Heliotrope (instrument)
The heliotrope is an instrument that uses a mirror to reflect sunlight over great distances to mark the positions of participants in a land survey. The heliotrope was invented in 1821 by the German mathematician Carl Friedrich Gauss.[1][2] The word "heliotrope" is taken from the Greek: helios (Greek: Ἥλιος), meaning "sun", and tropos (Greek: τρόπος), meaning "turn".
History
[edit]Heliotropes were used in surveys from Gauss's survey in GermanyColonel Sir George Everest introduced the use of heliotropes into the Great Trigonometric Survey in India around 1831,[3] and the United States Coast and Geodetic Survey used heliotropes to survey the United States. The Indian specification for heliotropes was updated in 1981,[4] and the American military specification for heliotropes (MIL-H-20194E) was retired on 8 December 1995.[5]
in 1821 through the late 1980s, when GPS measurements replaced the use of the heliotrope in long distance surveys.Surveyors used the heliotrope as a specialized form of survey target; it was employed during large triangulation surveys where, because of the great distance between stations (usually twenty miles or more), a regular target would be indistinct or invisible. Heliotropes were often used as survey targets at ranges of over 100 miles. In California, in 1878, a heliotrope on Mount Saint Helena was surveyed by B. A. Colonna of the United States Coast and Geodetic Survey from Mount Shasta, a distance of 192 miles (309 km).[6]
The heliotrope was limited to use on sunny days and was further limited (in regions of high temperatures) to mornings and afternoons when atmospheric aberration least affected the instrument-man's line of sight.[7] The heliotrope operator was called a "heliotroper" or "flasher" and would sometimes employ a second mirror for communicating with the instrument station through heliography, a signalling system using impulsed reflecting surfaces. The inventor of the heliograph, a similar instrument specialized for signaling, was inspired by observing the use of heliotropes in the survey of India.
See also
[edit]- Heliograph, a similar instrument, used in communication
References
[edit]- ^ Dodd, A.; Smith, A. (1822). "The Heliotrope, a New Instrument". Arts and Sciences. The Gentleman's Magazine. 92, Part 2: 358.
- ^ Dunnington, G. Waldo (1955). Carl Friedrich Gauss: Titan of Science. New York: Exposition Press. pp. 122–127, 119, 221. ISBN 0-88385-547-X.
- ^ Gleanings in science, Volume 3. Baptist Mission Press. 1831. p. 344.
- ^ Specification for Heliotrope, Surveying. Indian Standards Institution. 1981.
- ^ "MIL-H-20194E Note 1". assist.dla.mil.
- ^ Theodolites: heliotrope at NOAA.gov
- ^ Abbe, Cleveland (December 1900). "Meteorology and Geodesy". Monthly Weather Review. XXVIII (12): 545–547. doi:10.1175/1520-0493(1900)28[545:mag]2.0.co;2. Retrieved 10 July 2013.
Further reading
[edit]- Silvio A. Bedini (2004): The Surveyor's Heliotrope : Its Rise and Demise. www.TheAmericanSurveyor.com
External links
[edit]- The Surveyor's Heliotrope
- Topographic, Trigonometric and Geodetic Surveying, by Herbert Michael Wilson (1912) pp. 566–574 are devoted to heliotropes
- Elemente der Vermessungskunde, (in German) by Karl Maximilian von Bauernfeind (1862) pp. 115–122 are devoted to Gauss's heliotrope, and the Stierlin and Steinheil heliotropes are described as well.
- The Heliotrope A short history.
- Transits of Venus Page with photographs of three heliotropes from 1873.
- Improvised Heliotrope this 1969 article also provides the US Army part number for a heliotrope.
- Heliotrope Heliotrope photo, description of a 192-mile record.
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