From dense forests to tough hilly terrain, battling disease, tigers and local resistance, the Great Trigonometric Survey that measured the ends of the country started in Chennai on April 10, 1802
In the plains of the delta region of what was then Tanjore district, two centuries ago, when the biggest exercise of manual land survey was being undertaken, the three-foot tall, half-tonne behemoth of an instrument – ‘the great theodolite’, suffered an injury. The instrument, used to measure angles, took a great fall as one of the ropes meant to hoist it snapped, falling down the pagoda and coming to pieces. But the shattering of the instrument didn’t deter William Lambton, the man instrumental in mapping the vast expanse of the country.
The accident to the great theodolite is just a small hiccup in the Great Trigonometric Survey or The Great Arc, which saw its 213rd anniversary on 10th April 2015. Starting with a baseline of 7.5 miles at Saint Thomas Mount, the survey then moved to Cape Comorin (Kanyakumari) and then extended all the way to the heights of what is now Mount Everest, later travelling north to Kashmir.
Employing the method of triangulation, Lambton dissected the entire country with triangles, using standard 100-foot chains, a motley crew of natives, load-carrying animals and a massive reserve of will.
Triangulation essentially involves starting with the measurement between two fixed points, which then becomes the baseline. Once this is done, the angles and then subsequently the distance to a third reference point can be calculated using a theodolite. And Lambton used this method coming up with what is still considered one of the most accurate surveys, and one of the six greatest events of the era.
Survey of India, Government of India – Report of the Survey of India for 1921–22
“When you conquer a country, you want to know what there is in it, you want to know the shape of the land,” says S Muthiah, Madras historian. In 1799, Mysore Maharaja Tippu Sultan was defeated by Arthur Wellesley-led East India Company forces, following which a series of surveys were undertaken, including the topographic survey led by Colin Mackenzie who eventually became Surveyor General in 1815 and the Trigonometric Survey of the Indian Peninsula.
During this period, Madras was the most important city in India, and major landmark events had their beginnings here, says Muthiah. The GTS too had its roots in the port city. Bridges were built, railways chugged in. And the shape of the country too as we know it today began emerging in 1802 under the helmsmanship of Lambton.
Herculean task
The physical difficulties of the survey that were braved by the troops boggles the mind of historians and surveyors today, where sophisticated technology, air conditioned vehicles and GPS have made processes simpler. The reference points used even now are still the two-century marks.
When the government of Madras sanctioned Lambton’s survey, he put together a company that spent weeks in the forests, months to clear vegetation in the hills to set up stations , and brave threats of germs like malaria. It was in 1818 that Colonel Everest joined the expedition as second in command.
There are records where Lambton has observed that “the entire native establishment was struck down with malignant fever. Many perished miserably at the roadside.” The story of their journey has been recalled both in the ‘Account of the Operations of the Great Trigonometrical Survey of India’ by the Survey of India, and in newspaper accounts. An article from The Argus newspaper in Melbourne in September 1873 cites journal records of Everest, who wrote the following when the survey extended to the Godavari-Krishna basin.
“The climate,” wrote Everest, “Was very deadly. It is easy to conceive what a waste of life and health was caused by this exposure to the pitiless pelting of the tropical rains, in forest tracts teeming with miasma, …. tents decomposing into their original elements..”
In addition to succumbing to such fevers and the ferocity of wild animals, in several places, tribals were up in arms against the company. In Travancore too, Lambton was forced to put down his instruments and pick up a sword to do battle and later set up fortifications, according to the Argus. They also had difficulties several times getting permission from the local kings, and many a time Lambton was asked to do only one part of the survey and skip the verification which was done with 65-foot chains.
By some accounts, over the course of the entire survey lasting about 70-100 years, the number who died could outnumber the 18th century wars’ tolls in India.
Finding an elevated point to carry out measurements was another difficulty. Hillocks were a good option to mount the instruments, and in many arts of south India, temple gopurams were used. In parts of North India, 60-foot towers were constructed in order to do the survey. Platforms would have had to be built for the theodolite, and scaffolding constructed, says D H Rao, veteran civil engineer and Madras history enthusiast.
Whenever the group entered a district where triangulation had not been done, the company would be asked to make a preliminary survey and also furnish sketches of any forts in the region, for military purposes.
At one point, he was even asked to stop, as fear has arisen among the British officers about multiplying copies of the maps, and he was required to return all the maps. But this too, was soon overruled and he was back on his feet like before.
‘He was still in the prime of life and and the full vigour of an unusually robust and energetic manhood, he was hardly known to have had a day’s illness,” say records, and so he remained, dedicated to the survey until he met his end at Maharashtra, where his body still lies.
How It was Done
A research paper states that the measuring chain consisted of 40 interconnected, each 2.5-foot iron rods, and the chain was kept in five specially constructed 20-foot long wooden crates to protect them from the sunlight. The boxes were mounted on adjustable stands, so that the chain could be aligned to an exact straight line. The accuracy was to the dot- temperature would be measured in the boxes to take into account metal expansion or contraction – The quantity of this correction was .00725 inch for every degree of Fahrenheit. .
A typical company consisted of four elephants for the ‘tiger-wary’ principals, 30 horses for military officers and 42 camels for supplies and equipment. However, “Camels were not present in the South. They used pack bulls,” points out Muthiah. The 700 or so labourers traveled on foot.
From 1802 to 1815, Lambton had covered the entire land mass covering Cape Comorin in the South to the Maratta empire’s southern-most territories; and from Goa in the West to Masulipatnam (Machilipatnam in Andhra). Following this, it was decided that the survey would be further expanded.
“Today, we do what is called rapid survey, and to do a 25 feet by 25 feet, it would take four people one month. You do the math,” says a Survey of India official.
But the Great Trigonometric Survey would still be more than what we would do today, he admits. Though there is GPS, he says, even that comes with varying degrees of accuracy, and now, officials do the ‘rapid’ survey by using vehicles and driving around, not by climbing unexplored hilltops and lugging around apparatus. The records say that Lambton was even prepared to recognise influence of not only irregularities in earths surface but also varying densities beneath the surface, which was proved only half a century later.
Even 213 years later, the relevance of the survey is still intact – the great arc that cut across the lands still makes its mark – An indelible mark that reticulated the area between Kanyakumari and the Himalayas and mapped the area of 1.47 lakh square kilometres.
Note: I worked on this piece with another talented journalist who is now my wife 🙂
Leave a Reply