3. Nearly every one of the principal authors of antiquity has been explicitly mentioned, or criticised, or described, by later writers. Lists of their works have been given, with summaries of their contents; or they have been made the subjects of connected commentaries, by means of which the mass of the original work may be identified, and collated, with existing copies. Books of this secondary class are usually fraught with references to the entire circle of literature that was extant in the writer’s time. There are also extant several works containing the lives of ancient authors, with accurate lists of their works. These biographical pieces, while they have on one hand afforded a security against the production of spurious works, on the other hand have given occasion to such attempts; for if some treatise, known to have been written by a celebrated author, was believed to have perished, an opportunity was presented for composing one which should correspond with the description given of it. But such spurious works must always be deficient in positive evidence, nor will they fail to betray the imposition by some glaring inconsistencies in style, or in matter. The lives of statesmen and warriors often contain such allusions to the writers of the same age, as suffice to prove the time when they flourished. All the information we possess on this head is, in many instances, derived from allusions of this sort. 4. A copious fund of quotations is contained in some ancient treatises on particular subjects, in which all the authors who have handled the same topic are mentioned in the order of time. 5. Controversies, whether literary, political, or religious, have usually occasioned extensive quotations to be made from works of all classes; and, on the spur of an acrimonious disputation, many obscure facts have been adduced, which, by some circuitous connexion with other facts, have served to determine questions of literary history. 6. Among all the means for ascertaining the antiquity and genuineness of ancient books, none are more satisfactory or more complete than those afforded by the existence of early translations. Indeed, if such translations can be proved to have been made near to the time at which the author of the original work is believed to have lived, and if they correspond, in the main, with the existing text--and if they have descended to modern times through channels altogether independent of those which have conveyed the original work--and if, moreover, ancient translations of the same work, in _several languages_, are in existence, no kind of proof can be more perfect, or more trustworthy. In such cases every other evidence might safely be dispensed with. Ancient translations serve also the important purpose of furnishing a criterion by which to judge of the comparative merits of manuscripts, and by which also to determine questions of suspected interpolation.