India's Great Arc: The Survey That Mapped the Himalayas
Science, Empire, and the Quest for Everest's Height

About this book:

They called it the Great Arc—a single, razor-straight line of triangles marching two thousand miles up the spine of India, from the tropical coast of Cape Comorin to the frozen ramparts of the Himalayas. It was the longest measurement of the Earth's surface ever attempted, a project so audacious it consumed fifty years, countless lives, and half-ton theodolites hauled through jungles where tigers stalked the survey camps and malaria felled officers by the dozen. *India's Great Arc* tells the staggering true story of how a ragtag band of British soldiers and brilliant Indian "computors"—led by the irascible genius William Lambton, the tyrannical perfectionist George Everest, and the mathematical prodigy Radhanath Sickdhar—conquered the subcontinent not with bayonets, but with geometry.

This is science writing at its most visceral: the crack of a baseline chain snapping in 120-degree heat; the sickening lurch when a priceless glass prism shatters on a mountain pass; the quiet triumph in a Calcutta computing room when Sickdhar's calculations revealed Peak XV stood exactly 29,002 feet—thirty-three feet shy of modern GPS readings, measured from over a hundred miles away with nothing but light, angles, and intellect. Keay transforms geodesy into high drama, revealing how the quest to map an empire became the quest to measure the planet, settling the great scientific debate of the age: the true shape of the Earth.

Meticulously researched and narrated with novelistic momentum, *India's Great Arc* restores the forgotten heroes—especially the Indian mathematicians whose brilliance made the impossible possible—to the center of one of history's greatest scientific adventures. It is a tale of obsession and empire, of instruments so precise they had to be invented for the job, and of a mountain that got its name from the very man who never saw it. For readers of *Longitude*, *The Mapmakers*, and *Into Thin Air*, this is the definitive account of how humanity finally learned the dimensions of its own world.