THE PLAN
Brigadier Major William Lambton, an officer in His Majesty’s 33rd Regiment and George Everest. Two landmarks in the arena of surveying and geographic excellence. They were the first to signal the commencement of the Great Trigonometrically Survey in the form of an audacious proposal. The idea was to span the subcontinent ascending the 78th meridian, starting east of Cape Comorin, reaching the foothills of Himalayas. The plans included exploring the territories of Tipu Sultan in Mysore, the Nizam of Hyderabad, the Maratha confederacy of the Peshwa, Holkar, Scindia, Bhonsle, and Gaekwad stretching from the Deccan to Delhi. In its agenda it wasn’t much different from a war or a military campaign, but in its core it was an assignment that needed scientific devotion and military discipline of a massive scale.
Strange’s Zenith Sector No. 1. Manufactured in 1866. Smaller but similar to the Zenith Sector used by Everest and Waugh
Significance of the Arc
The propagation of geographic knowledge was limited before the invention of printing techniques until the 15th century, due to the labour and skills involved in duplicating graphic data. During the middle of 18th century, latitude could be easily measured by observing the meridian altitude of the suns or stars. However, for longitude determination, one had to wait for a favorable phenomenon such as an eclipse of the sun or the moon with similar observations being made at several places.
The intentions were ambitious, military and commercial. The outcome was an unimaginable feat of those times |
In 1787, latitude and longitude measurements were made at several places covering India. The results of the instruments of sextants, chronometers and telescopes used were however perceived to be inaccurate, because of the use of faulty mathematical tables.
The British Empire understood the significance of maps correctly by late eighteenth century. The effectiveness of accurate maps in military campaigns was unquestionable. Many of the wars deemed to be failures by the British were due to lack of proper knowledge of the topography. Geographical knowledge of the Indian princely states was something properly guarded and safe from any potential attacker. Most of the maps produced in the eighteenth century were more from enthusiasm than from accuracy. Large areas were left blank or detailed inaccurately. Hence, the project of measuring an arc of the meridian through a comprehensive mesh of trigonometric surveys covering the whole of the Indian Peninsula was formulated and accepted.
The actual work started on 10th of April 1802 by the measurement of a baseline in Madras. The region was politically friendly and supportive in its endeavour. Fort St George in Madras was a British base since 1640. The countryside surrounds were ideal for the exercise, with drools offering convenience essential for triangulation. The survey began with the measurement of the length of a degree, between two latitudes and two longitudes. Triangle by triangle, a mathematical mesh was conceived and surveyed that covered almost the entire subcontinent.
The box alongside traces the basic steps of the Great Arc process as it happened.The measurement of the Great Arc from Cape Comorin to the Himalayas was completed by 1843. The gridiron system consisted of meridional chains of triangles of triangle tied together at both ends by longitudinal chains. Waugh took over from Everest in 1843 and the triangulation series was extended along the Ganga valley up to Calcutta and then up to Assam. The total triangulation system was adjusted to form a consistent nation-wide standard in 1880. the adjust has remained as a basis of Indian triangulation except for a constant change of - (2’27"18) based on a revision of the longitude of Madras in 1905.
