early 1761. He filed an addendum on 28 February 1761. The clock was displayed in April 1763 at the Royal Academy of Sciences.- In 1754, the French Academy of Sciences approved a watch and equation clock by Ferdinand Berthoud.- Ferdinand Berthoud devoted himself to research and passing on his knowledge through his publications. This twofold aim earned him rapid acceptance in the scientific circles of his day. Several articles in the Encyclopédie méthodique, published in 1751–1772, under the direction of Diderot (1713–1784) and d'Alembert (1717–1783), were entrusted to him. In 1759, Berthoud published a successful popular treatise, L'Art de conduire et de régler les pendules et les montres. À l'usage de ceux qui n'ont aucune connaissance d'horlogerie1.6 In 1763, his lengthy treatise L'Essai sur l'horlogerie ; dans lequel on traite de cet Art relativement à l'usage civil, à l'Astronomie et à la Navigation was also well-received. This popular work was very successful, translated into several languages, and republished several times in the eighteenth and nineteenth centuries. 1763 marked a turning point in Berthoud's career, which from then on focused on the progress of maritime navigation. Once again, the French Academy of Sciences was to be both a witness and a support: in that year, the watchmaker had two envelopes opened that had been filed in 1760 and 1761. These describe the Sea Clock number 17. On 29 August of the same year, Ferdinand Berthoud filed another envelope entitled Construction d'une montre marine… His work was characterised by regular projects accompanied by detailed requests. For instance, he proposed the construction of two sea watches on 7 May 1766. These were Numbers 6 and 8 , now preserved at the French Museum of Arts and Trades. Following successful experiments with them, Ferdinand Berthoud received the title of "Horologist-Mechanic by appointment to the King and the Navy for the inspection of the construction of sea clocks" on 1 August 1770. In 1773, Ferdinand Berthoud published his Traité des horloges marines contenant la théorie, la construction, la main-d'œuvre de ces machines et la manière de les éprouver, pour parvenir par leur moyen, à la rectification des cartes marines et à la détermination des longitudes en mer. This treatise was a first, detailing all the parts required for building a sea clock. It helped seal the reputation of Berthoud's work, in particular with respect to his competitors in longitude at sea research, such as Harrison