Great Trigonometric Survey

The Great Trigonometric Survey was a project of the Survey of India throughout most of the 19th century. It was piloted in its initial stages by William Lambton, and later by George Everest. Among the many accomplishments of the Survey were the demarcation of the British territories in India and the measurement of the height of the Himalayan giants: Everest, K2, and Kanchenjunga. The Survey had an enormous scientific impact as well, being responsible for one of the first accurate measurements of a section of an arc of longitude, and for measurements of the geodesic anomaly.

History

The Great Trigonometrical Survey of India started on 10 April 1802 with the measurement of a baseline near Madras. Major Lambton selected the flat plains with St. Thomas Mount at the north end and Perumbauk hill at the southern end. The baseline was 7.5 miles (12.1 km) long. Lieutenant Kater was despatched to find high vantage points on the hills of the west so that the coastal points of Tellicherry and Cannanore could be connected. The high hills chosen were Mount Delly and Tadiandamol. The distance from coast to coast was 360 miles (580 km) and this survey line was completed in 1806. The East India Company thought that this project would take about 5 years but eventually it took more than 60 years, draining the profits of the Company, so much so it was brought under the Crown after 1857.^{[citation needed]}

Baseline measurement

The initial baseline was measured with great accuracy, since the accuracy of the subsequent survey was critically dependant on it. Various corrections were applied, principally temperature. An especially accurate folding chain was used, laid on horizontal tables, all shaded from the sun and with a constant tension.

Corrections

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

• Curvature of the earth
• The non spherical nature of the curvature of the earth
• Gravitational influence of mountains on pendulums
• Refraction
• Height above sea level

Surveyors became landowners

Many surveyors became very rich. Prominent among them was Andrew Chamrette, his son Peter Chamrette, and his grandson Charles Chamrette, who worked for the GTS of India from 1802 to 1876. This family acquired huge tracts of land in village Kapsi district Yavatmal, Maharashtra (formerly CP Berar) amounting to more than 1,800 acres (7.3 km²) and George Everest bought 600 acres (2.4 km²) of land near Dehra Doon.^{[citation needed]}

See also

• Principal Triangulation of Great Britain

Further reading

• Matthew Edney. 1997. Mapping an Empire. Chicago: University of Chicago Press. ISBN 0-22-618488-9.
• John Keay. 2000. The Great Arc. London: Harper Collins. ISBN 0-00-257062-9.

External links

• Royal Geographic Society - Map of the Great Trigonometrical Survey of Indiaca:Gran Projecte de Topografia Trigonomètrica