The year is 1763, the ink has barely dried on the Treaty of Paris, and already France is ruminating its defeat. The Seven Years’ War had pitted the Gallic nation and its allies against the kingdoms of Great Britain and Prussia, extending as far as the warring countries’ colonies as it escalated into the first global conflict. France had emerged weakened in Europe, and had lost much of its influence in North America and the Caribbean. Its army had been routed, its naval fleet decimated. Meanwhile, across the Channel, Great Britain was expanding its colonial power, “ruling the waves” thanks to the strength of the Royal Navy. In the wake of the Seven Years’ War, the theatre of operations had effectively shifted to the colonies, the new zones of influence with riches to conquer and untold opportunities for trade. More than ever, command of the oceans and maritime routes was of vital importance.
A hefty reward
First, though, a problem had to be resolved: how to plot longitude when navigating in the vastness of the ocean. By taking sightings of the sun and stars, sailors were able to reckon a ship’s position, but without a sufficiently reliable timepiece to precisely measure the time taken to sail between two points, ships were in constant danger of drifting off course and becoming shipwrecked on the rocks that appeared in their path. Captains were in the habit of taking on board a sundial mounted on a compass, but the results were all too approximate. When in 1707 Sir Cloudesley Shovell ran a squadron of four ships onto the rocks of the Scilly Isles, losing two thousand men, this was the last straw: in 1714, the British Parliament passed the Longitude Act which offered a prize of £20,000 – a colossal amount – “for such person or persons as shall discover the longitude at sea”. Conditions stipulated that the calculation should be accurate to half a degree (around thirty nautical miles) after forty days at sea. The Académie de Paris offered a similar prize four years later.
Watchmaking’s greatest minds set about the task with, in the background, centuries of rivalry between the British and the French. History tells us that the solution was finally discovered not by a clockmaker but by a carpenter, John Harrison. After twenty years and several clocks, each more precise and reliable than the last, in 1759 Harrison presented his now famous H4, an extraordinary marine chronometer resembling more a large pocket watch, measuring thirteen centimetres in diameter and weighing one and a half kilos. During a sea trial to Jamaica in 1760, Harrison’s chronometer fulfilled all requirements, reaching destination just five seconds slow (75 seconds after rate correction). Still, Parliament and the Board of Longitude were reluctant to award Harrison the £20,000 prize, claiming the result was a fluke, and that the H4 was impossible to reproduce in number. It would take a further twenty years, the construction of a new chronometer, the H5, and the intervention, at his request, of King George III before Harrison was given the acknowledgement he was due. Even then, he received only half the stipulated amount, in 1773, by which time John Harrison was eighty years old. He died three months later…
King Louis XV of France sent Ferdinand Berthoud to meet with John Harrison and uncover the secrets of his H4.
A well-guarded invention
Despite Parliament’s refusal to recognise the H4’s merit in solving the problem of longitude at sea, news of Harrison’s chronometer and its extraordinary performance had spread like wildfire in horological circles. And as no prize had been awarded, the competition remained wide open. Now that peace had been agreed between France and Britain, exchanges could resume between their respective scientific communities. A delegation composed of the watchmaker Ferdinand Berthoud, then aged thirty-six, the mathematician Charles Camus, and a thirty-one-year-old astronomer, Jérôme Lalande, was sent to London. One of its missions, at the behest of King Louis XV, was to meet Harrison and uncover the secrets of his H4. Unfortunately for the French, Harrison understandably refused to meet with Berthoud – who three years earlier had published a treatise on the construction of a marine clock (“Mémoire sur les principes de construction d’une Horloge de Marine”) – and was even less inclined to disclose the inner workings of his H4. Undeterred, Ferdinand Berthoud, who on home soil was in competition with Pierre Le Roy, inventor of the detent escapement, continued his research and built his Horloges de Marine No2 and No3; the latter was presented to the Académie Royale des Sciences. They were followed by No6 and No8. During its sea trial in 1768 to Saint-Domingue aboard the Isis, Berthoud’s Horloge de Marine No8 also met the requirements of the Longitude Act, that is precision to within half a degree. This was a first for France’s Royal Navy, and brought recognition for Ferdinand Berthoud who throughout his life would be welcomed into royal circles.
The question remains, did Ferdinand Berthoud gain access to the H4? The astronomer Jérôme Lalande who accompanied him is known to have met John Harrison on several occasions, as noted in his journal – certain pages of which have mysteriously disappeared. Did Lalande succeed in convincing Harrison to reveal details of the H4’s mechanism which he then reported back to Berthoud? Also, Berthoud was acting on the King’s behalf, and was therefore at liberty to pay for information. Then there is the disconcerting similarity between Berthoud’s N°3 clock and Harrison’s H4. Nor can we overlook the role of Charles Pierre Claret de Fleurieu, an ensign on the Isis who had fought the British during the Seven Years’ War, and who was rumoured to be an agent for the king, charged with spying on the Perfidious Albion and its inventions. What’s more, Fleurieu had studied horology with Berthoud, and the two men maintained a close alliance against a backdrop of rivalry with Pierre Le Roy. So many questions without answers, and yet we can safely say the greatest minds were involved in the construction of a marine chronometer that would bring wealth and power to nations!