The most voluminous work of the Philosophers is the "Encyclopaedia," a book of great importance in the history of the human mind. The conception of its originators was not a new one. The attempt to bring human knowledge into a system, and to set it forth in a series of folio volumes, had been made before. The endeavor is one which can never meet with complete success, yet which should sometimes be made in a philosophic spirit. The universe is too vast and too varied to be successfully classified and described by one man, or under the supervision of one editor. But the attempt may bring to light some relation of things hitherto unnoticed, and the task is one of practical utility. The great French "Encyclopaedia" may claim two immediate progenitors. The first is found in the works of Lord Bacon, where there is a "Description of a Natural and Experimental History, such as may serve for the foundation of a true philosophy," with a "Catalogue of particular histories by titles." The second is Chambers's Cyclopaedia, first published in 1727, a translation of which Diderot was engaged to edit by the publisher Le Breton. Diderot, who freely acknowledges his obligation to Bacon, makes light of that to Chambers, saying in his prospectus that the latter owed much to French sources, that his work is not the basis of the one proposed, that many of the articles have been rewritten, and almost all the others corrected and altered. There is no doubt that the whole plan of the "Encyclopaedia" was much enlarged by Denis Diderot himself.[Footnote: Bacon, iv. 251, 265. Morley, _Diderot_, i., 116. Diderot, _Oeuvres_, xiii. 6, 8. "If we come out successfully we shall be principally indebted to Chancellor Bacon, who laid out the plan of a universal dictionary of sciences and arts _at a time when there were, so to speak, neither sciences nor arts_."]