Stations of the Arc

Print edition : July 04, 2003

In Chennai, a search for the surviving benchmarks and points of reference relating to the Great Trigonometrical Survey, throws up some interesting findings.

in Chennai

The arrow-like figure found on the structure on the terrace of the St.Thomas Mount Church would perhaps indicate the place from where the plumb line was dropped for the Great Trigonometrical Survey.-M. MOORTHY

IT was a moment to cherish, as a team from the Hyderabad unit of the Survey of India located a few months ago the spot atop St. Thomas Mount, Chennai, from where Col. William Lambton began the Great Arc Expedition. The spot marked the first station of the Great Trigonometrical Survey (GTS), the bedrock of topographical surveys even today, 201 years after Lambton laid out his first baseline from St. Thomas Mount to another nearby hillock known as Little Mount.

Locating the spot was no easy job, and the personnel were overjoyed when they finally succeeded in doing so. A bronze bust of Lambton will be installed near the spot, to pay tribute to him and to commemorate the event.

Omkumar, chief coordinator for Tamil Nadu of The Great Arc Bicentennial celebration, said: "The epoch-making exercise began from here. The first line was laid from St. Thomas Mount. It was an inch-perfect survey". By coincidence, his own office is located a few hundred metres from the foot of St. Thomas Mount. The Indian Administrative Service officer, who heads the Tamil Nadu Technology Mission, expressed his appreciation for the authorities of the church situated atop St. Thomas Mount, who facilitated the work of the team.

Short volumes (sheets) titled "Triangulations in India and Adjacent Countries (G.T. Data Only)" printed by the office of the Survey of India in 1915 give precise locations of scores of GTS stations that dot Tamil Nadu. A typical GTS station consists of a square or rectangular-shaped platform with a pillar on top of it. The crest of the pillar will have a circle with a dot inside, which marks the longitude and latitude of the spot. The foundation stone of the platform, below ground, too will have the circle and the dot. Even if the top of the pillar is destroyed, it will not be difficult to locate the stone below ground using the triangulation method.

The 1915 Survey of India sheet describes the GTS station on the Mount thus: "The station is 50 yards west of the signal flag staff and 19 yards north-west of the north-west corner of the chapel and is identical with the secondary station fixed in season 1864-65, the lower mark of which was fixed and adopted. Col. Lambton's station of 1802 was at the south-west angle of the hill near the chapel... When visited in 1880, the platform of the station of 1864-65 was found to have been removed but the lower mark was intact, a large slab of stone 3.5 feet in diameter was now laid down flush with the ground level. On the upper surface of this stone in addition to the usual circle and dot... indicating the point of observation, a broad arrow and letters G.T.S. 1864 are also engraved. When again visited by the levelling party in 1885-86, the station was found to be in good order."

It has also been recorded that there was a GTS station at Parry's Corner in the heart of Chennai that consisted of a "brass plug of ten cm diameter fixed on the terrace of the s.w. wing of the Parry Building (Dare House)." A search by this correspondent to locate the station revealed a "sight" on the terrace of Dare House, but it turned out to be an anti-aircraft gun sight - a throwback to the War years. It comprised a circular lid made of copper that had readings indicating the latitude and the longitude, and the following description: "This spot is 113.8 feet above sea level. As fixed by the CRE [Chief Royal Engineer] in 1943 for a proposed ackack gun sight."

Opinion is divided on whether a GTS station could have existed on the terrace of Dare House that was built between 1939 and 1941, or whether it was situated on the Parry Building that pre-dated it. The Parry Building was originally the home of one of the relatives of the Nawab of Arcot and Parry & Company bought it in 1803. The GTS station could have been located on the terrace of this building.

A GTS station at Red Hills, about 30 km from Chennai, has "entirely disappeared". At Manpottal in Radhapuram taluk of "Tinneveli" (Tirunelveli) district in southern Tamil Nadu, the station looked like this: "... a platform of stones and earth, 16 feet square and 8 feet high at the outer sides, enclosing a solid, circular and isolated pillar of masonry 3.5 feet in diameter which contains two marks... " At Injambakkam, a suburb of Chennai, the station is situated on a hillock of drift, and between the Buckingham Canal and the seashore. Records reveal that GTS stations were variously located on buildings, including temple gopurams, hillocks, knolls or on level ground.

A further search to locate a GTS station in Chennai city led this correspondent to the Regional Meteorological Centre at Nungambakkam, which has a 211-year history. Within the complex stands a 15-foot tall granite pillar weighing some 15 tonnes that has Lambton's name inscribed on it. The pillar, which is not a GTS station pillar, was part of the Madras Observatory established in 1792 by Sir Charles Oakeley, Governor of the Madras Presidency, with the aid of Michael Topping, a sailor and an astronomer. The majestic pillar is among five monuments that stand within the complex today. On top of this pillar was an astronomical instrument. An inscription on it reads: "The geodetic position... of Col. William Lambton... of Survey of India fixed by him in 1802 was at a point... feet to the south and one foot to the west of the centre of this pillar. The centre of the meridian... of the Madras Observatory was at a point 18 feet to the east of the centre of this pillar." The pillar carries Topping's name also. The year A.D. MDCCXCII is inscribed. There are inscriptions in Tamil, Telugu and Urdu.

A GTS benchmark exists a few metres from this historic pillar. The inscription on it reads: "G.T.S. 1906. The height of the top of this pillar is 21.785 feet above mean level of the sea."

A VETERAN of the Survey of India who is associated with the bicentennial celebrations in Chennai now is Professor L.R.A. Narayan. From the Army he opted to move to the Survey of India where he was trained in survey mapping, cartography, engineering survey, topography, photogrammetry and so on. He has conducted surveys in many remote areas, including deep in the forests of Bastar, in Assam, and in the North-Eastern Frontier Agency, which today comprises Arunachal Pradesh. Narayan recalled his experiences of climbing hills to check observations, and walking for 25 days at a stretch to reach a point called Anini near Tibet. On this trip, food had to be air-dropped to the team. According to him, during a trip undertaken in Nepal, some 2,000 porters carried the equipment that was needed. Narayan agreed that GTS stations were not easy to access.

Besides the installation of a Lambton bust, the celebrations in Chennai will be marked by other events. According to Brigadier Dr. R. Siva Kumar, Head, Natural Resources Data Management System (NRDMS), and the National Spatial Data Infrastructure functioning under the Department of Science and Technology, a Chair in Geospatial Sciences in honour of Col. Colin Mackenzie will be instituted at Anna University in Chennai. The NRDMS and the Survey of India will provide a corpus fund of Rs.50 lakhs to the university for this purpose. Mackenzie founded the Madras School of Survey that later evolved into the College of Engineering, Guindy which, in turn, became a component entity of Anna University.

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