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TIMELINE: Surveying Instruments

Neha Arora
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Surveying is believed to be the third oldest profession in the world. To a surveyors, the link chain symbolises a rugged era, in terms of evolution of surveying technology and equipments. The chain was a precision part of a surveyor’s equipment for years. Then the Renaissance in education and scientific knowledge provided the necessary intellectual foundation for the development of modern surveying.

With the advent of the electronic distance meter, GPS, GIS, and computer-controlled Land Surveying, the profession of surveyors has turned from a labor-intensive type into a more sedate one.

A brief chronology of surveying instruments provided here, traces the history of surveying:
Around 1400 B.C., the Egyptians first used the predecessors of modern surveying instruments to accurately divide land into plots for the purpose of taxation and to engineer many feats, from canals to pyramids. An ancient Egyptian survey crew used measuring ropes, plumb bobs, sighting instruments, and leveling instruments. The ancient Egyptian measuring rope was stretched taut between stakes and then rubbed with a mixture of beeswax and resin. Some of the ropes depicted in hieroglyph were graduated by knots tied at intervals.

Image courtesy: www.surveyhistory.org/images/egyptian.JPG

Diopter
Around 120 B.C., Greeks developed the science of geometry and were using it for precise land division. Greeks developed the first piece of surveying equipment (Diopter). In a work entitled Diopter, Hero of Alexandria, describes it as a portable instrument, an application of the cogwheel, screw, and water level, for taking terrestrial and astronomical measurements. Because of some similarities, Hero’s diopter is usually recognized as the ancestor of the modern theodolite.

Image courtesy:

Magnetic Compass
The magnetic compass is an old Chinese invention, probably first made in China during the Qin dynasty (221-206 B.C.) Lodestones (a mineral composed of an iron oxide which aligns itself in a north-south direction) turned out to be better at pointing out real directions, leading to the first compasses. They designed the compass on a square slab which had markings for the cardinal points and the constellations. The pointing needle was a lodestone spoon-shaped device, with a handle that would always point south. Magnetized needles used as direction pointers instead of the spoon-shaped lodestones appeared in the 8th century AD, again in China, and between 850 and 1050 they seem to have become common as navigational devices on ships.

Image courtesy: www.rockingham.k12.va.us/JWES/China/chinacompass.gif

Sextant
Two men independently rediscovered the sextant around 1730: John Hadley (1682-1744), an English mathematician, and Thomas Godfrey (1704-1749), an American inventor. A sextant is a navigation instrument used for measuring angles, primarily altitudes of celestial bodies. Originally, the sextant had an arc of 60°, or 1/6 of a circle, from which the instrument derived its name. Because of the double-reflecting principle used, such an instrument could measure angles as large as 120°. The image shown is of an early sextant by John Bird which was invented in 1759. The frame is mahogany with an ivory scale. It is so large and heavy that it needed a support that fitted into a socket on the observers belt.

Image Courtesy:www.mat.uc.pt/~helios/Mestre/Novemb00/H61_f11.JPG