No one knows when exactly Lambton was born; our best guess is 1753. Young Lambton had a passion for science, especially mathematics and astronomy. Once he damaged one of his eyes trying to observe a solar eclipse with inadequate protection!
When he grew up, Lambton started working as a surveyor for the British army in America. He was taken prisoner in the Battle of Yorktown (1781) but was released after the American War of Independence. In 1796, he was posted to India, where he took part in many campaigns. It was during the Fourth Anglo-Mysore War that his navigational skills came to the fore. The most celebrated case was when General Baird led the troops on a night manoeuvre: without realising it, he began leading them towards enemy lines. Lambton, navigating by the stars, corrected the general, and prevented slaughter by enemy cannon.
After the fall of Mysore, British India had become a large colony. Lambton proposed a survey to map this territory accurately. There was administrative, security and commercial justification for Lambton’s idea, because maps of those days were very approximate. There were some reservations in the beginning – some of the higher authorities were not convinced about the project’s significance. Ultimately, Maj. Gen Arthur Wellesley (later the Duke of Wellington) and some other influential leaders backed Lambton, and that was how Lambton began the Great Trigonometrical Survey of India in 1802.
By this time, trigonometry (Greek for ‘triangle measurement’) was a mature science. Lambton used a trigonometric method called triangulation. Its principle was: if you know the distance between two points in a line (the baseline), you can calculate the distance to a third point without actually measuring it; all you need to know is the angles between the two baseline points and the third point. These three points would form a triangle and a trigonometric formula would do the trick! After that, you kept adding adjacent triangles till you measured the whole land.