Nothing should be neglected; nothing is useless to whoever wishes thoroughly to study a subject. An astronomer, who desires to study the motions peculiar to certain stars, requires to consult all the old books of astronomy, and even of astrology, which appear the most replete with error. A chemist, a man who is engaged in the industrial arts, may still consult with profit certain works on alchemy, and even on magic. A legislator, a jurisconsult, needs sometimes to be acquainted with the laws, the ordinances, which derive their origin from the most barbarous ages; but it is particularly for the biographer, for the historian, that it is necessary to prepare the largest field of inquiry, to amass the greatest quantity of materials. This is not only true as regards past times, but we ought to prepare the materials for future students. Historical facts which appear the least important, the most insignificant anecdotes, registered in a pamphlet, mentioned in a placard or in a song, nay be connected at a later period in an unforeseen manner with events which acquire great importance, or with men who are distinguished in history by their genius, by their sudden elevation, or even by their crimes. We are not born celebrated--men become so; and when we desire to trace the history of those who have attained it, the inquirer is often obliged to pursue his researches in their most humble beginnings. Who would have imagined that the obscure author of a small pamphlet, "Le Souper de Beaucaire," would subsequently become the Emperor Napoleon? and that to write fully the life of the execrable Marat, one ought to have the very insignificant essays on physics that he published before the Revolution? Nothing is too unimportant for whoever wishes thoroughly to study the literary or scientific history of a country, or for one who undertakes to trace the intellectual progress of eminent minds, or to inform himself in detail of the changes which have taken place in the institutions and in the manners of a nation. Without speaking of the commentaries or considerable additions which have been introduced in the various reprints of an author, the successive editions of the same work which appear to resemble each other the most, are often distinguished from each other by peculiarities worthy of much attention. It has been well said, that a public library should contain all those works which are too costly, too voluminous, or of _too little value_ in the common estimation to be found elsewhere, down even to the smallest tracts. An old almanac, or a forgotten street-ballad, has sometimes enabled the historian to verify or correct some important point which would otherwise have remained in dispute.