DIDEROT (Denis), ALEMBERT (Jean Le Rond d’) Geneva, Neuchâtel, Jean-Léonard Pellet, published by the Typographical Society, 1778–1779. Encyclopédie, or Reasoned Dictionary of the Sciences, Arts and Trades. 39 vols. in-4, marbled calfskin, ribbed spine decorated with gilt motifs, red title labels and anthracite volume numbers (contemporary binding). First edition in quarto format of this monument to Western thought. Two portraits as frontispieces and several folded plates within the text volumes. The three volumes of plates contain 444 leaves, 99 of which are folded, some comprising several ‘plates’. A few tears to the bindings, very rare defects on the plates (mainly marginal), but a fine set nonetheless. Provenance: Heraldic bookplate bearing the motto ‘Spero’.