Heliotrope Fig 1 Plate XXXVIII WBClark 1898

The heliotrope is an instrument that uses a

mirror A mirror or looking glass is an object that Reflection (physics), reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the ...

to reflect

sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight whe ...

over great distances to mark the positions of participants in a land survey. The heliotrope was invented in 1821 by the German

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History ...

Carl Friedrich Gauss Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...

. The word "heliotrope" is taken from the Greek: ''

helios In ancient Greek religion and mythology, Helios (; grc, , , Sun; Homeric Greek: ) is the god and personification of the Sun (Solar deity). His name is also Latinized as Helius, and he is often given the epithets Hyperion ("the one above") ...

'' (), meaning "sun", and '' tropos'' (), meaning "turn". Heliotropes were used in surveys from 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 The Great Trigonometrical Survey was a project that aimed to survey the entire Indian subcontinent with scientific precision. It was begun in 1802 by the British infantry officer William Lambton, under the auspices of the East India Company ...

in India around 1831, and the US Coast and Geographic Survey used heliotropes to survey the United States. Th
Indian specification for heliotropes
was updated in 1981, and the American military specification for heliotropes (MIL-H-20194E) was retired on 8 December 1995.

Surveyors Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is c ...

used the heliotrope as a specialized form of survey target; it was employed during large

triangulation In trigonometry and geometry, triangulation is the process of determining the location of a point by forming triangles to the point from known points. Applications In surveying Specifically in surveying, triangulation involves only angle me ...

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 Mount Saint Helena (Wappo: Kanamota, "Human Mountain") is a peak in the Mayacamas Mountains with flanks in Napa, Sonoma, and Lake counties of California. Composed of uplifted 2.4-million-year-old volcanic rocks from the Clear Lake Volcanic F ...

was surveyed by B.A. Colonna of the USCGS from

Mount Shasta Mount Shasta ( Shasta: ''Waka-nunee-Tuki-wuki''; Karuk: ''Úytaahkoo'') is a potentially active volcano at the southern end of the Cascade Range in Siskiyou County, California. At an elevation of , it is the second-highest peak in the Cascades ...

, a distance of 192 miles (309 km).Theodolites: heliotrope
at

NOAA The National Oceanic and Atmospheric Administration (abbreviated as NOAA ) is an United States scientific and regulatory agency within the United States Department of Commerce that forecasts weather, monitors oceanic and atmospheric conditio ...

.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. 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 heliograph () is a semaphore system 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 heliograp ...

, a similar instrument specialized for signaling, was inspired by observing the use of heliotropes in the survey of

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

References

External links

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.

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 photo, description of a 192-mile record. {{clear Surveying instruments Carl Friedrich Gauss

See also

References

External links