Map of a Nation (16 page)

The first national triangulation, or ‘trigonometrical survey’, in Britain had been proposed in the years directly following the instigation of the French one. By the end of 1681 a cartographer called John Adams had measured a twelve-mile baseline on King’s Sedgemoor in Somerset, with the backing of the newly founded Royal Society. But by 1688 Adams had complained to the Archbishop of Canterbury of the lack of finances that meant the project had folded. Similarly lacking the necessary instruments, personnel and finances, William Roy had not based his Military Survey of Scotland on a
trigonometrical
survey either, and consequently there had been an accumulation of errors in that map’s measurements. As this suggests, the principal purpose of triangulation was to form an accurate skeleton for a map of a large piece of land, a structure around which the finer details of the interior landscape could be arranged. It could also be used to create a simple chain of triangles, running north to south, with which to measure a meridian arc. Triangulation was the surveying technique
du jour
during the Enlightenment. Measurements taken from the ground itself could be distorted by imperfect measuring chains, bogs and thorny undergrowth, roads and fences, or interfering locals. But triangulation promised to realise the Enlightenment ideal of perfect measurement. Because each corner of each triangle was also at the corner of further triangles, any errors could be quickly identified. And apart from the initial ground-level measurement of the baseline, the surveyor’s sight lines seemed to shoot, unimpeded, above the landscape, ricocheting smoothly from steeple to steeple, summit to summit. As we shall see, these aspirations to perfection were not quite so easily realised, but the technique was
nevertheless
more sophisticated than any other.

Jean Dominique Cassini began by using triangulation to measure his meridian arc through France. Before long he had expanded this project to attempt a complete national map. Thanks to its unprecedented accuracy and scope, this became the first survey of its kind in the world, and a model for all future national maps based on triangulation, including the Ordnance Survey. The French mapping project would occupy four generations of the
Cassini family: Jean Dominique, his son Jacques (known as Cassini II), his son César François Cassini de Thury (Cassini III), and
his
son, again called Jean Dominique Cassini (Cassini IV). In 1756 the first of the eventual 181 sheets of the Cassinis’ national map of France was published. Known
variously
as the
Carte de Cassini, Carte de France, Carte de France de Cassini
, or
Carte de l’Académie
, the endeavour sealed the family’s fame. The Cassinis’
achievements
in the fields of astronomy and map-making were such that their name is commemorated now by a host of memorials: the 24101 Cassini asteroid, lunar and Martian craters named Cassini, a mathematical curve called the Cassini Oval, the Cassini Web Server and a British publisher of historic maps named Cassini.

 

B
Y
O
CTOBER
1783 the third generation of the Cassini dynasty, in the shape of César François Cassini de Thury, was in charge of the Paris Observatory and overseeing the progress of the
Carte de Cassini
. It was then that he approached the British with the idea of verifying the precise
longitude
and latitude of the two royal observatories at Paris and Greenwich. But whereas English astronomers typically preferred to discover these positions by treating the stars as celestial compasses, Cassini de Thury recommended eschewing such ‘positional astronomy’ in favour of using triangulation to discover longitude and latitude by ‘joining up’ the meridian arc that bisected Paris with the Greenwich Observatory. His motives for suggesting the project were manifold. The check on Paris’s longitude and latitude would confirm the accuracy of the
Carte de Cassini
. And such a ‘junction’ between the Greenwich and Paris observatories would put global navigation on a firmer footing. Since 1767, Britain’s Astronomer Royal Nevil Maskelyne had been compiling an annual collection of tables of astronomical
observations
made at Greenwich, known as the
Nautical Almanac
. These tables allowed sailors to determine their longitude at sea, thus avoiding shipwreck and disorientation. A miscalculation of Greenwich’s position therefore
jeopardised
the safety of mariners across the globe. And there were other merits to the project too. The extension of the French meridian arc a few degrees
north would contribute further knowledge about the precise shape of the earth, a question that continued to trouble geodesists up until the twentieth century. Finally, in the wake of almost a century of intermittent hostilities between France and Britain, a ‘connection’ between ‘the two most famous observatories in Europe’ could forge a reconciliatory bond.

France and England had long been one another’s arch-rivals, scapegoats and punchbags. By 1783, a prolonged series of wars had repeatedly set Britain against its neighbour over the course of a century: the War of the Spanish Succession, the War of the Austrian Succession, the Seven Years War and the American War of Independence, not to mention the Jacobite rebellions that had rocked Britain and Ireland between 1688 and 1746. There was an entrenched cultural hostility between the Protestant island nation and Catholic France. The English considered the French to be
effeminate
, debauched, weak and seduced by fashion and luxury. They were thought to be the diametric opposite of the archetypal Englishman: ‘John Bull’, the hard-working, honest, down-to-earth, beef-eating, beer-swilling patriot. Much of this xenophobic hostility was expressed through culinary metaphors. The French called the English ‘les rosbifs’, and considered them crass, uncultured and bigoted. The English referred to the French as ‘frogs’, after their notorious penchant for frogs’ legs, and they ridiculed the
gastronomic
affectations behind their ‘fricassees’ and ‘ragouts’. In the face of this deep-rooted nationalist animosity, collaboration and communication between British and French scientists continued throughout the eighteenth century, but they rarely remained entirely free from cultural antagonism.

When Joseph Banks shared Cassini de Thury’s proposal with a number of Royal Society fellows, many interpreted it as an enormous national affront. How dare the French question whether the English were entirely certain of the position of their own observatory. It was the Astronomer Royal Nevil Maskelyne’s
job
to use the stars to ascertain precisely where he was on earth. Charles Blagden, secretary to the Royal Society and Banks’s right-hand man, was sceptical about the French astronomer’s claim for the superiority of
triangulation
over astronomy. ‘I believe that it is not strictly the case,’ Blagden wrote cautiously, ‘and that occultations of fixed stars by the moon, carefully observed at both places, would give their differences of longitude nearer
than any actual measurement.’ A journalist in the
Annual Register
huffed that Cassini de Thury’s claim for the uncertainty of Greenwich’s location was made ‘without sufficient reason’. Maskelyne was also shown the
memorandum
, so ‘that you might consider it fully and at your leisure’. Although he was asked to word a formal response to the French geodesist, Maskelyne was too piqued to reply. A small, marbled notebook in Greenwich Observatory shows that he actually instigated his own secret experiment to measure the
longitudinal
difference between the two observatories, using chronometers, hoping to prove Cassini de Thury’s surveyors wrong.

But Joseph Banks was not so offended by the French proposal. He
considered
Cassini de Thury’s approach ‘as doing honor to our scientific character’. Banks passed it on to his great friend William Roy, whom he knew was considerably better qualified to judge its merits. Roy himself was an enthusiastic advocate of triangulation. He had spent much of that summer measuring beneath ashen skies a baseline of just under one and a half miles in central London, extending from the middle of what is now Regent’s Park, to Black Lane, a street north of St Pancras Station (now buried beneath railway yards). In the wake of the rejection of his proposal for a ‘General Military Map of England’, Roy had decided personally to take Britain’s poor state of cartography in hand. Ultimately, he wanted to use this baseline as the backbone for a triangulation around London, which he hoped would ascertain the longitude and latitude of certain important locations, including Greenwich Observatory.

When Roy received Cassini de Thury’s memorandum shortly after his own baseline measurement, he was surprised and delighted ‘that an
operation
of the same nature, but much more important in its object, was really in agitation’. Roy foresaw that the proposed triangulation between Paris and Greenwich would be ‘the first of the kind, on any extensive scale, ever undertaken in this country’. But although Cassini de Thury played up the scheme’s value in cementing amicable international relations, Roy was
principally
excited by what it had to offer Britain. He saw the triangulation as the basis for the ‘accurate Survey of the British Dominions’ of which he had dreamed for so long. Roy promised that the proposed ‘French Connection’ would ‘redound to the credit of the Nation’.

 

S
IX MONTHS AFTER
Cassini de Thury’s note had landed on Joseph Banks’s breakfast table, William Roy found himself on Hounslow Heath, to the south-west of London. Once George III had approved a sum of
£
2000 for its expenses, the 58-year-old Scot had been chosen to direct the British side of the project under the Royal Society’s auspices. The King was glad to extend an amicable hand to the French
savants
in this brief moment of peace, and to further the cause of British science. Now Roy’s first task was to measure a baseline, and he knew the exact spot. He had been fantasising about potential baselines since 1766, when he had originally thought that a base in ‘one of the open level Counties, such as Cambridgeshire or Wiltshire’, would be an ideal foundation for a national survey. But these locations were clearly unsuitable for a measurement between Paris and Greenwich. So Roy wrote to Banks that ‘in all the Tours I have made, no place, at least near the Capital, seemed to me so proper for the measurement of a Base as Hounslow Heath’.

In Roy’s time, the Heath encompassed a vast stretch of land. Now it is reduced to a small golf course, just over a mile wide: a meagre piece of grass north of Feltham that gasps for air amid the frenzied arteries of the A315, A314, and A312 roads. The old Hounslow Heath is now hidden under Heathrow Airport, buried beneath the unlovely roads that run between Hampton Hill and Hatton Cross, and swallowed up by the suburban
housing
and industrial estates that populate North Feltham, Hanworth and Hampton Hill. Roy, however, saw in the old Heath ideal surroundings for the beginnings of the Paris–Greenwich triangulation. The Heath was perfect for the triangulation’s baseline for the same reasons that it makes an ideal home for an airport today. ‘Because,’ Roy explained, ‘of its vicinity to the Capital … its great extent, and the extraordinary levelness of its surface, without any local obstructions whatever to render the measurement
difficult
.’ Heathrow’s barbed-wire perimeters, pavement-free roads and cramped tunnels put the site of the old Heath almost completely out of bounds for the pedestrian trying to follow in Roy’s footsteps. This was one of the least
beautiful
hikes that I undertook in the course of researching this book.

But even in Roy’s day, Hounslow Heath was not particularly savoury. Ridden with thorny scrub, ant hills and gravel pits, it was notorious for the highwaymen who plagued its internal paths. The Heath was also where convicted criminals came to rest: bodies suspended from gibbets were silhouetted against the horizon. Although attempts were made to gentrify the area in the 1780s, many despaired of success. The
World and Fashionable
Advertiser
reported despondently that improvers faced ‘natural obstacles at every turn – a clay soil – a confined boundary – bad country beyond it – and no collateral idea from contiguous objects, but what is gloomy and disgusting! – The Heath of Hounslow, with all its gibbets and powder mills!’