The series of volumes known as the Encyclopaedia of Diderot and d’Alembert represents one of the most ambitious editorial undertakings during the Age of Enlightenment. First launched in autumn 1750, it took up the project initiated by several Parisian booksellers: to publish a French translation of the Cyclopaedia, or a Universal Dictionary of Arts and Sciences by Ephraim Chambers, a two-volume work printed in London in 1728. The Parisian Encyclopaedia was nonetheless more substantial: co-directed by writer and philosopher Denis Diderot and mathematician Jean Le Rond d’Alembert, it harnessed the talents of more than 140 contributors over a more than 20-year period running from 1751 to 1772. The final result comprises 27 volumes of text and 11 volumes of plates.
 

A true 18th century literary success, the Encyclopaedia aimed to gather all existing knowledge and to organise it in alphabetical order, with a cross-referencing system between various articles. The Encyclopaedia was intended for all cultivated readers with no distinction in terms of competence, thus bringing academic scholarship into the public realm. As recalled by its complete title – namely Encyclopaedia or Classified dictionary of sciences, arts and trades – one of its chief characteristics is the importance devoted to artisanal skills. Whereas printing of the Academy of Sciences’ Description des arts et métiers [Description of arts and trades] did not begin until 1760, the Encyclopaedia provided the first ever detailed description and illustration of technical procedures.

Unsurprisingly, horology is central to this work, with a total of 250 articles are devoted to this field, along with 70 plates – covering both timepieces themselves as well as their related mechanisms and tools. A number of articles are anonymous. The surveyor and member of the Academy of Sciences, Jean-Baptiste Le Roy, son of Julien Le Roy, is undoubtedly the most prolific author, having single-handedly written almost 90 texts, simply signed with a capital T. Geneva-based horologist Jean Romilly also contributed ten or so articles and was notably entrusted with commentary on some of the plates.
 

It is impossible to get a clear grasp of the logic behind the recruitment of these specialists. The selection of contributors for the horology articles was probably conducted via d’Alembert, himself an eminent member of the Academy of Sciences. It is highly plausible that Ferdinand Berthoud’s participation stemmed from his own contacts with the Academy of Sciences. Berthoud notably submitted a memoir on an equation-of-time clock to this institution in 1752, followed two years later by approval for a second equation-of-time clock. This meant that the “Equation (Horlogerie &c.)” article is one of those he signed as follows: “This article is by Mr Ferdinand Berthoud, horologist”. Two other articles “Fendre (Machine à)” [Gear-wheel slotting machine] and “Fusée (Machine à tailler les)” [Fusee-cutting machine] also bear his signature.
 

Historians also believe he authored the anonymous articles entitled “Pendule en tant qu’appliqué aux horloges (Horlogerie)” [The pendulum as applied to clocks] and “Répétition (Horlogerie)” [Repeating mechanisms in watchmaking]. Those named “HorlogER” [Horologist] and “HorlogerIE” [Horology], which form a whole, are not officially signed either, yet Berthoud’s authorship is in no doubt. The note concluding the “HorlogerIE” article indeed states that “I made a Preliminary Discourse in my Essay on Horology from this article that I initially composed for this Dictionary”.