Great Trigonometrical Survey

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Index to the Great Trigonometrical Survey

The Great Trigonometrical Survey of India was a project that aimed to carry out a

James Walker
, who oversaw its completion in 1871.

Among the many accomplishments of the Survey were the demarcation of the

measurements of a section of an arc of longitude, and for measurements of the geodesic anomaly, which led to the development of the theories of isostasy
.

The native surveyors made use of in the Himalayas, especially in

Krishna Singh Rawat.[2][3][4]

The first triangulations across the Peninsula

History

From its inception in 1600 to its domination of the entire

subcontinent.[5]

Measurement of the Calcutta baseline in 1832 based on a sketch by James Prinsep. This shows surveyors stretching a chain on coffers supported on pickets. The chain is housed under shade to reduce errors due to thermal expansion, and is aligned using a boning telescope.[a]
zenith sector was an upward-facing telescope with accurate angle measurement scales. A star close to the zenith of known declination from the Pole star
was used to determine latitude, as a direct measurement of the pole star could be affected by refraction.

The Great Trigonometrical Survey of India started on 10 April 1802 with the measurement of a baseline near

Mount Delly and Tadiandamol. The distance from coast to coast was 360 miles (580 km) and this survey line was completed in 1806.[7] The East India Company thought that this project would take about five years, but it took nearly 70 years, well past the Indian Rebellion of 1857 and the end of company rule in India. Because of the extent of the land to be surveyed, the surveyors did not triangulate the whole of India but instead created what they called a "gridiron" of triangulation chains running from north to south and east to west.[1] At times the survey party numbered 700 people.[8]

The Trigonometrical Survey was conducted independently of other surveys, notably the topographical and revenue surveys. In 1875, the decision was taken that the Survey budget should be reduced from 240,000 to 200,000 pounds. This resulted in a reorganization under Surveyor-General Colonel J.T. Walker to amalgamate the Great Trigonometrical, Topographical and Revenue Surveys into the Survey of India.[9]

Survey towers used by George Everest to elevate the instruments

Instruments and methods used

Triangulation surveys were based on a few carefully measured baselines and a series of angles. The initial baseline was measured with great care since the accuracy of the subsequent survey was critically dependent upon it. Various corrections were applied, principally temperature. An especially accurate

zenith sector made by Jesse Ramsden
, and 100-foot (30 m) chains. Later surveys used more compact theodolites.

One of the survey towers near Kolkata in 2012

Accurate instruments could not always be purchased through the standard system of government contract, and Everest personally supervised the construction of instruments. He had a maker, Henry Barrow, set up an instrument company in Calcutta. Barrow was succeeded by Syed Mohsin from Arcot, Tamil Nadu, and after his death, the instruments were supplied by Cooke from York.[11][12]

Correcting deviations

To achieve the highest accuracy, a number of corrections were applied to all distances calculated from simple trigonometry:

Superintendents

See also

Notes

  1. ^ A boning telescope was a small, low-magnification telescope used to align the survey markers.[6]

References

  1. ^ a b c d e Gill, B. (2001); "THE BIG MAN. Surveying Sir George Everest", in: Professional Surveyor Magazine, Vol. 21 Nr 2. Retrieved online Archived 10 February 2017 at the Wayback Machine 8 March 2016.
  2. Oxford University
    Press.
  3. ^ Derek J. Waller, 2004, "The Pundits: British Exploration of Tibet and Central Asia," University Press of Kentucky.
  4. ^ Account of the Pundit's Journey in Great Tibet - Capt. H. Trotter, The Journal of the Royal Geographical Society (1877).
  5. ^ Lambton, William (1811). "An account of the Trigonometrical Operations in crossing the peninsula of India, and connecting Fort St. George with Mangalore". Asiatic Researches; or Transactions of the Society Instituted in Bengal for Inquiring into the History and Antiquities: 290–384.
  6. ^ "bone, v.3". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  7. ^ Markham, Clements (1878). A Memoir on the Indian Surveys (2 ed.). London. W H Allen And Co. p. 67. Retrieved 1 March 2009.
  8. ^ Bluesci: Cambridge university science magazine, 29 January 2011,"History: The Great Trigonometrical Survey" "BlueSci » History: The Great Trigonometrical Survey". Archived from the original on 27 July 2014. Retrieved 5 May 2013.{{cite web}}: CS1 maint: bot: original URL status unknown (link), Cambridge.
  9. ^ Black, Charles E.D. (1891). A memoir of the Indian Surveys, 1875–1890. London: Secretary of State for India in Council. pp. 39–40.
  10. ^ R., Ramachandran (2 June 2021) [Originally appeared in print version on April 27, 2002]. "Survey Saga". frontline.thehindu.com. Retrieved 26 December 2022.
  11. ^ Strahan, C. (1903). "The Survey of India". Professional Papers of the Corps of Royal Engineers. 28: 141–171.
  12. ^ Insley, Jane (1995). "Making mountains out of molehills? George Everest and Henry Barry, 1830–39" (PDF). Indian Journal of History of Science. 30 (1): 47–55. Archived from the original (PDF) on 25 January 2014.
  13. JSTOR 108510
    .

Further reading

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