Having underestimated the complexity of
publishing the vast Encyclopédie Méthodique, Charles-Joseph Pancoucke found it necessary to issue a second lengthy prospectus in order to explain to subscribers the complex road ahead in completing the project. This 84-page prospectus he issued as part of the third volume on Mathematiques published in 1789. In 2021 I was fortunate to obtain a copy of this prospectus separately bound in old boards. Since the original prospectus from 1781 exists in only four known copies, this second prospectus was the only one that I had a chance of acquiring.
Published without a proper title page, the 1789 prospectus begins with a "Table des objets," followed by a preamble signed by De Maissemy, dated 27 February 1789, which states certain modifications of the conditions of the subscription, including a "Supplément de Souscriptions, l'Encyclopédie devant avoir plus du double de volumes qu'on n'en avoit." This is followed by a long presentation by Sieur Panckoucke, explaining the state of the production, the legal and financial problems, and announcing the translations in progress into Spanish. Subsequently we find a "Letter from Mr. Panckoucke (2 pages) written to the Authors of the Encyclopaedia" (dated November 1788), followed by another text by the same author, "Sur les prétendus Bénéfices actuels de cet Ouvrage'"(3 pages), and the correspondence between
Panckoucke and M. le Comte d'Hulft (5 pages), followed by the"'Etat des nouveaux Volumes du Discours & de Planches qui publiront en 1789" (State of the new volumes of the Discourse & of the Plates which will appear in 1789) and other information such as the "Noms des Auteurs de l'Encyclopédie actuelle"(1 p.).
Pancoucke devoted the second half to the prospectus to a "Tableau et apperçu du nombre devolumes de Discours & de Planches que doit avoir l'Encyclopédie par Ordre de Matières , qu'on a jugé à propos de faire & d'ajouter pour compléter et perfectionner cet Ouvrage" (56 p.) Here he provided detailed information on the individual subject volumes, with details of the main contributors, and a rough outline of the contents covered.