As the Department of Science and Technology celebrates the bicentenary of The Great Arc expedition, the cross-country survey and mapping exercise, India's expertise in the field, and the globally competitive position of the Survey of India, comes into focus.
ONE of the unresolved scientific questions of the late-18th century related to the exact shape of the earth. It was generally known that the earth was not a sphere but an `oblate spheroid', that is, more curved at the Equator and flatter at the poles. But the question, `how much more', remained.
The length of the arc of a degree of latitude is a measure of the curvature of the earth at that point. For a spheroid, if one determined the length of the arc along a chosen longitude or meridian at one degree latitude separation, the length of one degree arc should be less near the equatorial latitudes than at the poles. That this was so had been established in the 1730s by French survey expeditions to Ecuador near the Equator and Lapland in the Arctic, which found that around the middle of the earth the arc was shorter by about a kilometre.
The Great Arc experiment was primarily conceived by the British Surveyor Col. William Lambton to do a similar measurement in the tropical latitudes by means of the technique of `triangulations'. The idea was that by measuring the distance over a longer arc in the Indian subcontinent one would be able to do better and obtain a more precise measure of the earth's `oblateness'.
Lambton was an engineer, a mathematician and an astronomer but had a sustained interest in geodesy. He had assisted in the surveying of the New Brunswick area, which was carried out to delineate the boundary between British Canada and the United States. He had joined the British Army. He was posted to India in 1796 and took part in the Fourth Anglo-Mysore War, known as the Tipu War.
The project was proposed in 1799 and approved in 1800. In his proposal for a "Mathematical and Geographical Survey", Lambton noted: "In a former communication I took the liberty of stating... my idea of a survey to be extended from the Coromandal to the Malabar coast, with a view to determine the exact position of all the great objects that appeared best calculated to become permanent geographical marks... facilitating a general survey of the peninsula and particularly the territories conquered... during the late glorious campaign... The surveyors of particular districts will be spared much labour when they know the position of some leading points to which they can refer because, when these points are laid down in the exact situations in which they are upon the globe, all the other object... will also have their situations true in Latitude and Longitude... I have now adduced... the principles of my intended survey... which... involve many more objects than what immediately appertain to Geography... Whenever a cooperation with Captain Mackenzie (whom he was assisting in the Mysore Survey) can be dispensed with, I shall direct my views to the General object of determining the geographical features of the Peninsula."
It took two years for a suitable theodolite to come from Britain. The theodolite is a key instrument for a surveyor, is essentially a telescope mounted in an elaborate structure so that it pivots both vertically, about an upright ring or `circle', and horizontally, about a larger horizontal circle. This enables the angle of elevation as well as angles in a plane to be read off the instrument's calibrated circles. Plummets, spirit levels and adjustment screws allow alignment and levelling, and micrometers and microscopes enable reading the calibrations. On April 10, 1802, Col. Lambton, braving the heat of the Indian summer, began this ambitious scientific odyssey at St. Thomas Mount in Madras (now Chennai). The first baseline for the triangulation sequence, and thus for the "measurement of the length of a degree of latitude" along a longitude in the middle of peninsular India, was carefully laid, stretching across a distance of 12 km on a flat plain between St. Thomas Mount and a hillock at the southern end. The measurement of this first sea-level horizontal stretch of 7.5 miles (12 km) took 57 days because Lambton's meticulousness required over 400 measurements to be made with a 100-ft steel chain. Lambton had carried out a trial survey of a baseline near Bangalore as part of Mackenzie's topographic survey of Mysore.
Lambton's original plan of a short arc, grew in size and scale to become "one of the most stupendous works in the history of science", one of the greatest human endeavours ever undertaken. His original idea was to measure an arc confined to the southern peninsula - from the southern tip at Cape Comorin (now Kanyakumari) to 18 degrees latitude near Hyderabad along the 78 degrees meridian - that would yield the `length of a degree of latitude'. But soon the potential utility of extending the arc further up north became obvious to him (Frontline, May 10, 2002).
Lambton realised that the Great Arc could serve as the "trunk of a tree" or "spinal column of the skeleton" that would embrace the entire country and could be used as the basis and benchmark for regional surveys - the Madras Survey, the Bengal Survey and the Bombay Survey - which were being carried out as the control and influence of the Raj slowly spread. The Great Arc would form the basis for the mapping of the entire country mirroring the progress of the empire, as it were. It grew into what is known as the Great Indian Arc of the Meridian, a mammoth web of `triangulations' that ran roughly along the 78 degree longitude across the entire length of the subcontinent covering a distance of about 2,400 km in the north-south direction. (Triangulation involves identifying three mutually visible reference points, usually prominent hills or buildings, as the corners of a triangle. By finding the exact distance between two of these points, and then measuring the angles made at each by the respective lines of sight with the third reference point, the distance and position of the third point can be deduced by simple trigonometry. One of the newly determined sides of this triangle would now serve as the base-line for a second triangle that will include a new reference point whose position would, in turn, be established by the same procedure. Another triangle is thus completed which serves the basis for yet another new triangle and so on. Thus, a chain of triangles results.)
After the Madras baseline measurement, Lambton could begin his triangulation only in September. He completed the short meridional arc from Madras to Cuddalore. This short southern series of triangles down the coast took about a year. In October 1804, he headed westward and inland and carried his triangulations towards Bangalore and beyond.
Lambton's first longitudinal (east-west) arc across the peninsula (as against the north-south latitudinal arc) yielded an interesting finding. It seemed that the peninsula had shrunk! Against the value of about 400 miles of the then current maps, which were based on coastal surveys and astronomical references, Lambton's accurate triangulations showed that it was only 360 miles from Madras to Mangalore.
In 1805, Lambton returned to Bangalore to continue his original mission - the north-south measurement of the Great Arc of the Meridian. With Bangalore as its starting point, Lambton's triangles extended north about 100 miles up to where the independent territory of the Nizam of Hyderabad lay, and then south towards Cape Comorin. The next baseline was measured at Coimbatore in 1806. The following fact gives an idea of the accuracy of Lambton's measurements: In its length over six miles, the difference between the triangulated measurement carried from Bangalore along the Great Arc and the actual measurement at Coimbatore was only 7.6 inches.
In 1809, Lambton completed the Coimbatore-Cape Comorin section of the Great Arc - with an equally accurate base-line check at Tirunelveli. By 1815, Lambton had covered the whole peninsula south of the Krishna river, which resulted in the measurement of the longest geodetic arc closest to the Equator, from Cape Comorin to the 18th Parallel. With the more refined measurements on a longer arc, the length of a degree of latitude as calculated from the short arc from Madras in 1802 was soon revised. As the arc got longer, the parameters associated with the curvature of the earth were recalculated. Isaac Newton's value for the flattening of the earth at the poles was 1/230. It was revised down to 1/304 in 1812, and by Lambton himself to 1/310 in 1818. Lt. George Everest, who joined Lambton in 1818, was later to revise the value to 1/300.8.
With the help of Everest, Lambton convinced the Nizam of Hyderabad to permit passage further north. This meant that the Great Arc moved out of the control of the Madras government. Lambton's survey was transferred to the supreme government in Calcutta and the survey was officially christened the Great Trigonometrical Survey (GTS) of India. Lambton now hoped that the survey would continue north, east and west at least until lateral triangulations could link Calcutta and Bombay.
Lambton's plan was to continue on the same 78 degree meridian from Hyderabad to Nagpur. But he died on his way to Nagpur at the age of 70 in 1823 in a place called Hinganghat, before he could fulfil his dream. Of all his contributions, the greatest was the measurement of the meridional arcs. His results were employed well into the 20th century in all investigations of the figure of the earth.
GEORGE EVEREST continued the mission of the Great Arc. However, he wanted to improve upon Lambton's work by basing the surveys on a rigid reference framework - a suitable reference spheroid to fit the shape of the earth's surface in the region of the subcontinent. With Kalianpur in Madhya Pradesh, more or less the centre-point of India, Everest conceived covering the length and breadth of the country by a `grid-iron' of triangular chains, as against a network of triangulations as conceived by Lambton. He redesigned the Great Theodolite and replaced the steel chain with 10-ft compensation bars.
Everest had heard of Col. Colby's work with compensating bars on the Irish Survey, and visited him there in 1829. He acquired a double set for the Great Arc and practised with them at Greenwich near London. In June 1830, Everest returned to India, this time as Surveyor-General, in addition to his post as Superintendent of the GTS. Everest set up a baseline near Dehra Dun using the Colby compensating bars. The 39,183.783 ft baseline was meticulously surveyed. He then linked the Dehra Dun baseline to the Sironj baseline, a distance of over 400 miles, using a triangulation grid iron. By May 1836, half of the gap between Sironj and Dehra Dun had been completed, and the rest was completed the following season. Everest then extended the Great Arc further north up to Banog, in the first Himalayan range, near Mussoorie, covering a length of 2,400 km. He completed this, along with Lambton's associates, in 1841; he took two more years to carry out computations and adjustments.
The work done and the norms laid down by Everest have stood the test of time. The Everest Spheroid, the reference frame for the Indian region, evolved by him in 1830, is still being used in India (with some revisions) as also by Pakistan, Nepal, Myanmar, Sri Lanka, Bhutan and other South Asian countries. His concept of a grid iron network forms the basis of accurate surveys of the entire country and forms a solid foundation for mapping for defence and other developmental needs.
An offshoot of the GTS was the demonstration of the Himalayas being the highest mountain range in the world. It was with the help of the grid iron network that Everest's successor, Surveyor-General Andrew Scott Waugh, observed and discovered the world's highest peak in 1852. Assisted by the survey's `chief computer', Radhanath Sickdhar, its height was determined to be 29,002 ft (8,840 m). After fresh observations and computations, the Survey of India declared its height in 1954 to be 8,848 m.
The triangulation of India as completed by 1870 is shown in this index chart of the Great Trigonometrical Survey.
It is not known whether Sir George Everest ever laid his eyes on the peak that bears his name, but Waugh's admiration of Everest's achievements led to the naming of what was known as "Peak XV" as Mount Everest. Waugh wrote: " ...here is a mountain most probably the highest in the world without any local name that I can discover..."
The Great Arc was the longest measurement of the earth's surface ever to have been attempted. Lambton and Everest made these monumental contributions to the GTS at a time when no communication network existed. The country was marked by jungles and their wild animals, mighty rivers and swamps. The weather was hostile and infectious diseases, particularly malaria, were rampant. Their journey of discovery involved moving across the subcontinent with diverse measuring instruments. The massive theodolite had to be carried by as many as12 men to be placed at innumerable vantage points to make measurements - sometimes atop a temple gopuram, sometimes atop a church, sometimes atop temporary 30-m high structures.
The average length of a side of a triangulation was 31 miles, and the maximum was 62 miles. One cannot imagine how such long-distance measurements were planned, laid down on the ground, the line of sight cleared of trees and sometimes even houses and other structures. If Lambton went on relentlessly despite itinerant fever and ailments such as dysentery, Everest did all this despite his paralysis and poor health.
In its post-Independence phase, the Survey of India (SoI) has consolidated the work of Lambton-Everest and mapped the entire country on 1:50,000 scale and about 40 per cent of it on 1: 25,000 scale. With advances in instrumentation and measurement techniques and the advent of digital technology, the SoI is at present in the process of digitising the existing topographic data on 1:50,000 scale to serve Geographic Information System-based (GIS) developmental projects (see interview with the Surveyor-General of India, featured separately). In order to honour the memory and the contributions of the two great surveyors, the SoI is celebrating the bicentenary celebrations of The Great Arc both within the country and in the United Kingdom.
IN connection with the Great Arc Bicentenary, the Survey of India has organised a number of events.
On April 10, 2003, Dr. Murli Manohar Joshi, Union Minister for Human Resource Development and Science and Technology, inaugurated the celebrations in New Delhi.
A `treasure hunt' for schoolchildren was staged in order to enable them to experience the thrill of walking the unknown and then lead the teams on a journey of discovery for the `treasure' through the bylanes of the national capital.
A national seminar titled `GTS to GPS: Geodesy on the Move' was held in Dehra Dun in February 2003. It deliberated on the scientific progress made since the Great Trigonometrical Survey (GTS) till the present time in the field of geodetic sciences. (GPS stands for global positioning system.)
A float that featured the work of the Survey of India was on display at the Republic Day Parade in New Delhi this year.
Coming events include the release of a pictorial book on the Great Arc by John Keay, a British historian who authored The Great Arc: The Dynamic Tale of How India Was Mapped and Everest Was Named. (A review of the book appeared in the September 27, 2002 issue of Frontline.)
Films on the Survey of India, the GTS and on the Indian explorers are being produced by a Delhi-based agency.
An exhibition showcasing the work of the Survey of India through the last two centuries and its future plans is being put together by the National Institute of Design, Ahmedabad. The exhibition will go around the country seeking to generate among the public, interest in and knowledge of geography. By arrangement with the British government, a module from this is being sent to London to be displayed there.
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