Stanford sextant

While handling and inspecting this carefully preserved sextant on a table at the David Rumsey Map Center, it was easy to forget the bitter winds and rocking decks which confronted marine astronomers trying to use such instruments to take celestial measurements at sea. William Bayly’s logbook from 1772 to 1774 describes how

fantastical sights of icebergs, whales, dolphins, penguins, and the Aurora Australis alternated with horrendous weather, including violent storms and snow, waves breaking over the decks, and poor visibility … strong gales & squally with a hollow trembling Sea

But perhaps sitting from this privileged position is befitting, since this sextant appears never to have been used.

Jesse Ramsden’s dividing engine massively reduced the labour involved in the production of the precision navigation instruments. It marked a sociotechnical solution to the long-standing problem of determining longitude at sea. The Ramsden sextant’s wide arc, reflecting mirror, and accurately engraved scale were marvels of precision engineering, capable of measuring celestial distances down to a sixtieth of a degree. Since it could be produced without artisanal competence, the sextant was far cheaper than its more technically advanced rival – the marine chronometer. And the sextant was a kind of social technology in another sense, too. It conveyed authority on ship, to maintain the sense of hierarchy that prevented disorder or mutiny. Yet the luxurious nature and pristine condition of this sextant indicates it was never purchased for use in navigation or social coordination at sea. It seems rather to have been intended as a show piece, standing as it does for Britain’s rising coalition of commerce, industry, and genteel science, defenders and prime movers of the late eighteenth-century empire.

The longitude problem

Research on the British empire too rarely acknowledges the importance of practical astronomy and navigation technology in securing imperial power at sea. On both naval and merchant ships, astronomers observing celestial objects using instruments such as astrolabes, backstaffs, octants, and sextants played a central role in discovering, charting, and claiming new territory for empire. Writing in 1576, the English mathematician Thomas Digges noted that there was ‘one great imperfection yet’ hindering the art of maritime astronomy – ‘and that is the wante of exact rules to know the Longitude … without the which they cannot truly give the place or situation of any coaste, Harborough, Roade, or Town, ne yet in saylinge discerne how the place they sayle unto beareth from them’.  Almost two hundred years later, surprisingly little had changed. By the mid-eighteenth century, one geographic coordinate at least was straightforward to determine: the backstaff and octant were readily available as instruments for celestial navigation, and with them astronomers could easily determine latitude by measuring the altitude of the sun or pole star above the horizon.  However, the apparent positions of these celestial guideposts do not change as the observer moves east or west. To determine their longitude, navigators had to calculate both local time (ascertained from latitude) and the simultaneous time at a reference point – the prime meridian at Greenwich.

Until a workable solution was found, navigators were forced to proceed by dead reckoning – charting a course by compass and judging currents by experience. This was an unreliable and dangerous method. Famously, the Scilly naval disaster of 1707 saw lost ships and over a thousand sailors’ lives lost. The longitude problem was thus a thorn in the side, for a nation which by the eighteenth century had come to define itself through public science, imperial commerce, and naval strength, and whose outposts had begun to span ever-farther stretches of the Atlantic and Indian Oceans. In 1714, following further losses to the British fleet, parliament passed the Longitude Act, which offered a £20,000 prize for a method which could determine longitude at sea within 30 minutes. The Act achieved its desired effect, inspiring two solutions to emerge as contenders. The first was John Harrison’s marine chronometer, a clock which could keep reference time at Greenwich. The second was Jesse Ramsden’s engine-divided sextant, a more affordable instrument, which with a nautical almanac could also determine longitude.

John Harrison’s H4 marine chronometer – described by Simon Schaffer as among the ‘charismatic megafauna’ of scientific instrument collections  – was a state-of-the-art solution to the longitude problem and was awarded the most prize money. Unlike pendulum clocks, its complex machinery could keep time at the reference point in Greenwich for long periods with remarkable accuracy while withstanding rough seas and bearing extreme variations in temperature, pressure, and humidity. The H4 was immediately heralded as a mechanical marvel, and has since been celebrated in popular histories. But these marine timekeepers had not yet solved the problem of determining longitude at sea in practice. Chronometers were expensive, and their fragility meant that several had to be carried together. Moreover, navigators remained sceptical of clockwork. As late as 1804, Andrew Mackay’s The Complete Navigator held that much ‘confidence cannot be placed in time-keepers, as their rate of going is so liable to be altered from the least accidental injury’.  

Like many navigators, Mackay preferred the celestial solution, which involved using sextants to calculate longitude by comparing measured lunar distances (the angle between the moon and certain prominent stars) with data from astronomical data reference tables (the nautical almanac was compiled from 1767 under the royal astronomer at the observatory in Greenwich). Where backstaffs and octants sufficed for measuring altitudes above the horizon, sextants enabled the measurement of lunar distance in two ways. First, their arcs measured one sixth of the circumference of a circle, permitting the measurement of wider angles. Since sextants reflected images from an index mirror onto a horizon mirror, the 60-degree arc could be used to read angles of 120 degrees. Second, their arcs had graduated scales precise enough to measure lunar distances down to a sixtieth of a degree. Modelling his design on Hadley’s octant, John Bird produced the first sextant accurate enough to measure lunar distances in 1759.  But the process of engraving scales with a beam compass was arduous, requiring weeks of skilled labour. For the celestial solution to the longitude problem to be practicable, it would be necessary to produce accurate and affordable devices in huge quantities.

Ramsden heralded the most promising solution to the longitude problem in 1774, with his dividing engine for cheaply manufacturing accurate sextants. By fixing a blank sextant frame onto the dividing engine’s wheel, its measuring scale could be engrave 2160 teeth cut at precise regular intervals, driven round by an endless screw. Ramsden’s machine, operated by unskilled workers and a foot pump, automated in minutes what it had taken weeks to do manually. As Allan Chapman has explained, ‘Jesse Ramsden turned the scientific instrument … into a cost-effective industrial artefact, … where high quality was made to cost less in real terms than ever before’. For this and other reasons, Mackay predicted that ‘the method by lunar observations will always claim the pre-eminence, upon this account, that the lunar tables are now brought to a very great degree of exactness, as also the method of constructing instruments proper for taking the necessary observations’. Like other mechanical engineers during the Industrial Revolution, the achievement of Ramsden lay in reducing the costs of production. His sextant made determining longitude at sea more affordable.

The Ramsden sextant was thus one social-technical solution to the longitude problem. But, as David Philip Miller argues, sextants were part of broader ‘longitude networks’: they ‘could be universalized in theory but individual determinations of longitude at sea were contingent acts reliant upon hardware (instruments, ships), software (methods, procedures, logs, charts, tables, outputs of land-based observatories), and wetware (the embodied skills, abilities, judgments and goals, of sailors, officers, hydrographers and their masters).’ The marine astronomer needed a nautical almanac, for the pre-computed calculations of predicted lunar distances overseen by astronomer royal Nevil Maskelyne in Greenwich, the centre of calculation, as they relied on the maps produced by hydrographers and surveyors. Within this network, the adoption of advanced navigational precision instruments was not straightforward. Still not everyone could afford a sextant, which was likely to break at sea. Miller points out that since all navigational techniques had their advantages and disadvantages, the best approach was to use them in combination. Due to the risk of damaging sextants, sailors often used cheaper instruments such as backstaffs and octants to measure latitude. Sextants were only used sometimes, to measure larger angles when precision was essential.

The Adams sextant

As the catalogue description states, the ‘9-3/8” Radius lattice frame sextant’ at the David Rumsey Map Center had a scale ‘almost certainly cut on a Ramsden engine’. The Board of Longitude had awarded Ramsden £615 for his engine, on the condition that he disclosed its workings to other instrument makers. George Adams, who produced this instrument, is not known to have had his own engine. It was typical for eighteenth-century instrument makers to have their octants and sextants cut on an engine made by Ramsden, Troughton, or Spencer, Browning & Rust, though this sextant lacks any trademark on its scale. 

Many suggestive details about the Adams family of instrument makers in London do survive. The instrument was made by George Adams the younger, whose shop at 60 Fleet Street was called Tycho Brahe’s Head – a reference to the Danish astronomer and nobleman whose observations using altazimuth quadrants introduced a new degree of accuracy to the astronomical sciences. Adams apprenticed under his father, who specialized in providing navigation instruments for the Board of Ordnance. He was one of hundreds of instrument makers in the metropolis whose products were traded across Britain, its provinces and colonies, and across Europe and the wider world. The Adams workshop functioned as a household, ‘some combination of apprentices, journeymen, employees, and family members’, enmeshed in networks of patrons and subcontractors such as opticians, metalworkers, and engravers. The Adams name was reputed for luxury, precise instruments. Adams Sr. boasted in 1746 of his products: ‘That their Exactness may be particularly attended to, I always inspect and direct the several Pieces myself, see them all combined in my own House, and finish the most curious Parts thereof with my own Hands’. The shop was also unusually diversified. For the Office of Ordnance, they produced gunner’s quadrants, perpendiculars, gunner’s callipers, theodolites, plane tables, and measuring chains; for George III, spectacular orreries, vacuum pumps, and the famous ‘philosopher’s table’. Otherwise, they were best-known for their microscopes and globes.

When Adams the younger took over the family business in 1772, the workshop seems to have struggled, as state budget cuts forced the Board to reduce their orders of instruments. John Millburn suggests this led Adams to writing, styling himself as ‘Mathematical Instrument Maker to His Majesty, and Optician to His Royal Highness the Prince of Wales’. Adams’s Description, use, and method of adjusting Hadley’s quadrant and sextant (1789) celebrated the improvement of ‘the art of navigation by the present method of finding the longitude, which enables the mariner to ascertain with certainty his situation on the unvaried face of the ocean’. Adams not only explains how to use his sextant, but also includes a detailed diagram, including an advertisement for the various navigational instruments available at his shop. Significantly, he suggested that this brass sextant was that ‘on the most improved plan’ – the priciest available, with a maximum cost of £15 15s, a significantly larger sum than a Hadley’s quadrant in mahogany for £2 2s.

Who would have purchased such an expensive sextant? There were a wide range of navigational precision instruments available on the London market, for a variety of income brackets and purposes. Opposite Adams on Fleet Street was the storefront for the famed instrument maker Benjamin Martin. But the instruments made by these fashionable workshops contrasted with the cheaper alternatives such as octants and wooden backstaffs still widely favoured among seamen who frequented shops at Wapping docks. Despite its high degree of technical precision, this instrument would be a liability at sea. At a price of over £15, it marked a major investment, especially when even a captain’s salary was not more than £400.

One possible answer is that such instruments were not just used for discretely technical purposes, but to mediate social relations and coordinate hierarchies at sea. Eoin Philips has studied the delicacy of hierarchies and complex division of labour on which astronomical and maritime fieldwork depended. The threat of mutiny was omnipresent, and instruments such as chronometers and sextants, which ‘have come to stand as symbols of rationality and enlightenment’, were vital for ship discipline. Phillips even argues that ‘the solution for discipline and visibility rested more on successful performance than it did on the functioning of the hardware itself’.  A telling feature of this sextant’s custom-fitted mahogany box, which also houses its various telescopic and optic accoutrements, is its keyhole.

While in ideal circumstances, junior seamen would respect the authority of the astronomer and officers who held such magnificent and valuable instruments, regimes of cultural signification were inherently unstable.  For many seamen, accustomed to the backstaff, complex precision instruments like sextants, or black boxes like marine chronometers, could be suspicious or even without value. Philips describes a mutiny against captain William Bligh on HMS Bounty’s voyages in the South Pacific during 1789, when the crew seemed to be content with a ‘quadrant and compass’, allowing Bligh to keep his sextant. Such intriguing instruments could also arouse unwanted attention, and enter into an entirely alien regime of cultural signification. James Cook entered a fraught exchange with Bora Bora islanders in 1777:

on the evening of the 22nd a sextant was taken from Bayly’s observatory. A dramatic performance was in progress: Cook put a stop to it and again threatened punishment worse than that at Moorea if both sextant and thief were not delivered up. The criminal, pointed out sitting calmly in the audience denied the crime; Omai flourished a sword and said he would run him through; the chiefs all fled; Cook, a little in doubt, sent the man on board the ship and put him in irons. Omai, by threats and promises wormed a confession out of him, and in the morning the sextant was found unharmed where he had hidden it. He appeared to be ‘a hardened Scounderal’, says Cook; ‘I punished him with greater severity than I had ever done any one before and then dismiss’d him.’ That is, this time the man was both shaved and lost his ears.

An instrument as expensive and fine as this was probably never purchased, or even produced, for use in navigation and social coordination at sea. This sextant has suffered none of the wear and tear one might expect from field work, with a still-pristine lacquered brass finish. Though the complex telescope tubes, horizon glasses, and moveable shades of sextants were acutely vulnerable to breakage and disrepair at sea, only one of the telescopes is slightly cracked. It is thus likely that this was a show piece. An optical and mathematical instrument for practical observation, the sextant also became a luxury item, like other fashionable technological trinkets such as magic lanterns. Indeed, the Adams family produced many such toys, which made business as an eighteenth-century instrument maker profitable. Given, as Alexi Baker argues, that such toys carried different types of meanings – ‘telescopes and microscopes were used to suggest qualities including insight and wisdom [and] globes often gestured towards worldly power and knowledge’ – it is worth investigating what crystallised meaning this Adams sextant might have acquired as a showpiece.

A gentleman’s toy

The sextant belonged to a distinctive class of toys and trinkets, in that it was designed for a distinctly practical purpose: to measure longitude at sea with exceptional precision, in a box designed to protect the instrument from the vagaries and dangers of fieldwork. This fact should not obscure, but rather help clarify its cultural signification: it was because the sextant was known as a major technical advancement, an instrument of empire, that it could convey meaning as a showpiece. As Adams suggested in his description of the object, ‘in every instance of the progress of science … we may trace some of the steps of that vast plan of Divine Providence … by the advancement of knowledge, the diffusion of liberty, and the removal of error, that truth and virtue may at last shine forth in all the beauty of their native colours’. While all expensive scientific instruments could confer an impression of learning and wealth onto their purchasers, the sextant in particular resonated with the sense in late-eighteenth-century London that gentile science could enable Britain’s domination over vast geographies.

As Schaffer argues, sextants fit into both ‘narratives of bureaucratic administration and calculated rule as well as to those of ingenious skill and heroic belief’. This relation suggests perhaps the most significant aspect of the sextant’s meaning: ‘Charisma had somehow to become routine.’ The dramaturgical persona of London’s premier instrument inventor Ramsden had been routinised by his dividing engine. Traditionally, trustworthiness of precision instruments was associated with the skill and reputation of its maker. As Nevil Maskelyne had put it, ‘I was secured from any errors in the construction of the quadrant, by the known skill of the artist’. Ramsden’s dividing engine undermined the logic of artisanal credibility. The reliability of a mechanically-engraved sextant lay less in its maker’s embodied skill, than in its maker’s access to cutting-edge machines.

As Linda Colley argues, following the Seven Years War, Britain’s expanded territorial empire demanded new magnitudes of investment in administrative machinery. When faced with mutiny, Captain Bligh was most concerned with securing his paperwork to prove accurate accounting: ‘Without these, I had nothing to certify what I had due, and my honour and character would have been in the power of calumny without a proper document to have defended it’.  The heroic astronomer stood for an emerging ideology of empire, which predicated credibility on routine precision. And it is in this convergence of cultural signifiers – heroic leadership and rational, bureaucratic administration – that an emerging ideology of imperial rule was expressed, in both the administrative reforms introduced by the India Act (1785), and subsequently in the Great Triangulation Survey of India from 1803. The Adams sextant was a resonant instrument of techno-political imperialism, manifesting attributes such as precision, exactitude, and credibility, which were made possible by centralising the organisation of calculation production in the metropole.

For several decades, scholars in science studies have investigated broken instruments to opposed a tendency in historiography and museology to represent tools as unproblematic symbols of disembodied progress. But biographers of pristine scientific instruments may also see their objects as as the material remnants of the social realities of knowledge production and scientific practice. As Alexi Baker’s recent work shows, representing immaculate scientific instruments as self-contained tools of progress, far removed from the messy realities of field work, was also a contemporary phenomenon. Eighteenth-century trade cards displayed instruments as ‘idealized and unproblematic tools’, as is also the case for Adams’ engraving of his own sextant. The garbological impulses of critical theory and science studies demand us to problematise not just damage, but spotlessness.

Whether exhibited in the display cabinets of country houses, or displayed in the shop windows of the metropolis, unworked tools such as this sextant could convey a symbolic distinction between an imperial ideology of technical progress and genteel astronomy, and its troublesome corollary – the grubby materiality of fieldwork and the mechanical arts. The administration of maritime empire was idealised as unproblematic if rational, conducted by heroic gentlemen at sea. The mathematical and optical instruments which enabled precision, despite their provenance in the workshop and their intended application in the field, when finely crafted and kept out of their assumed context, became urbane symbols of the polite science of imperial geography. Such a distinction was of course always delicate. As Katy Barrett puts it, ‘“the longitude” articulated a problematic space between polite and impolite science, which made it a useful concept with which to negotiate wider contemporary social boundaries’ in late eighteenth-century London.



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