1767 - Trial of Pierre Le Roy's Chronometer

After having tackled the building of a marine watch in 1756, Pierre Le Roy, 50 years old, has reached a new step last year. It is said that the chronometer he presented to the Académie Royale des Sciences is as precise and reliable as famous Harrison's H4.

¤ Le Roy already invented the detent pivot escapement, or detached escapement, that he presented the Académie in 1748, the temperature-compensated balance by using bi-metallic components, and lately the isochronous balance spring through the discovery of the right precise length.

¤ As everybody knows, the invention of the balance spring is a dual invention of Robert Hooke (†1703) and of Christiaan Huygens (†1695) in 1657, but the first completed watch is Huygens' one.

The chronometer seems so promising that François César Le Tellier, marquis de Courtanvaux, count of Tonnerre and duke of Doudeauville, 49, a distinguished chemist by the way, proposed to pay for a ship and a cruise to test it. The ship is a 130-ton 69-foot corvette named Aurore.

The ship departed from Le Havre to the North sea with a scientific staff and two chronometers aboard, the one presented to the Académie and a second, not tested yet but designed by Le Roy to be more advanced, which it effectively proved. We do not know the precise difference between these two. The first watch has cumulated a 4 minutes and 52 seconds delay during the 103 days of navigation, the second only 15 seconds - an amazing score, beyond any expectation. Less than three seconds a day for the first chronometer and a seventh of a second a day for the other, despite adverse weather conditions as it was looked for. The watches have been terribly shaken by a succession of storms in the North Sea, which makes the score even more meaningful.

Le Roy fully deserves the prize of the Académie, which, since 1722, has been mimicking the well-known Longitude Act. Experts concur to regard his work as a first-in-class achievement.

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IN RETROSPECT FROM TODAY

NOTE - on the aftermath

Aurore sails to the South around Spain for another trial, as convincing as the first. Then the chronometer is transferred and trialed aboard the frigate Enjouée with the same sort of score. Le Roy is awarded the prize of the Académie in 1769.

The best chronometers of Le Roy, named A and S, of Ferdinand Berthoud, the number 8, and several others from other makers will go on board the frigate Flore. She sails in 1771-72 from Brest to Gorée, Guadeloupe, Saint-Pierre & Miquelon near Newfoundland, Copenhagen and back to Brest. Le Roy's chronometers win the day once again and he is awarded the Académie's prize once more in 1773.

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CREDIT

Elisabeth Haussard (engraver) after Nicolas Ozanne (painter) - Flore - engraved in 1768 - © public domain