ca 35 __ Heliograph
‣ Comment : A Heliograph (from the Greek helios (Greek: Ἥλιος), meaning "sun", and graphein (γραφειν) = write) is a wireless solar telegraph that signals using Morse code flashes of sunlight reflected by a mirror (A device for transmitting messages by reflecting sunlight). The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter. The heliograph was a simple but highly effective instrument for instantaneous optical communication over 50 km or more in the late 19th and early 20th century. Its major uses were military, survey and forest protection work. Heliographs were standard issue in the British and Australian armies until the 1960s, and were used by the Pakistani army as late as 1975. First recorded use of mirrors to send messages by Roman Emperor Tiberius. The first recorded use of the heliograph was in 405 BC, when the Ancient Greeks used polished shields to signal in battle. In about 35 AD, the Roman emperor Tiberius, by then very unpopular, ruled his vast empire from a villa on the Isle of Capri. It is thought that he sent coded orders daily by heliograph to the mainland, eight miles away. (Compiled from various sources) — Henry Cornelius Agrippa, in a learned treatise published in Antwerp in the sixteenth century, seems to be describing the heliograph when he says that Pythagoras knew about it. The great Pharos or lighthouse at Alexandria, erected nearly three hundred years before Christ, is said by some to have had a reflecting mirror for signaling on the top of it, probably of burnished metal, for such was the material of ancient mirrors. What method of signaling did the Emperor Tiberius use in his retreat in the island of Capri, from which he ruled Rome so ably for the last ten years of his life. — what else than the heliograph ? Tacitus pictures him, an old man of more than seventy, standing on a rocky point of the island, looking towards the hills on the mainland for news of the execution of the traitor Sejanus, which he had ordered, but which might prove fatal to himself. He had a ship ready and loaded with his treasure, on which to flee if Rome turned against him. But from the hill on shore the world flashed taht all was well, and the old man turned and went back to his villa, to rule. — partly by telegraph. — for six years more. The Moors in Algeria using the heliograph, as far back as the eleven century A.D. But after ancient Rome, one hears nothing more of it in Europe for many hundreds of years. (Alvin F. Harlow)
‣ French comment : Toujours dans la gamme des procédés optiques, il y a l'héliographe, que nous avons tous utilisé, en envoyant la lumière du soleil dans l'oeil d'un camarade, en classe. L'équipement est simple, et peut être bricolé : un trépied qui supporte un miroir pouvant osciller autour d'un axe, au moyen d'un levier. On commence par régler le miroir pour que le rayon lumineux réfléchi parte dans la bonne direction, quand on actionne le levier, tandis que ce même rayon est dirigé ailleurs, quand le miroir est au repos. Il ne reste plus qu'à utiliser le code morse (les points et les traits) comme en télégraphie électrique. Cette fois, la portée peut être de plusieurs dizaines de kilomètres, et elle dépend à la fois : de la taille et de la qualité du miroir, de la transparence de l'air, de l'aide d'une jumelle ou d'une lunette du côté de la réception, de l'altitude à laquelle l'on est (plus on est haut, plus on voit loin...). Ce dispositif fut intensément utilisé pendant tout le 19ème siècle, et jusqu'au début du 20ème siècle. Certains textes grecs font déjà mention de boucliers utilisés pour faire des signaux lumineux, il y a plus de deux mille années... (Compiled from various sources)
‣ Source : Kolb, Anne (2001), “Transport and Communication in the Roman state”, In “Travel and geography in the Roman Empire”, by Colin Adams and Ray Laurence, Routledge, pp. 95-105.
‣ Source : Burns, Russell W. (2003), "Communications : An international history of the formative years", Chapter 1 / Communication among the ancients, IEEE History of Technology Series 32, pp. 192-196.
‣ Source : Harlow, Alvin F. (1936), "Old Wires and New Waves- The History of the Telegraph, Telephone and Wireless", READ BOOKS, 2008, p. 10.
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