The Great Encyclopedia for the Educated Classes by Joseph Meyer (1796-1856).
Ultimately numbering 52 volumes, Das Grosse Konversations-Lexikon für die gebildeten Stände was the most comprehensive completed German encyclopedia of the 19th century, also called "der Wunder-Meyer" (The marvellous Meyer). The complete set was reprinted 1858-59. ... The 9th edition, now from Mannheim, entitled Meyers Enzyklopädisches Lexikon in 25 Bänden (in 25 volumes), appeared in 1971-79. Just like the very first, this final Mannheim edition was the most comprehensive German encyclopaedia of the century.