.gif)
Heliotrope (instrument)
Encyclopedia
Mirror
A mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
to reflect sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
over great distances to mark the positions of participants in a land survey
Surveying
See Also: Public Land Survey SystemSurveying or land surveying is the technique, profession, and science of accurately determining the terrestrial or three-dimensional position of points and the distances and angles between them...
. The heliotrope was invented by the German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
mathematician
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
Carl Friedrich Gauss
Carl Friedrich Gauss
Johann Carl Friedrich Gauss was a German mathematician and scientist who contributed significantly to many fields, including number theory, statistics, analysis, differential geometry, geodesy, geophysics, electrostatics, astronomy and optics.Sometimes referred to as the Princeps mathematicorum...
.
The word "heliotrope" is taken from the Greek: helios
Helios
Helios was the personification of the Sun in Greek mythology. Homer often calls him simply Titan or Hyperion, while Hesiod and the Homeric Hymn separate him as a son of the Titans Hyperion and Theia or Euryphaessa and brother of the goddesses Selene, the moon, and Eos, the dawn...
, meaning "sun", and tropos , 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
Triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...
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
Mount Saint Helena
Mount Saint Helena 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 Field, it is one of the few mountains in the San Francisco Bay Area to receive any snowfall...
was surveyed by B.A. Colonna of the USCGS
U.S. National Geodetic Survey
National Geodetic Survey, formerly called the U.S. Coast and Geodetic Survey , is a United States federal agency that defines and manages a national coordinate system, providing the foundation for transportation and communication; mapping and charting; and a large number of applications of science...
from Mount Shasta
Mount Shasta
Mount Shasta is located at the southern end of the Cascade Range in Siskiyou County, California and at is the second highest peak in the Cascades and the fifth highest in California...
, a distance of 192 miles (309km).
Aberration in optical systems
Aberrations are departures of the performance of an optical system from the predictions of paraxial optics. Aberration leads to blurring of the image produced by an image-forming optical system. It occurs when light from one point of an object after transmission through the system does not converge...
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
Heliography
Heliography is the photographic process invented by Joseph Nicéphore Niépce around 1822, which he used to make the earliest known permanent photograph from nature, View from the Window at Le Gras . The process used bitumen , as a coating on glass or metal, which hardened in relation to exposure to...
, a signalling system using impulsed reflecting surfaces. The inventor of the Heliograph
Heliograph
A heliograph is a wireless solar telegraph that signals by flashes of sunlight reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter...
, a similar instrument specialized for signaling, was inspired by observing the use of heliotropes in the survey of India.
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.
- 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.