# Marine Chronometer > Pierre Le Roy - 1766 > Canonical HTML: https://iconotheca.com/artworks/pierre-le-roy/le-roy-marine-chronometer-cnam/ > Published by Servola Systems GmbH. Last verified: 2026-09-18 ## Tombstone - **Artist:** Pierre Le Roy - **Date:** 1766 - **Medium:** Wood, steel, brass and glass; detent escapement, temperature-compensated bimetallic balance, isochronous balance spring - **Dimensions:** 35 x 25 x 25 cm (outer gimbal box) - **Object type:** Clocks and instruments - **Period:** French, eighteenth century - **Current location:** Musee des Arts et Metiers (Conservatoire national des arts et metiers), Paris - **Attribution:** accepted ## Summary A small brass, steel and wood marine timekeeper of 1766, built by the Parisian royal clockmaker Pierre Le Roy and tested at sea aboard the corvette Aurore in 1767. It carries, in one working object, the three mechanisms that every marine chronometer built afterward actually used: a detached detent escapement, a temperature-compensated balance and an isochronous balance spring. John Harrison solved the longitude problem first and more famously, but the trade that followed did not copy Harrison's H4; it copied this.Le Roy entered the machine, and a duplicate of it, for the Academie des Sciences' Meslay prize. The two Le Roy watches were the only entries actually produced for the 1767 trial; his rivals' machines were withdrawn or damaged before the ship sailed. Le Roy won the double prize in 1769, was outmanoeuvred in reputation by his rival Ferdinand Berthoud regardless, and died in 1785 without ever receiving the recognition or the money that Harrison had received from the British Parliament for less durable ideas.The object has been at the Conservatoire national des arts et metiers, in Paris, since before 1923, when the horologist and historian Rupert Gould examined it there and wrote what remains the most-cited English-language judgment on it: that the credit for designing the first modern chronometer belongs to Le Roy, and to Le Roy alone. ## Provenance Every link carries a grade. `documented` means a cited source supports it, `disputed` means the identification is argued but not established, `unknown` means we have no owner for that span and have not bridged it. - **1766** Pierre Le Roy `[documented]` (manufacture and presentation) Built by Le Roy in his workshop with lodgings in the royal galleries of the Louvre, where he held the post of horloger du roi. He presented the finished machine to Louis XV in 1766 and submitted it, with a duplicate of the same design, to the Academie des Sciences for the Meslay longitude prize. - **1767** Academie des Sciences, via the Marquis de Courtanvaux `[documented]` (sea trial) Tested aboard the corvette Aurore, a vessel purpose-built at Courtanvaux's own expense for the trial, on a roughly three-month coastal cruise from Le Havre via Calais, Dunkirk, Rotterdam, Brielle and Amsterdam and back to Le Havre, departing 14 May and returning by 28 August 1767. Le Roy's machine and its duplicate were the only timekeepers actually produced for the trial; entries by Romilly and Tavernier were withdrawn after Romilly's machine was accidentally damaged during a preliminary shore test. Courtanvaux's own report to the Academie records the first watch's error at 38 seconds over 46 days of steady comparison and the second, later-built watch's error at 7.5 seconds over the same period; a separate secondary tally elsewhere gives the first watch an error of 4 minutes 52 seconds over a 52-day outbound leg and 51 seconds on the return leg. Both figures are given here because the sources consulted do not agree, and this record does not resolve the discrepancy by picking one. - **1769** Pierre Le Roy `[documented]` (second sea trial and prize) Tested again aboard the frigate L'Enjouee on a roughly six-month voyage from Le Havre to Newfoundland, Cadiz and back to Brest. Results were of the same order as the first trial. The Academie awarded Le Roy its double Meslay prize for the timekeeper and the accompanying memoir, while noting in its report that one trial had shown a sudden acceleration of 11 to 12 seconds per day even on land, so that, in the Academie's own words, the desired degree of perfection had not yet been obtained. - **1771** Pierre Le Roy `[documented]` (third sea trial) Entered again, alongside a new competition for a second Academie prize, in the frigate La Flore against a weight-driven machine by Arsandeaux and a pendulum clock by Biesta. Le Roy again won, though less decisively than before; the ship struck Wilmington rock off Antigua during the voyage, breaking a thermometer on his first machine and putting it out of action as a timekeeper for the rest of the trial. - **1771** Pierre Le Roy, then unrecorded `[unknown]` (gap) Le Roy is recorded as considering his design essentially finished after 1771, beginning work on a further machine late in life of which no details survive, and dying in 1785. No source consulted documents how or when this specific object passed out of his hands and into what became the Conservatoire national des arts et metiers, founded in 1794 in the nationalised buildings of the former Priory of Saint-Martin-des-Champs. The museum's early holdings absorbed royal and Academie instrument collections in the Revolutionary period, which is the plausible route, but this record has found no accession document naming this object and does not assert the route as fact. - **-1923** Conservatoire national des arts et metiers `[documented]` (confirmed holding) Rupert Gould examined the object at the Conservatoire des Arts et Metiers in the early 1920s for his 1923 monograph, describing it there as 'the wonderful machine preserved in the Conservatoire des Arts et Metiers.' This is the earliest source consulted that places the object in the museum by name, and it had evidently been there for some time already. - **1923-present** Musee des Arts et Metiers (Conservatoire national des arts et metiers), Paris `[documented]` (continuous holding) Held continuously as inventory CnAM 01395-0000-, on the museum's own online collections database and mirrored on Wikidata. It is displayed among the museum's horology holdings alongside instruments by Antide Janvier and Ferdinand Berthoud. ## Open questions - How and when did this specific object pass from Pierre Le Roy's possession into what became the Conservatoire national des arts et metiers? No source consulted documents an accession event; the museum was founded in 1794 from nationalised buildings and collections, which is a plausible but unconfirmed route. - Which of the two figures for the 1767 Aurore trial's accuracy is correct: the 38 seconds and 7.5 seconds over 46 days translated by Gould directly from the Academie's report, or the 4 minutes 52 seconds and 51 seconds over 52 and an unspecified return-leg figure found in later secondary accounts? The two do not obviously describe the same measurement window and this record has not been able to reconcile them. - Does CnAM 1395 correspond to Le Roy's first watch (the one damaged en route to Le Havre and later disabled again off Antigua) or his second, more accurate watch, or is it a later, separate machine altogether? The museum's own record does not specify, and Le Roy is documented as having built more than two examples across his career, including a smaller 'petite ronde' variant that performed poorly and is explicitly not this object. - Did Pierre Le Roy die on 25 or 26 August 1785? Gould's 1923 account, closest in time among the sources consulted, gives the 25th; other secondary sources give the 26th. - What happened to the unfinished machine Le Roy is recorded as having begun in his final years? No source consulted records whether it was completed, by whom, or where it might now be, if it survives at all. - Is there a surviving contemporary portrait of Pierre Le Roy? Gould, writing in 1923 as the leading English-language authority on the subject, stated he could not find one and suspected none existed. A file on Wikimedia Commons uploaded in 2009 and labelled as an eighteenth-century portrait of Le Roy, sourced only to an unspecified 'Haute Horlogerie archive,' has not been independently verified against Gould's judgment and is not used as an image in this record for that reason. ## Sources - [1] Rupert T. Gould, The Marine Chronometer: Its History and Development (London: J. D. Potter, 1923), chapter VI, 'Le Roy and Berthoud'. - [2] Wikipedia, 'Pierre Le Roy'. Tertiary source; used for orientation and cross-checked against Gould and the corvette Aurore article, flagged for replacement with a scholarly biography where one becomes available. - [3] Wikipedia, 'French corvette Aurore (1767)'. Tertiary source giving the Aurore's construction, funding by Courtanvaux, and a route and error tally for the 1767 trial that differs from the figures translated by Gould from the Academie's own report; both are given in this record. - [4] Corvette Aurore trial report, as translated by Rupert Gould from the Marquis de Courtanvaux's account to the Academie des Sciences, in The Marine Chronometer (1923), pp. 91-92. - [5] Academie des Sciences, report on the 1769 sea trials, as translated by Rupert Gould in The Marine Chronometer (1923), p. 92. - [6] Wikidata, 'Le Roy Marine clock - CnAM 1395' (Q86837647), mirroring the Conservatoire national des arts et metiers' own collections record for inventory 01395-0000-. - [7] Wikimedia Commons, extended metadata for File:Pierre Le Roy chronometer full view 1766.jpg, confirming licence CC BY-SA 3.0 and photographer PHGCOM, and Category:Le Roy Marine clock - CnAM 1395, confirming the four files in that category depict the same catalogued object. - [8] The Ministry of Horological Affairs (Carlos Torres), 'The Other Side of the Channel'. An independent horological-history blog, not a peer-reviewed source, used here only for its framing of the popular Harrison-centred narrative against the technical-historical case for Le Roy; flagged for replacement with a peer-reviewed article if one is located. - [9] Smithsonian National Air and Space Museum and National Museum of American History, 'Innovations in France', Time and Navigation. - [10] P. de Vanssay de Blavous, review of works by Paul Ditisheim, Roger Lallier, L. Reverchon and Commandant Vivielle on Pierre Le Roy, The International Hydrographic Review, vol. XX (1943). Cited here only for its bibliographic existence, as evidence that French hydrographic and horological scholarship continued to treat Le Roy as a subject of serious study into the twentieth century; the article's own text could not be extracted from the scanned PDF and no claim in this record is attributed to its content. - [11] Wikipedia, 'Julien Le Roy'. Tertiary source, used only for Julien Le Roy's dates and royal appointment, cross-checked against Gould. --- Images on this record are public domain or CC0 and are hosted by us. No image on this site is generated or simulated. If you quote this record, quote the provenance grades with it.