AskDefine | Define heliograph

Dictionary Definition

heliograph n : an apparatus for sending telegraphic messages by using a mirror to turn the sun's rays off and on v : signal by means of a mirror and the using the sun's rays

User Contributed Dictionary

English

Noun

  1. An apparatus for signalling by means of a moveable mirror which reflects flashes of sunlight.
  2. A heliogram.
  3. An instrument for measuring the intensity of sunlight.
  4. A device for photographing the sun.
  5. A photograph.

Verb

  1. To send a message by heliograph.
  2. To send a heliograph.

Extensive Definition

this the signalling device A Heliograph (from the Greek words helios = sun and graphein (γραφειν) = write) is a wireless solar telegraph that signals using Morse code flashes of sunlight reflected by a mirror. The flashes are produced by interrupting the beam with a shutter, or pivoting the mirror. The heliograph was a simple but highly effective instrument for instantaneous optical communication over 100km or more in the late 19th and early 20th century. Its major uses were military, survey and forest protection work. It was used by the Pakistani army as late as 1975. If the sun was in front of the sender, its rays were reflected directly from a mirror to the receiving station. The sender used the sighting rod to align the flash with the receiver. If the sun was behind the sender, its rays were reflected from one mirror to another, to send the beam on to the target receiver. The British army version had a single mirror with a small sighting hole in the middle and a keying mechanisms that tilted the mirror up a few degrees at the push of a lever at the back of the instrument. Auxiliary mirrors mounted on separate tripods were used to redirect the sunlight if it were not coming from a favorable angle.
The heliograph had some powerful advantages. It allowed long distance communication without a fixed infrastructure, though it could also be linked to make a fixed network extending over hundreds of miles, as in the fort-to-fort network used in the Geronimo campaign. It was highly portable, required no power source, and was relatively secure since it was invisible to those not near the axis of operation. However, anyone in the beam with the correct knowledge could intercept signals without being detected.
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 Sept 17, 1894, with Signal Corps heliographs carrying mirrors only 8 inches square.

History

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.
The German professor Carl Friedrich Gauss, of Georg-August University of Göttingen, outlined a first design for a predecessor of the heliograph (called heliotrope) in 1810. His device directed a controlled beam of sunlight to a distant station to serve as a marker for geodetic survey work.
Sir Henry Christopher Mance (1840-1926), of British Army Signal Corps, developed the first apparatus while stationed at Karachi, Bombay. Coe was familiar with heliotropes through their use in the Great India Survey.
The simple and effective instrument that Mance invented was to be an important part of military communications for the next 40 years. Limited to use in sunlight, the heliograph became the most efficient visual signalling device ever known. In pre-radio days it was often the only means of communication that could span ranges of up to 100 miles with a lightweight portable instrument. In 1889 the U.S. Signal Service reviewed all of these devices, as well as the Finley Helio-Telegraph
The last great use of the heliograph was during the Boer War in South Africa, and was used by both sides.
The heliograph remained standard equipment for military signallers in the Australian and British armies until the 1960s, where it was considered a "low probability of intercept" form of communication. Canada was the last major army to keep the heliograph as an issue item. By the time the mirror instruments were retired they were seldom used for signalling. Still, the army hated to see them go as "They made damn fine shaving mirrors."
  • In the book "The War of the Worlds", by H.G. Wells (1898) heliographs are used to convey information about the invading Martians.
  • The short story "The Attack on the Mountain", by Glendon Swarthout, in the Saturday Evening Post Magazine, July 4, 1959, described the use of the heliograph in the American West.
  • The 2004 Western novel "The Sergeant's Lady", by Miles Hood Swarthout, is set against the background of the heliograph network used in the U.S. Army campaign against the Apache Indians
heliograph in German: Heliograph (Nachrichtenübertragung)
heliograph in Esperanto: Heliografo
heliograph in Interlingua (International Auxiliary Language Association): Heliographo (telecommunication)
heliograph in Dutch: Heliograaf
heliograph in Slovak: Heliograf (signalizačný prístroj)
heliograph in Swedish: Heliograf
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