# The Great Trigonometrical Survey begins
**महान त्रिकोणमितीय सर्वेक्षण का आरंभ**

- Canonical page: https://indianepics.online/event/great-arc-1802/
- Chapter: [Company rule](https://indianepics.online/chapter/company.md)
- Track: evidence (archaeology and documents)
- When: 1802 CE
- Where: St Thomas Mount, Chennai (13.005, 80.194)
- Tags: science, colonial

## Summary

On 10 April 1802 William Lambton lays a 12 km baseline near Madras, the start of the survey that mapped India and measured Everest.

10 अप्रैल 1802 को विलियम लैम्बटन ने मद्रास के पास 12 किमी लंबी आधार-रेखा नापी; इसी सर्वेक्षण ने भारत का मानचित्र बनाया और एवरेस्ट को नापा।

## Account

Lambton laid his first baseline across the flat ground between St Thomas Mount and Perumbakkam, about 7.5 miles long, measured with a steel chain. From it a chain of triangles was carried across the peninsula and then north along the meridian near 78 degrees east. George Everest, who succeeded him in 1823, extended this Great Arc from Cape Comorin to the foothills of the Himalaya.

The Survey of India's maps were built on these triangles for more than a century. The survey fixed positions and heights to a standard no earlier map approached, and turned territory the Company claimed into territory it could measure, tax and defend.

In 1852 computations in the survey's Calcutta office identified Peak XV, on the Nepal-Tibet border, as the highest mountain then known. The work is traditionally credited to the chief computer Radhanath Sikdar, though the well-known story of his announcement is anecdotal. Andrew Waugh published the height, 29,002 feet, in 1856, and the peak was named after Everest, over his own objection, in 1865.

## Sources

- Walker, Account of the Operations of the Great Trigonometrical Survey of India, vol. I (1870) — https://archive.org/details/in.ernet.dli.2015.176666
- Phillimore, Historical Records of the Survey of India, vol. I, 1800 to 1815 — https://archive.org/details/dli.ernet.11481
- Keay, The Great Arc (2000)

## Image

William Lambton. Unknown authorUnknown author, Public domain, via Wikimedia Commons: https://commons.wikimedia.org/wiki/File%3AWilliam_Lambton.jpg

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