Author: John Keay
Publishers: Harper Collins
‘The Great Arc’ is the story of mapping India and discovering the highest mountains on earth.
It all began in the first decade of 19th century when the British were slowly establishing their empire, starting with Madras and surrounding territories in South India. An expanding kingdom needed mapping to define and survey its territories. An effort first started by defining the earth surface by a long survey line stretching from Madras to Bangalore. The subsequent surveys got larger and larger, and an ambitious plan was made to measure the terrain along a long line stretching from Cape Comorin (Kanyakumari) to as far north as Agra.
Keay’s story of mapping India comes with some first hand research and some documentary evidences of the survey that have remained. He traces the grave of William Lambton, the great man who initiated the survey in Madras, to a small town in Central India called Hinganghat. He visits George Everest’s office and base station at Mussourie, and goes to many places where the survey team had passed as they made measurements.
Emphasized through the book prominently are the challenges that the survey teams had to endure. Tough and challenging terrains called for some ingenious solutions to carry on the survey. Suspicious natives who did not understand the reasoning behind the survey in those times often did not allow the survey teams in their territory. There was malaria and several other types of fevers to deal with in the monsoons.
The struggle of surveyors to ensure precision in data has been brought out impressively in the book. Just measuring a baseline that marked the beginning of the survey to precise length alone was a job of several months. The process involved considering all possible influential factors, like refraction of light rays from the atmosphere, plumb line deflections from aberrations of earth surface and adjustments for curvature of the earth.
The line from Kanyakumari to Agra eventually took four decades to complete, and was called The Great Arc. The implications of survey data were many – it helped measure earth’s curvature, and aided in making precise measurements of Himalayan peaks that eventually lead to discovery of the world’s highest mountain.
The story of the survey, besides taking the reader through each stage of it, is also a description of lives and temperaments of the great surveyors who toiled for it. While the gentle William Lambton was the initiator of the process, it was taken over by cranky George Everest (after whom Mt.Everest is named) who successfully completed it. Going through the initial parts of the book, which contains technical details of the survey, requires the reader to be equipped with basic knowledge of geometry, without which the book is hard to read and understand. But that hurdle surpassed, it is an excellent read on how India’s geography was understood and mapped.