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 by the German mathematician Carl Friedrich Gauss. [ [http://books.google.com/books?id=s93bifR6Fj0C&pg=RA1-PA358&lpg=RA1-PA358&dq=heliotrope+inventor&source=web&ots=b33mPoQ75X&sig=VctfyuoSbOpp4GrgVETKpl4hLFw&hl=en&sa=X&oi=book_result&resnum=4&ct=result#PRA1-PA358,M1 The Heliotrope, a New Instrument - Arts and Sciences - The Gentleman's Magazine] ] The word "heliotrope" is taken from the Greek: "helios" (Lang-el| Ἥλιος), meaning "sun", and "tropos" (Lang-el|τροπή), meaning "turn". It is a fitting name for an instrument which can be turned to reflect the sun toward a given point.

The heliotrope was utilized by surveyors as a specialized form of 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 appear indistinct. Heliotropes have been used repeatedly 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 USCGS from Mount Shasta, a distance of 192 miles (309km) [ [http://celebrating200years.noaa.gov/theodolites/heliotrope.html NOAA 200th: Collections: Theodolites: heliotrope] ]

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 did not affect the instrument-man's line of sight. 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.

References

See also

* Heliograph, a similar instrument, used in communication

External References

* [http://www.amerisurv.com/PDF/TheAmericanSurveyor_BediniHeliotropes_November2004.pdf The Surveyor's Heliotrope]
* [http://books.google.com/books?id=3SEJAAAAIAAJ&pg=RA1-PA569&lpg=RA1-PA569&dq=heliotrope+mirror+surveying&source=web&ots=VrrlXxVead&sig=EU0waoBEpG6iy7xLgDdsl2UtSLs&hl=en Topographic, Trigonometric and Geodetic Surveying, by Herbert Michael Wilson (1912) ] pp. 566-574 are devoted to heliotropes
* [http://books.google.com/books?id=Xv0IAAAAIAAJ 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.
* [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.
* [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 192 mile record.