Berthoud was entrusted with the task of writing a number of reference articles on watchmaking for the Encyclopédie méthodique1, published between 1751 and 1772 under the direction of the writer and philosopher Diderot (1713–1784) and the mathematician and philosopher d'Alembert (1717–1783). Ferdinand Berthoud published his first specialist work in 1759, L'Art de conduire et de régler les pendules et les montres, à l'usage de ceux qui n'ont aucune connaissance d'horlogerie1 [1]. Several other written works followed, detailed in the "Works" section. In 1763, Ferdinand Berthoud was appointed by the King to inspect the H4 sea watch made by John Harrison (1693–1776) in London, in the company of mathematician Charles-Etienne Camus (1699–1768), a member of the French Royal Academy of Sciences, and astronomer Joseph-Jérôme Lefrancois de La Lande (1732–1807). It was a disappointing trip for Berthoud: Harrison only showed him his H1, H2, and H3 watches (in exchange for a payment of £500), categorically refusing to show him the legendary H4, the most advanced of them all. Although Berthoud was not able to see Harrison's famous H4 in London, his trip did offer him a way into English scientific circles, due to the importance of his works and publications in the field of watchmaking. This resulted in him being elected on 16 February 1764 as an "associate foreign member" of the Royal Society in London. In 1764, by order of the King, the French Academy instructed two of its members, Duhamel de Monceau and Jean-Baptiste Chappe d'Auteroche, to test Ferdinand Berthoud's number 3 sea watch at sea. Berthoud reported that he wore the watch personally in Brest and was present for the tests. The trials took place on the frigate L'Hirondelle. In 1765, Ferdinand Berthoud undertook a second trip to London to meet Harrison through the offices of Count Heinrich von Brühl (1700–1763), Minister of Saxony. Harrison once again refused to present his creations to Berthoud, knowing that he was fully capable of using them to benefit the French Navy. It was the English horologist Thomas Mudge (1715–1795), famous for his development of the first detached lever escapement and a member of the Board of Longitude, who described the working principle of the H4 watch to Berthoud, without him being able to see it for himself (Harrison demanded a payment of £4,000 for a description of his watch, an exorbitant and dissuasive amount). On 7 May 1766, Ferdinand Berthoud sent a