The energies of the _Philosophes_ were given a centre and a rallying-point by the great undertaking of the _Encyclopaedia_, the publication of which covered a period of thirty years (1751-80). The object of this colossal work, which contained a survey of human activity in all its branches--political, scientific, artistic, philosophical, commercial--was to record in a permanent and concentrated form the advance of civilization. A multitude of writers contributed to it, of varying merit and of various opinions, but all animated by the new belief in reason and humanity. The ponderous volumes are not great literature; their importance lies in the place which they fill in the progress of thought, and in their immense influence in the propagation of the new spirit. In spite of its bulk the book was extremely successful; edition after edition was printed; the desire to know and to think began to permeate through all the grades of society. Nor was it only in France that these effects were visible; the prestige of French literature and French manners carried the teaching of the _Philosophes_ all over Europe; great princes and ministers--Frederick in Prussia, Catherine in Russia, Pombal in Portugal--eagerly joined the swelling current; enlightenment was abroad in the world.