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A heliograph ((ギリシア語:Ἥλιος ''helios''), meaning "sun", and , meaning "write") is a wireless solar telegraph that signals by flashes of sunlight (generally using Morse code) reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter.〔 The heliograph was a simple but effective instrument for instantaneous optical communication over long distances during the late 19th and early 20th century.〔 Its main 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.〔 ==Description== There were many heliograph types. Most heliographs were variants of the British Army Mance Mark V version (Fig.1). It used a mirror with a small unsilvered spot in the centre. The sender aligned the heliograph to the target by looking at the reflected target in the mirror and moving his head until the target was hidden by the unsilvered spot. Keeping his head still, he then adjusted the aiming rod so its cross wires bisected the target. He then turned up the sighting vane, which covered the cross wires with a diagram of a cross, and aligned the mirror with the tangent and elevation screws so the small shadow that was the reflection of the unsilvered spot hole was on the cross target.〔 This indicated that the sunbeam was pointing at the target. The flashes were produced by a keying mechanism that tilted the mirror up a few degrees at the push of a lever at the back of the instrument. If the sun was in front of the sender, its rays were reflected directly from this mirror to the receiving station. If the sun was behind the sender, the sighting rod was replaced by a second mirror, to capture the sunlight from the main mirror and reflect it to the receiving station.〔〔(Manual Of Instruction In Army Signaling 1886 Section III- Apparatus And Method Of Using It ). Retrieved on 1 June 2008. Diagrams and instructions for British military heliograph (note British heraldry on cover).〕 The U. S. Signal Corps heliograph mirror did not tilt. This type produced flashes by a shutter mounted on a second tripod (Fig 4).〔W. N. Millar (1920), Canadian Forestry Service. (Methods of Communication Adapted to Forest Protection ) Google Books. Retrieved on 1 June 2008. pp. 160-181 are devoted to the heliograph, with diagrams of the British, American, and Godwin type.〕 The heliograph had some great advantages. It allowed long distance communication without a fixed infrastructure, though it could also be linked to make a fixed network extending for hundreds of miles, as in the fort-to-fort network used for the Geronimo campaign. It was very portable, did not require any power source, and was relatively secure since it was invisible to those not near the axis of operation, and the beam was very narrow, spreading only 50 feet per mile of range. However, anyone in the beam with the correct knowledge could intercept signals without being detected.〔〔Kipling, Rudyard (A Code of Morals ). The Kipling Society website. Retrieved on 1 June 2008.〕 In the Boer War, where both sides used heliographs, tubes were sometimes used to decrease the dispersion of the beam.〔Major J. D. Harris (WIRE AT WAR - Signals communication in the South African War 1899–1902 ). Retrieved on 1 June 2008. Discussion of heliograph use in the Boer War.〕 In some other circumstances, though, a narrow beam made it difficult to stay aligned with a moving target, as when communicating from shore to a moving ship, so the British issued a dispersing lens to broaden the heliograph beam from its natural diameter of 0.5 degrees to 15 degrees The distance that heliograph signals could be seen depended on the clarity of the sky and the size of the mirrors used. A clear line of sight was required, and since the Earth's surface is curved, the highest convenient points were used. Under ordinary conditions, a flash could be seen 30 miles (48 km) with the naked eye, and much farther with a telescope. The maximum range was considered to be 10 miles for each inch of mirror diameter. Mirrors ranged from 1.5 inches to 12 inches or more. The record distance was established by a detachment of U.S. signal sergeants by the inter-operation of stations on Mount Ellen, Utah, and Mount Uncompahgre, Colorado, 183 miles (295 km) apart on September 17, 1894, with Signal Corps heliographs carrying mirrors only 8 inches square.〔Coe, Lewis ( The Telegraph: A History of Morse's Invention and Its Predecessors in the United States ). Google Books. Retrieved on 1 June 2008.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heliograph」の詳細全文を読む スポンサード リンク
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