such as that of Maurice Gay-Balmaz remains open to question. We know that memory does not record the facts themselves, but the interpretation that the observer makes of them in the context of the moment. When, moreover, the account is given some seventy years after the events, certain inaccuracies are to be expected, and other testimonies or written documents are needed to complete and corroborate it.However, Marconi's stay in Salvan seems to be well established, not only by the testimony of Maurice Gay-Balmaz, but also by that of other inhabitants of Salvan, and his remarkably precise and detailed account describes in a plausible way how Marconi proceeded and in any case gives interesting indications of what must have happened at the time.
GENESIS OF RADIO
People often ask: who invented radio? This would require an indisputable definition of what "radio" is and what an "inventor" is, so that in the absence of clear definitions, several countries have decided that the one and only "inventor of radio" is one of their eminent citizens. Various unproductive disputes over precedence once divided the scientific world, but fortunately these have now been overcome [11, 12].The invention of radio, or rather its development, was a long adventure in which many well-known and little-known scientists participated during the 19th and 20th centuries. This epic was marked by a series of more or less significant stages. Electromagnetic radiation was first predicted by theory and then discovered experimentally. It then became apparent that this radiation could transmit messages, and the appropriate equipment was developed, eventually transmitting information over increasingly long distances that now reach the very edge of the solar system! The messages were at first very rudimentary, all-or-nothing modulated "noise" (Morse code), after which various improvements made it possible to transmit speech, music, images and, finally, computer data. New technologies appeared: semiconductor detectors, electronic tubes, transistors, integrated circuits, transmission codes, etc.
If we go back to the 'prehistory' of radio, the first player was undoubtedly the Dane Hans Christian Oersted, who showed in 1820 that an electric current could deflect the magnetic needle of a compass - the first evidence of a relationship between electricity and magnetism. A year later, the Frenchman André Marie Ampère repeated and completed the experiment, before developing a theory. Then Michael Faraday (1791-1867) discovered magnetic induction and introduced the concept of lines of force - but his status as an untrained experimenter (like Guglielmo Marconi later!) did not earn his ideas much credence until the great physicist James Clerk Maxwell used them to derive his famous equations in 1864. Maxwell's theory predicted the existence of electromagnetic radiation. All that remained was to verify its existence experimentally [2].
In the winter of 1886-1887, Heinrich Hertz - experimenting in Germany with spark generators and dipoles - succeeded in detecting the presence of electromagnetic waves and thus validated the theoretical predictions made by Maxwell in 1864. However, his equipment was not very sensitive, so that detection could only be made at a maximum of a few metres, and Hertz died in 1894 aged only 34.
In England, this work was closely followed by Oliver Lodge, who took up the torch after Hertz's death by perfecting the study of oscillating circuits. In 1893, he introduced into his receiver a filament 'coheater', recently developed in France by Edouard Branly. Branly had found that the resistance of a glass tube filled with iron filings decreased sharply in the vicinity of an electric discharge. Lodge was thus able to extend the detection distance to a few dozen metres - a distance sufficient for demonstrating to his students and at the Royal Institution. As a 'pure scientist', Lodge had never considered the practical application of his demonstrations until Alexander Muirhead, a telegraph engineer, suggested that he transmit messages, and the two men subsequently collaborated. But one of Lodge's major contributions was the presentation he made to the Royal Institution in 1894, following the death of Heinrich Hertz. This, together with a number of papers he published shortly afterwards [13], had a major impact in making work that had hitherto remained relatively confidential known throughout the world.
Lodge was thus a key figure, often unrecognised, in the development of radio. Although he had a thorough knowledge of electromagnetic radiation and much better transmission and reception equipment than the young beginner Marconi, he had little interest in applications and underestimated the potential impact of his research. Moreover, following a violent argument about the effectiveness of lightning rods, he had incurred the enmity of Sir William H. Preece, the Chief Engineer of the General Post Office, so that when the latter "took the young Marconi under his wing", any collaboration between Lodge and the new recruit became impossible. It was only much later, after the Marconi Company was forced to buy out a patent from Lodge and Muirhead, that Lodge became a sort of consultant to them.
Several other researchers had been interested in electromagnetism, obtaining more or less convincing results, which were not, however, to have such a marked impact on the development of radio [see "Precursors and Competitors"]. Although solid foundations, both theoretical and experimental, had been established, the spark of genius was still missing... this was the context in which Marconi's experiments were conducted in Salvan. A village that can today be proud of having contributed, quite unconsciously, to one of the greatest discoveries of our time by providing a particularly favourable training ground.
[1] P. Zweiacker: "Who really invented radio? Flash EPFL, 30 October 2001
[2] G.R.M. Garratt: "The Early History of Radio: from Faraday to Marconi", London, Institution of Electrical Engineers, 1994
[3] Maria Cristina Marconi, "Marconi, my beloved", Boston: Dante University of America Press, 1999
[4] N. Tesla: "On the phenomena of high-frequency vibration" (French translation), La Lumière Electrique, vol. 49, p. 340, 1893
[5] J. Cazenobe: "Did Marconi invent Radio?", La Recherche , May 1995, vol. 26, pp. 508-514
[6] P. K. Bondyopadhyay: "Marconi's 1901 transatlantic wireless communication experiment", Special session on Marconi, 31st European Microwave Conference, London, 26 September 2001
[7] I.V. Lindell: "Wireless before Marconi", IEEE APS/URSI Symposium, Boston, 2001
