Louis Prosper Gachard, a Belgian archivist, born in Paris, Oct. 12, 1800. He was a journeyman printer, joined the Belgian revolution of 1830, and was naturalized in Belgium in 1831. He was appointed archivist general, and commissioned to seek in the national and in foreign libraries for documents relating to Belgian history, and in 1834 became secretary of the historical commission. He has most dilisrently explored the archives of Simancas in Spain, and others at home and abroad, and has published a great number of works and documents relating to the history of Belgium. Among the works edited by him are many volumes of correspondence of William*the Silent, Charles V., Philip II., the duke of Alva, Margaret of Parma, etc, on the affairs of the Low Countries; official letters to the states general, and the acts of that body from 1576 to 1585; and Relations des troubles de Gand sous Charles V., par un anonyme, with 330 documents. In his work Jeanne la Folle (1869), he sets forth opinions opposed to those of Gustav Bergen-roth concerning the mother of Charles V.