Heliotrope (instrument)
{{Short description|Measuring instrument}}
{{Other uses|Heliotrope (disambiguation)}}
File:Heliotrope2-2.jpg). This may be the very one Colonna surveyed from 192 miles away.]]
File:Heliotrope Fig 1 Plate XXXVIII WBClark 1898.jpg
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.{{cite journal|url= https://books.google.com/books?id=s93bifR6Fj0C&pg=RA1-PA358 |title=The Heliotrope, a New Instrument |journal= The Gentleman's Magazine |department= Arts and Sciences |year= 1822 |page= 358 |volume= 92, Part 2 |first1= A. |last1= Dodd |first2= A. |last2= Smith }}{{cite book| last=Dunnington|first=G. Waldo|title=Carl Friedrich Gauss: Titan of Science|year=1955|publisher=Exposition Press|location=New York|isbn=0-88385-547-X|pages=122–127, 119, 221| url=http://babel.hathitrust.org/cgi/pt/search?q1=heliotrope&id=mdp.39015017285852&view=1up&seq=162}} The word "heliotrope" is taken from the Greek: helios ({{Langx|el|Ἥλιος}}), meaning "sun", and tropos ({{Langx|el|τρόπος}}), meaning "turn".
History
Heliotropes were used in surveys from {{ill|Gaussian land survey|de|Gaußsche Landesaufnahme|lt=Gauss's survey in Germany}} in 1821 through the late 1980s, when GPS measurements replaced the use of the heliotrope in long distance surveys. Colonel Sir George Everest introduced the use of heliotropes into the Great Trigonometric Survey in India around 1831,{{cite book|title=Gleanings in science, Volume 3|year=1831|publisher=Baptist Mission Press|page=344|url=https://books.google.com/books?id=5xlwAAAAIAAJ&dq=heliotrope&pg=PA344}} and the United States Coast and Geodetic Survey used heliotropes to survey the United States. The [https://archive.org/details/gov.in.is.9898.1981 Indian specification for heliotropes] was updated in 1981,{{cite book|title=Specification for Heliotrope, Surveying|year=1981|publisher=Indian Standards Institution|url=https://archive.org/details/gov.in.is.9898.1981}} and the American military specification for heliotropes (MIL-H-20194E) was retired on 8 December 1995.{{cite web|title=MIL-H-20194E Note 1|publisher=assist.dla.mil | url= https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=14150 }}
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).[http://celebrating200years.noaa.gov/theodolites/heliotrope.html Theodolites: heliotrope] at NOAA.gov
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.{{cite journal|last=Abbe|first=Cleveland|title=Meteorology and Geodesy|journal=Monthly Weather Review|date=December 1900|volume=XXVIII|issue=12|pages=545–547|url=https://books.google.com/books?id=W8NGAQAAIAAJ&dq=heliotrope+seeing&pg=PA546|accessdate=10 July 2013|doi=10.1175/1520-0493(1900)28[545:mag]2.0.co;2|doi-access=free}} 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
- Heliograph, a similar instrument, used in communication
References
{{Reflist}}
Further reading
- Silvio A. Bedini (2004): [https://web.archive.org/web/20190304054813/http://archive.amerisurv.com/PDF/TheAmericanSurveyor_BediniHeliotropes_November2004.pdf The Surveyor's Heliotrope : Its Rise and Demise]. www.TheAmericanSurveyor.com
External links
{{Commons category|Heliotrope}}
{{Wiktionary|heliotrope}}
- [http://www.amerisurv.com/PDF/TheAmericanSurveyor_BediniHeliotropes_November2004.pdf The Surveyor's Heliotrope]
- [https://archive.org/details/topographictrig00wilsgoog/page/n627 Topographic, Trigonometric and Geodetic Surveying, by Herbert Michael Wilson (1912) ] pp. 566–574 are devoted to heliotropes
- [https://archive.org/details/elementederverm00bauegoog 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.
- [http://www.surveyhistory.org/the_heliotrope1.htm The Heliotrope] A short history.
- [https://web.archive.org/web/20110722051215/http://transits.mhs.ox.ac.uk/contribute/contrib-results.php?&contributor_id=56&compiled_name=Museum%20Boerhaave&submit=yes Transits of Venus] Page with photographs of three heliotropes from 1873.
- [https://web.archive.org/web/20110518071343/http://sill-www.army.mil/FAMAG/1969/NOV_1969/NOV_1969_PAGES_73_75.pdf Improvised Heliotrope] this 1969 article also provides the US Army part number for a heliotrope.
- [http://celebrating200years.noaa.gov/theodolites/heliotrope.html Heliotrope] Heliotrope photo, description of a 192-mile record.