The Great Arc

by John Keay

  To wear flannel next the skin and on the feet, more particularly while asleep; to lie high from the ground, and keep a fire in the house or tent during the night; not to walk out while the grass is wet with dew; to smoke tobacco while the air remains damp; and to take regularly as much exercise as the strength will, without feeling fatigue, admit of.

  Should the traveller, despite following these injunctions to the letter, contract a fever, the cause was probably ‘an enlargement of the spleen’. The only hope then was ‘hot bathing, keeping the body bare, and taking continued and even fatiguing exercise’. That and, of course, frequent induction of those panaceas of Anglo-Indian medicine, ‘opium, a moderate quantity of the best wine, and a free use of spices’.

  Unlike George Everest’s reports, Lambton’s do not dwell on such dangers. The misfortune of a lost flagman goes unrecorded and the need for extensive tree-felling is merely a ‘difficulty’. Tigers are never so much as mentioned; and Lambton himself seems not to have suffered a day’s illness in his life. Like 90 per cent of his fellow-countrymen in India he almost certainly caught either malaria or dysentery or both; but he says nothing, perhaps because he saw no need to advertise the fact or perhaps because he feared giving the authorities a pretext for curtailing his labours.

  It is known, though, that his men were not immune and that his second assistant was indeed overtaken by the ‘Malabar ague’. Nearly dead (from the cure if not the ague), he was invalided home. But India’s loss became England’s gain; for Henry Kater would go on to become one of the most distinguished physicists of his age, a leading light of the Royal Society, and the inventor of ‘Kater’s pendulum’ and the prismatic compass. In 1823 he would send his old boss news of a miniaturised theodolite which he had just designed; it was as accurate as their ‘Great Theodolite’ but could fit in a box no bigger than a suitcase and be carried by one man. Sadly Lambton was himself in a box beneath the turf of Hinganghat by the time the letter arrived.

  Instead of filling his reports with human detail, Lambton stuck to science. His two stations atop the Western Ghats gave heights above the level of the sea as measured back at Madras of 5,583 and 5,682 feet. From that fifteen-foot slope to the grandstand at the Madras racecourse he had carried his elevations across a subcontinent and up into the clouds. That these were indeed the first precisely measured peaks in India became clear when he continued his triangles down to the coast. Sea-level at Mangalore on the Malabar coast of the Arabian Sea as deduced from that of the Bay of Bengal on the opposite side of the peninsula was found to differ from its actual level by only eight feet. Given the variable and still uncertain properties of refraction, and given the tidal variations, this was as satisfactory a proof of the accuracy of Lambton’s vertical angles as the 3.7-inch differential in the Bangalore base had been of his horizontal angles. It was such irrefutable logic which the scientific establishment in Europe would find so painfully wanting in Henry Colebrooke’s claims for the height of the Himalayas.

  A more surprising discovery was the revelation that the Indian peninsula had shrunk. Against then current maps which, largely based on coastal surveys and astronomical reference, supposed a width of around four hundred miles, Lambton’s survey conclusively proved that it was only 360 miles from Madras to Mangalore. A coastal strip of some ten thousand square miles was thus consigned to the Arabian Sea. Thanks to Lambton, British India sustained its greatest ever territorial loss. Fortunately this result mirrored almost exactly that obtained in France when in the seventeenth century a survey had found that Brittany had been represented as protruding over sixty kilometres further into the Atlantic than it actually did. At the time Louis XIV had complained about his surveyors having ‘cost me a large part of my territory’. But the precedent thus set exonerated Lambton from similar censure, indeed served to confirm the value of his work.

  No base-line was measured on the Malabar coast. The onset of the monsoon in 1805 forced Lambton back to Bangalore and, although he returned to the west coast in 1806, circumstances again prevented the assembly of men, chains, tripods and coffers, let alone the extensive ground clearance, that was essential for base measurement. He regretted the failure but, having completed the first longitudinal arc across the peninsula, he now concentrated on his latitudinal measurement, or great arc of the meridian. (Confusingly, measurements which follow a line of latitude are known as ‘longitudinal’ because it is degrees of longitude which they traverse and measure – and vice versa.) With the Bangalore base as its starting point, the triangles of what Lambton later called the ‘Great Indian Arc’ were extended north about a hundred miles to where British territory ran up against that of the independent Nizam of Hyderabad, and then south towards Cape Comorin (Kanya Kumari) at the tip of the subcontinent. The next base-line was in fact measured on the Great Arc near Coimbatore, about 140 miles south of Bangalore, in 1806. In its length of over six miles the difference between the triangulated measurement carried from Bangalore and the actual measurement on the ground came to 7.6 inches.

  Another long stride of similar distance would carry the arc down to Cape Comorin in 1809; and another base-line measured near Tirunelveli (south of the ancient capital of Madurai) would produce an equally satisfactory result. But any celebrations over the successful completion of the southward arc were marred by anxiety. For in the meantime, with a particularly sickening crash, disaster had struck. What even the phlegmatic Lambton would concede to have been a catastrophic accident had thrown the whole enterprise into jeopardy.

  The trouble had begun amongst the sea of waving palm fronds which blanketed the flat delta region of the Kaveri river east of Tanjore (Thanjavur) in southern Tamil Nadu. In late 1807 Lambton had left the Great Arc to conduct a parallel triangulation down the east coast from Madras. This meant in effect continuing that short arc measured in 1802 to establish the length of a degree as a preliminary to his whole survey. The government was now urging the need for a web of triangles covering the whole peninsula as the basis for a map rather than just the chains of triangles, running north – south and east – west, which promised most to the geodesist. Extending a series down each coastline and then filling in the triangles between these and his Great Arc looked to be the best way of meeting this demand. Hence Lambton’s progress south from Madras in 1807–8.

  All went well until he ran out of hills and droogs in the wide and tree-choked Kaveri delta. Visibility through the coconut palms was impossible without a major felling programme, and the construction of towers was as yet considered an unthinkable expense. Tamil Nadu is, though, famous for its temples. The Tamil temples are in fact the largest in India, and although their numerous shrines and halls may not be especially lofty, they are usually contained within high walls whose gateways, or gopurams, support magnificent stacks of sculpture which soar above all else, palm trees included. The solution to Lambton’s problem was spectacularly obvious.

  There were good precedents for using ecclesiastical buildings. In France surveyors had scaled the towers of several cathedrals including Notre Dame in Paris and, en route to a junction with William Roy’s triangles across the English Channel, that of Rouen in Normandy. Roy himself had measured angles from a platform erected around the ball and cross on top of the dome of St Paul’s Cathedral in London; and to obtain a flat working area on the spire of Norwich cathedral, he had actually removed its topmost courses of stonework. No such liberties could be taken with temple structures in India. The temples’ brahmins had to be carefully and generously handled. Yet the riot of sculpture made climbing easy, and from atop a gopuram the level terrain beneath the sea of coconut fronds meant excellent visibility.

  Hopping from gopuram to gopuram, the survey continued south, but in 1808 even the temples ran out. From that of Kumbakonam Lambton had sighted to the west the tower of Tanjore’s Rajarajeshwara temple. He now decided to abandon southward progress and to carry his triangles inland to link up with the Great Arc by way of Tanjore.

  The Tanjore Rajarajeshwara,
or Brihadishwara, is dedicated to Lord Shiva and was built in the early eleventh century by the great king Rajaraja I, the founder of a south Indian empire whose power reached from Sri Lanka to Malaya and Bengal. Unlike later temples, its gopurams are modest, but the main shrine itself is graced with a pyramidal colossus of stonework, 217 feet high. It is in fact the loftiest and, to many minds, the loveliest temple tower in all India. Here was a unique eminence in every way worthy of Lambton’s unique instrument. With ropes and pulleys the lascars were soon hauling the Great Theodolite to its summit.

  The topmost capstone of a south Indian temple tower is sometimes called an amlaka, because of its round and often ribbed resemblance to a myrobolan fruit. That of the Rajarajeshwara is more dome-shaped and is carved from a single block of granite, over a hundred feet in circumference and estimated to weigh eighty tons. It is thought to have been originally manoeuvred into its exalted position by way of an earthen ramp specially constructed for the purpose and all of four miles long. Compared to this feat, the hoisting of a mere ten hundredweight of machinery looked simple. The pulleys were attached to the amlaka; the vast paved courtyard in which the temple stands left ample room for the rope-pullers to manoeuvre; and to keep the theodolite clear of the statuary a guy rope was attached and then probably lashed round one of the pillars of the courtyard’s cloister, as to a bollard.

  It was this guy rope which either slipped or, according to George Everest’s later account, actually snapped. The theodolite, disregarding such niceties as plumb-line deflection, swung smartly towards the vertical and there met the sloping sides of the pyramidal tower, knobbly with sculpture, in a splintering crash. Luckily the instrument was still in its box, or it would have been flattened. As it was, the box took the brunt of the impact and was shattered by the statuary as the protruding tangent screw of the instrument’s three-foot circle punctured the packing. The screw sheared and the great circle or dial, so perfectly cast, so minutely calibrated, and so lovingly handled, was left as bent as a bicycle wheel after a head-on collision.

  Lambton seems to have accepted full responsibility. ‘The high mind of the late Superintendent [i.e. Lambton] could not brook the idea of being reproached for this accident,’ recalled Everest, and ‘the circumstances of the case were never, I believe, officially brought to the notice of Government.’ Although the instrument was valued at £650 (to which sum two zeros may be added for a modern approximation), Lambton ordered a replacement from England at his own expense and then retired along with the mangled original to the military workshops at nearby Trichy.

  Any person but my predecessor [writes Everest] would have given the matter up as absolutely desperate; but Colonel [Captain at the time] Lambton was not a man to be overawed by trifles, or to yield up his point in hopeless despondency without a struggle. He proceeded to Trichy … [and] here he shut himself up in a tent, into which no person was allowed to penetrate save the head artificers.

  It was the height of the Indian summer, the same summer which, in the far north, found a delirious Robert Colebrooke dreaming of cool Himalayan peaks as he watched the monsoon clouds build above the Ganges while the sacred river bore him downstream to his death. Lambton, like Achilles, never budged from his tent. But far from sulking, he fussed over his beloved instrument through the dog days and sweat-soaked nights like a doctor fighting for the life of his patient. Outside his men waited, their Survey stalled if not permanently halted and their employment in doubt. Everest continues:

  He took the instrument entirely to pieces, and, having cut out on a large flat plank, a circle of the exact size that he wanted, he gradually, by means of wedges and screws and pullies, 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 shape. The radii, which had been bent, were restored to the proper shape and length by beating them with small wooden hammers.

  Everest was profoundly impressed by this whole saga. Although relying on hearsay, he would tell the story often, and elsewhere says that the repair work took six months, not six weeks. He also suggests that the restored theodolite, though usable, never again inspired quite the same confidence. Lambton appears to have been satisfied with it and was still relying on it when Everest joined him nine years later. But Everest would contend that the main triangulation of the next section of the Great Arc as it edged north into Hyderabad would suffer from the instrument’s failings.

  Finding fault with men, as with instruments, came easily to George Everest. It would not be out of character for his criticisms to have been a way of trumpeting the higher standards of his own work without inviting the accusation of having personally disparaged his distinguished predecessor. Lambton, on the other hand, had no time for such games. His only recorded criticisms were reserved for those in authority who attempted to curtail his work. Colleagues and subordinates he invariably supported and they revered him without exception.

  Moreover it is unthinkable that he, of all people, would have made do with a instrument which he knew to be other than as perfect as humanly possible. If his later work was found to be to a less exacting standard, the explanation lies in his increasing willingness to delegate the actual triangulation to his assistants, Everest amongst them. This was partly dictated by the need to train a successor and partly so that he himself could concentrate on the more arcane calculations and observations vital to geodesy.

  Now perhaps in his late forties and greatly encouraged by recent appreciations of his work from Sir Nevil Maskelyne, the Astronomer Royal in London, Lambton was no longer the tongue-tied stranger from the backwoods of New Brunswick. He was still a slave to science, still immersed in mathematical abstractions, and still largely indifferent to the social wheelings and professional dealings of his fellow officers. But ten years in India had given him the confidence of a man who had finally discovered his life’s purpose. He now purchased, as was standard practice, the rank of Major and, when not in the field, set up house and home on the coast. He even started a family. But if less aloof, he remained just as elusive. While colleagues would certainly have preferred to live in society amongst the British in Madras, Lambton had chosen to live in sin amongst the French in Pondicherry.

  FIVE

  The Far-Famed Geodesist

  Lambton’s reports, as well as lacking the personal detail which might redeem their Spartan syntax, are also extremely light on dates. Numbers and calculations relevant to his work abound, but the simple digits of day, month and year are omitted. If Everest was later confused about whether the repairs to the Great Theodolite had taken six weeks or six months, it may be because Lambton himself had never bothered to record their completion.

  We do have a note of how long was spent in measuring each of his base-lines; additionally we know on which nights he conducted astronomical observations, the dates in this case being an essential part of the data. But how many days he spent fixing any of his trig stations is anyone’s guess. As with the mystery of his age and birth, Lambton seems to have rejoiced in obscuring the record. Geodetic formulae are known as ‘constants’; to a mind obsessed with pinpointing the permanence of place, time’s insidious trickle may have been anathema. Or perhaps covering his tracks through the years was a deliberate subterfuge, another dimension of a retiring and elusive persona.

  In 1809, after the catastrophe in Tanjore, Lambton’s triangulation of the extreme south was overtaken by a smart piece of British aggression against the Raja of Travancore in what is now the state of Kerala. The Survey’s presence proved only a minor provocation in what the British historian Sir Penderel Moon calls ‘the least justifiable of the many questionable transactions by which British power in India [was] acquired’. During the few weeks which the affair lasted, Lambton, swapping geodesy for gunnery, served as a military engineer. Then, after measuring his base-line at the southernmost extension of the Great Arc, he retired to Pondicherry to work on his calculations and produce the map of peninsular India which would embody them.


  Pondicherry then, as now, was an undemanding billet. The tree-lined corniche, the stucco villas, and an air of social and ethnic fraternité recalled its golden age in the eighteenth century as the crucible of French ambitions for an eastern empire. Technically it was still the capital of French India. But the British had held it for fifteen years and would continue to do so until after Napoleon’s defeat. With a population of only 25,000 it was already a seedy backwater compared to bustling Madras a hundred miles up the coast. Lambton chose it because its cosmopolitan climate appealed to his assistants, few of whom had been born in Britain, and because it was better suited both to his retiring nature and to his greatly changed domestic circumstances.

  When and where he had met the mysterious ‘Kummerboo’ is not known. Her name sounds vaguely Hindu but in Lambton’s will she is described as ‘a Moor’, or Muslim. An officer’s loves were seldom transparent and in this Lambton was no exception. According to John Warren, Lambton ‘appeared to disadvantage in mixed companies, and particularly in the company of women’. On the other hand Everest, not much of a ladies’ man himself (although also capable of surprises), calls Lambton ‘a great admirer of the fair sex’. Presumably it was the trussed and trivia-minded British memsahibs whose company showed him to disadvantage, ‘not one of them,’ according to Richard Wellesley, ‘decently good-looking’. Their shyer local sisters, Kummerboo amongst them, must then have been the fair ones – and the not so fair ones – who drew Lambton’s admiration.