As no air-pump can by any means make a perfect vacuum, so neither can any artist entirely exclude the conventional, the local, the perishable from his book, or write a book of pure thought, that shall be as efficient, in all respects, to a remote posterity, as to contemporaries, or rather to the second age. Each age, it is found, must write its owns books; or rather, each generation for the next succeeding. The books of an older period will not fit this.