Story of one man and his theodolite

Most people probably imagine that Mount Everest, the world's highest mountain, was named for its apparent meaning, like the Dead Sea or the South Pole. In fact, it was named after a choleric, overdriven British surveyor who never saw the peak and who took serious umbrage when people mispronounced his name, which was George EVErest.

This irony is of exactly the kind that appeals to John Keay, a historian with a natural instinct for the ambivalence in the relationship between Britain and India, which over the past quarter of a century he has described in various books including When Men and Mountains Meet , a history of the exploration of the western Himalayas. The Great Arc displays all of Keay's many qualities as a researcher, traveller and writer - particularly his pleasure in depicting eccentricity - in telling the story of how India was mapped by the Great Trigonometrical Survey during the first half of the 19th century. Perhaps no other writer could have come up with this perfectly judged image of George Everest during a night shift on the plains of northern India: "Supposing the theodolite to be a camera, the scene must have resembled that of a night shoot on a movie set. In the ingenious use of bamboo scaffolding the Bombay film industry probably surpasses the Survey; but in the hush of expectation as Everest climbed to his platform and 'stood to the instrument', in the cry of 'Lights!' and in the endless retakes, any movie-maker would have felt at home... [Everest's] role was that of orchestrating a vast production in which his various 'crews' were expected to heed his every command without necessarily comprehending his vision... Creative genius was at work; an enormous expenditure had to be justified, a perfectionist's reputation upheld, and a monumental ego sustained."

There is a considerable amount of science in the book - rather more than in the comparable (if less readable) Longitude by Dava Sobel - which Keay handles deftly and clearly, though he could have done with a few more diagrams. The basic idea, as in any surveying, required the laying of a number of accurately measured baselines as the survey proceeded, from which successive triangulations enabled India to be covered with points of known position and elevation. The goal was to map a great meridional arc from the deep south of India to the foothills of the Himalayas. But in order to do this, the surveyors had to surmount a wide range of tricky problems (apart from appalling, frequently fatal illness), such as atmospheric refraction, the curvature of the earth and the deflection of plumblines by crustal rock of differing density. Throughout there was also the question of how to achieve sightlines, particularly in the plains, when these were obstructed by trees, temples and villages, not to speak of the haze caused by dust and thousands of cow-dung cooking fires. In due course, the survey took to working with highly visible flares at night; and it was sometimes necessary to build special towers for observation, a handful of which still remain as mouldering symbols of a long-forgotten age.

Inevitably, there was conflict between the East India Company and the British government that succeeded it, and the "men on the ground". Officials in London and Calcutta saw the survey as principally utilitarian; it was a way of imposing a "steel frame" (the phrase later used to describe the Indian Civil Service) on their newly conquered dominions, so that they could be taxed and administered. But for Everest, and especially for William Lambton, the founder of the survey in 1802, the primary motive was a loftier one: to aid the cause of science, not empire.

Keay draws an affectionate portrait of the mild-mannered "elusive" Lambton, who seems to have been determined to cover his tracks. He even poignantly traces Lambton's gravestone to a crumbling corner of an insalubrious town in the very centre of India, and discovers from the broken inscription that Lambton was probably born a decade later than given in the official history of the survey. Where Lambton, with his passion for geodesy, his loyalty to his Indian-born assistants, his various offspring born of local liaisons and his lack of interest in fame, is reminiscent of the many British officers who "went native" in the early years of British rule, Everest is almost a prototypical Victorian sahib, given to violent, if occasionally entertaining outbursts of rudeness, especially to his "mestizo" subordinates. Many of his fellow countrymen were hostile to him and resisted his name being lent to the highest mountain. Everest himself, by now Sir George and living in comfortable retirement in England, wisely kept mum during the controversy. Given such an honour, even he was not going to complain about a mispronounced syllable.

Andrew Robinson is literary editor, The THES , and the author (with Simon Berthon) of The Shape of the World .