It is scarcely necessary to say [wrote Lambton] what the advantage will be of ascertaining the great geographical features upon correct mathematical principles; for then, after surveys of different districts have been made in the usual mode, they can be combined in one general map.
In other words a trigonometrical survey would provide an extremely accurate framework within which topographical and route surveys, like those of Mackenzie and Buchanan, could be fitted. The principle had already been established in Britain by General Roy’s Ordnance Survey, which no doubt gave Lambton the idea. While the topographical surveyor must carefully sketch
and measure every inch of the ground, the trigonometrical surveyor leaps across the countryside from one eminence to the next. Extreme accuracy was of the essence: the stations he established would become the pole stars of all future topographical surveys. Though comparatively few surveyors would be needed, the instruments required were complex and cumbersome. Factors such as the curvature of
the earth had to be taken into account, and it was one of Lambton’s great ambitions to establish precisely what this amounted to in a latitude such as India’s. The scheme therefore had both practical and scientific implications, both of which recommended themselves to Mackenzie as the Madras Surveyor-General.
But in the enthusiastic support that Lambton received from Wellesley and the Governor-General,
there must also have lurked a political consideration. The trigonometrical survey was of no immediate military or strategic relevance, was not essential for the purposes of revenue assessment and was unlikely to lead to the discovery of useful plants, interesting buildings, etc. Unlike all the other surveyors, Lambton would not be sidetracked onto matters other than his triangles.
But what the
trigonometrical survey did do was embrace the whole of India. In its adoption lay the seed of an idea that would soon translate itself into the reality of an all-Indian empire; and in its completion would lie the important acknowledgement of India’s physical integrity. Just as Ashoka had staked out his empire with pillars and stone-cut inscriptions, so the British would stake out their own claim
with trig stations and the maps that resulted.
Between 1800 and 1802, Lambton carried out what amounted to a practice exercise around Bangalore. Trigonometrical surveys started with measuring, along the ground, a base line using a specially wrought chain, levelled and stretched to give absolute accuracy. The chain, along with all the other instruments used by Lambton, had been bought secondhand
from a Dr Dinwiddie in Calcutta. They would have been in Peking but for a lucky coincidence: the Chinese had not regarded chains, and what looked like other instruments of torture, as suitable presents for His Celestial Majesty. Dinwiddie was therefore escorting them back to England via India, and only too happy to be relieved of his charge.
Outside Bangalore, a suitably level piece of ground
was selected and operations began. The chain, of blistered steel, was 100 feet long. To ensure that it was taut, level and not subject to extremes of temperature, it was housed in five long wooden coffers, each twenty feet long. These in turn were supported on tripods equipped with elevating screws for levelling; the coffers were also equipped with thermometers, as temperature was an important factor
in any expansion of the chain.
The base line in this case was 7.44 miles long, so the chain, coffers and tripods had to be dismantled and re-erected nearly 500 times. This was done by a carefully drilled squad, twenty men to the chain, more to the coffers, acting on the word of command. The whole operation took fifty-seven days. Flooding, possibly contrived by the locals, interfered; but Lambton
was confident that ‘no error exceeding eight or ten inches’ over the whole distance was possible. Then came a series of astronomical observations to establish the latitude at each end of the base line. For this an instrument called a zenith sector was required; the one bought from Dinwiddie was held in two large coffins which it took fourteen men to carry.
Finally, the base line measured and
its position determined, triangulation could begin. A suitable hill was selected, a pole was erected on top of it and, using a theodolite, the angle between the base line and a line to the hill was measured at each end of the base line. Knowing, now, the length of the base and the two angles, the length of the other two sides could be worked out and the position of the hill minutely ascertained. One
of the lines to it then became the base for the next triangle. And so on. The survey could at last stride off across the country. From time to time it was essential to check for accuracy by measuring another base line and by taking further observations. But, theoretically, so long as the original base was precisely measured, and the necessary allowances made for variations of altitude, the curvature
of the earth, and refraction, the deviation should never exceed a few inches.
Although the base lines and triangles measured in 1800–2 were only a practice run, the principles and procedures remained the same throughout what became known as the Great Trigonometrical Survey (GTS). There were difficulties – the lack of suitable hills in the plains, for instance. And there were refinements – flashing
lights instead of poles, for one. But Lambton’s scheme based on ‘correct mathematical principles’ did indeed prove capable of being continued ‘to an almost unlimited extent’.
In 1802, provided with new instruments from England, including the Great Theodolite weighing exactly half a ton, Lambton started his coast-to-coast series. He measured a base line above the beach in Madras and from this
extended triangles up and down the coast to measure a short arc of the meridian which would give him the curvature of the earth in that latitude. Then, in 1803, he headed west, reaching the Malabar coast near Mangalore two years later. His measurements showed the peninsula to be 360 miles wide at this point, forty less than current maps showed.
In 1807, he started south to extend his triangles
to Cape Comorin so as ‘to form a complete skeleton of the peninsula’. He tried going down the coast, but at Nagore, south of Pondicherry, ran into difficulties.
The work was here brought to a standstill owing to the height and the thick growth of the palm trees which everywhere obscured the view. The difficult and dangerous method was adopted of building scaffolds on top of the highest pagodas [temples] and of hoisting the heavy apparatus up by machinery constructed for the purpose, but without success; no stations whatever could be found with the necessary visibility and it was with some difficulty that the pagoda at Nagore was laid down.
He decided to move inland and, using more temples, reached Tanjore. Here this ‘difficult and dangerous method’ resulted in disaster, and the whole
GTS was placed in jeopardy. The great tower of the Tanjore temple, 216 feet high, had proved irresistible; but in winching the half-ton theodolite to its summit, the guy rope used to keep it clear of the structure snapped; the theodolite crashed against the tower. Any damage to the temple Lambton does not record; he was far too concerned about his instrument.
The blow was received on the tangent screw and its clamp. The case, being insufficient to protect it was broken, and the limb, instead of being a beautiful circle, was so distorted as to render it to all appearances worthless.
It looked as if operations would have to be suspended indefinitely. Lambton retired to the nearest ordnance depot and shut himself away in his tent with his beloved theodolite. No one, except a couple of
assistants, was allowed to enter.
He then took the instrument entirely to pieces [writes his successor] and, having cut out of a large flat plank a circle of the exact size that he wanted, he gradually, by means of wedges and screws and pulleys, drew the limb out so as to fit into the circumference; and thus in the course of six weeks he had brought it back nearly to its original form. The radii, which had been bent, were restored to the proper shape and length by beating them with small wooden hammers.
The work could begin again. By 1810 Lambton had finished his triangulation of the southern tip and returned to his original coast-to-coast series to extend it northwards. He was now approaching sixty, and increasingly left the triangulation to his assistants, concentrating his own flagging
energies on new base lines and calculations. But, reliable as his assistants were, there was as yet no one who could be considered as his natural successor. ‘Someone possessing zeal, constitution and attainments’ was desperately needed.
In 1818 the government rose to the occasion by nominating George Everest, a young artillery officer with an outstanding aptitude for mathematics and a good surveying
record. At about the same time, the Survey reached Hyderabad territory and was transferred from the Madras government to the Supreme government in Calcutta. It was officially designated as the Great Trigonometrical Survey, and its extension to the whole of India right up to the Himalayas was sanctioned. The future was assured. But Lambton, now a Colonel, was slowing up. ‘Men cannot last forever’,
observed Everest in 1822, ‘the Colonel’s infirmities have evidently subdued all but his spirit.’
It is now upwards of twenty years since I commenced it [the Survey] on this grand scale [wrote Lambton], In this long period of time I have scarcely experienced a heavy hour; such is the case when the human mind is absorbed in pursuits that call its powers into action. A man so engaged, his time passes on insensibly&. I shall close my career with heartfelt satisfaction and look back with increasing delight on the years I have spent in India.
But there was to be no time for looking back. Aged seventy, he embarked on the 400-mile journey across the Deccan from Hyderabad to a new headquarters at Nagpur. Fifty miles short of his destination he died in his tent. ‘As he ever looked forward
to dying, so he died, at his post’, wrote a later Surveyor-General.
Everest was to prove a worthy successor to Lambton in everything except constitution and temperament. Whilst Lambton was seemingly impervious to India’s climate, Everest succumbed to every fever going and was never free from ‘my old complaint’ – probably amoebic dysentery. His correspondence is filled with detailed bulletins.
In 1824 he was paralysed for a time and had to be lifted in and out of his seat at the zenith sector. In 1835 his hip seized up and he recovered only after ‘the application of some hundreds of leeches – fomentations administered night and day – a due abstraction of blood from cupping – and a course of gruel diet’. Three years later he collapsed again.
I was attacked in November last near Sironj with a severe illness&. Dreadful rheumatic pains in my bones-fever-loss of appetite — indigestion — intestines totally deranged — stomach totally powerless – my strength entirely gone – the whole system apparently destroyed and forever undermined. I recovered gradually & but found to my indescribable dismay that my memory was in a great measure gone – that my mind was affected – that whatever I did or thought of during the day preyed on me at night – and worst of all I found myself oppressed by a dreadful foreboding of ill – a horror of being awake in the dark – an apprehension even whilst I was wide awake, of some spectre or monster of fancy coming to hold converse with me & I thought it would certainly end in madness.
Apart from five years home leave (1825–30), this state of perpetual
convalescence was not allowed to interfere with the progress of the Survey; but it certainly contributed towards making George Everest one of the most cantankerous
sahibs
in history. When he took over the GTS most of Lambton’s assistants promptly resigned. Those who succeeded them were bullied and browbeaten unmercifully. Everest seemed incapable of sustaining any professional relationship other
than as a vendetta. He chastised his native staff, berated local officials, and met every directive from Calcutta with a howl of protest. No man can have been less prone to misgivings about the importance of his work, and woe betide anyone who interfered with its smooth progress. Any dog or cat straying into his camp was promptly shot, and an officer whose horse presumed to neigh outside the Surveyor-General’s
tent was threatened with a court-martial for insubordination.
But, if not exactly loved, Everest commanded great professional respect. No one could question his dedication. During twenty years as Superintendant of the GTS he carried Lambton’s triangulation from Berar through the wilds of central India and across the plains of the Ganges to Dehra Dun in the Himalayas. The line of triangles, stretching
from Cape Comorin to the mountains, was the longest arc of the meridian ever measured, and of immense geodetic importance for calculating the curvature of the earth. This great arc was Everest’s most important achievement, and it has formed the backbone of maps of India ever since. But he did not neglect the rest of the skeleton – from the great arc, another series of triangles stretched
east to Calcutta, and a third was started, east along the base of the Himalayas. These two were connected by further meridional series and a grid was thus thrown over a large part of north India.
All this was possible thanks to more accurate instruments, a much larger staff, increased expenditure and a number of innovations. Everest rejected Lambton’s chain for base line measurements in favour
of the new compensation bars, which eliminated the stretch caused by expansion. The first time these bars were used was for the Calcutta base line measured in 1832. A sketch of the operation by James Prinsep, ever an enthusiast in such matters, shows the bars mounted in coffers and supported on tripods as in Lambton’s day; in the background can be seen one of the towers erected at each end of the
line. Towers became an essential part of the survey in the plains of the north. With a heavy smoke and dust haze invariably covering the ground, and with no handy
gopurams
or hills, scaffolding towers of bamboo, seventy feet high, were erected, as well as some masonry towers for the more important trig stations. Even then, a clear view over a distance of fifty miles was seldom possible. Everest
therefore introduced the use of heliotropes — mirrors reflecting the sun – for day working, and blue flares for night work. He also pioneered what he called ‘ray-tracing’ – fixed telescopes trained on the distant flares. The accuracy was now staggering. The difference between the Dehra Dun baseline as measured on the ground and as triangulated from a baseline on the great arc 400 miles away was
just 7.2 inches.