Great Trigonometrical Survey of India

I

Introduction

Great Trigonometrical Survey of India, the 19th-century project to map the subcontinent of India and the adjoining lands north of the Himalaya, carried out first by the East India Company and later by the British imperial government. The Survey was arguably the most ambitious scientific project of the 19th century, and its employees completed journeys of unparalleled challenge, and displayed extraordinary courage, skill, and resourcefulness.

II

Earlier Surveying

Land surveying had been practised in India long before Europeans began to undertake a systematic survey. It had, however, been applied to the measurement of distances along principal routes and of areas of fairly small plots. The coastline had also been roughly charted from ships. After the Battle of Plassey in 1757, which established the rule of the East India Company in Bengal, the Company became responsible for administering huge tracts of country, the geography of which it knew very little. Robert Clive, then in his second term of office as governor of Bengal, decided to produce a general map of all his territory and in 1767 appointed James Rennell to supervise it. Rennell, an army officer then only 24 years old, developed a system of route surveys following main lines of communication. Distances were measured by a perambulator (a large wheel fitted with a device for counting revolutions) and directions by magnetic compass, while astronomical observations were taken at regular intervals to check these findings. Rennell laboured for ten years before he retired owing to ill health. He proved that the Ganga of Greek and Roman mythology was in fact the Ganges. For his pioneering work, he became known as “the father of Indian geography”.

III

The Surveying Task

The Survey proper began in 1800 with the appointment of William Lambton, an officer of the 33rd Foot Regiment, to commence a trigonometrical survey of the extreme south of the peninsula. His work was funded by the East India Company and approved by the government of Madras (now Chennai), both of which had an interest in demonstrating and consolidating their political control over the subcontinent.

Trigonometrical surveys provide a framework of fixed points, the relative positions of which are established with the utmost accuracy. This framework is supplemented by a topographical survey, which fills in the contours of the land and other features. In India the framework was to consist of meridional (north-south) and longitudinal (east-west) chains of connected triangles observed throughout the subcontinent. A base line would be measured on the ground, and the distance from either end to a third point, perhaps marked by a pole erected by flagmen, could then be calculated by trigonometry. One of the newly calculated sides would then be used as the base line of the next triangle, without further need of direct measurement of the ground. Measurements made in this way were checked at regular intervals by astronomical observations, and allowances also had to be made for differences of altitude, the curvature of the Earth, and the refraction of light by the Earth’s atmosphere.

On the ground, difficulties were many. Flagmen were terrorized by tigers. Jungle hid both surveyors and vantage points. South of Madras, palm trees obscured the line of vision across essentially flat country. In the Himalaya, surveyors had to seek out high peaks that would serve as vantage points. Climbing equipment was minimal and instruments were delicate but often extremely heavy. The surveyors often lived off the land, and ill health, particularly malaria, was a constant threat.

IV

William Lambton and George Everest

Lambton first measured two base lines, both about 11 km (7 mi) long, at Bangalore and Madras, using a 30-m (100-ft) steel chain, supported on tripods housed in cases to reduce heat expansion and with capstans to supply tension. The whole assembly would have had to be dismantled and reassembled about 700 times for this operation alone. Astronomical observations were taken at either end of each base line to confirm their coordinates.

Lambton’s most famous piece of equipment was the Great Theodolite, an enormous instrument of brass, glass, and gunmetal, with a graduated horizontal circle 1 m (3 ft) in diameter and weighing, when packed for moving, half a tonne. Lambton devoted the last 22 years of his life to this work, dying in the field. His successor, George Everest, described him as a “great and extraordinary man” who, when preparing to adjust the theodolite, “seemed like Ulysses shaking off his rags”. In 1808 the theodolite was being hoisted to the top of a building when one of the guy ropes broke and the instrument crashed against a wall, buckling its calibrated scales. Lambton took the battered theodolite, apparently wrecked beyond hope, and retired to his tent for six weeks, admitting only his head artificers, while he repaired it with his own hands.

Lambton carried his triangulation from Madras across the peninsula to the western coast by 1805, discovering it to be 65 km (40 mi) narrower at latitude 13° north than earlier maps showed. In central India he moved along the 78th meridian, south to Cape Comorin (1810) at the southern tip of the country, and then north. Meanwhile, Colin Mackenzie, an officer of engineers, was the first to initiate the system by which a complete topographical survey of one sector was completed before the next was begun. His work, on the scale of 1 inch to 1 mile, and based on triangulation, was linked to Lambton’s work as it progressed. In 1818 the East India Company’s project was officially endorsed by the British government, named the Great Trigonometrical Survey (GTS), and extended in scope to cover the whole of India. It was at this point that George Everest joined the GTS, assisting Lambton as he worked his way through central India.

In the 1820s the plane-table—a circular drawing board with an angle-measuring alidade for plotting map positions directly in the field—came into general use. Plane-tablers, most of whom were poorly educated but skilled and highly trained Indians, contributed to the topographical surveying that was the Survey’s principal activity for many years. Maps produced by the Survey were in great demand for civil administration in the early years of the 19th century, an offshoot of the more stable political conditions that began to prevail. Lithographic printing revolutionized the possibilities of map production and although the first few lithographers posted to Calcutta (now Kolkata) reportedly died of “mental disappointment” and disease their successors flourished.

George Everest, who became superintendent of the Survey on Lambton’s death in 1823, and was appointed surveyor-general of India in 1829, broke with traditional practice by choosing to work not in the rainy season but in the cold and dry season. Malaria was less virulent at this time but the air was less clear. He therefore built or used towers with flares on top, taking his sightings from one observation tower to the next by night. His particular contributions to the Survey were to continue Lambton’s project of surveying northward along longitude 78° east; to remeasure the central Indian base line at Bidar; and to adopt the so-called gridiron system, a series of triangulations along meridians at distances of 1°, joined by cross series at intervals of about 6° of latitude. This system was eventually extended to cover the whole of the Indian peninsula and Burma. By the time he reached Dehra Dun in the foothills of the Himalaya in 1834, Everest had directly measured more than 20° of a great circle, the longest hitherto completed. This enabled geodesists to achieve a new level of accuracy in their calculations of the shape of the Earth, as well as permitting the great peaks of the Himalaya to be accurately measured. The distinguished surveyor Kenneth Mason wrote of Everest: “No man before or since has done so much for the geography of Asia.”

From Dehra Dun, a latitudinal (east-west) series of triangles was begun in 1846 along the Nepalese border. A set of triangulation points was surveyed from which 79 of the giant Himalayan peaks could be measured. Each was identified by a roman numeral. Sir Andrew Waugh, who succeeded Everest as surveyor-general in 1843, announced in 1856 that Peak XV was the highest then known. He computed its mean height at 8,839 m (29,002 ft) and named it Mount Everest in honour of his predecessor. Not until 1858, when Captain Thomas Montgomerie had surveyed the Karakorum Range, was it clear that the peaks K1 and K2, though immensely tall, were not as high as Everest. The Survey’s estimates of the heights of these mountains were astoundingly accurate, even though they were made from distances of up to 260 km (160 mi): in November 1999, the height of Mount Everest was remeasured at 8,850 m (29,035 ft).

An important figure in the surveying of the Karakorum was Colonel Henry Godwin-Austen, who when conducting a topographical survey of the area became the first European to explore the Karakorum glaciers and to glimpse at close quarters the “great peak K2”, which was named after him in 1861. Another major contributor to the work of the GTS in Kashmir was an Indian-born Englishman called William Henry Johnson. A man of prodigious energy, he did superb triangulation work and broke the world altitude record year after year, climbing, in 1862, to the height of 6,800 m (22,300 ft). In the early days of the Kashmir survey, he was Montgomerie’s assistant and in the latter’s absence took temporary charge of the triangulation series. After the series was finished, Johnson continued his explorations, becoming the first European since Benedict de Goes (1604) to reach Kotan (now Hotan) in the Takla Makan.