Some of the principal imperfections which are more easily observed by the man of practical knowledge in the art of printing are the following: viz. imperfect, wrong-founted, and inverted letters, particularly the lower-case n, o, s, and u, as well as p, d, b, and q; awkward and irregular spacing; uneven pages or columns; a false disposition of the reference marks; crookedness in words and lines; bad making-up of matter; erroneous indention, &c. These minutiæ, which are rather imperfections of workmanship than literal errors, are apt to be overlooked and neglected by mere literary readers. A person of a thoroughly cultivated typographical taste, a quick eye, and a ready mind, though not a compositor, may doubtless be competent to detect those minor deviations from exact workmanship in a proof which the inexperienced and the careless are apt to overlook. But, without these qualifications, no person can be safely intrusted to read a sheet for press, and the labours of the printer are liable to go forth into the world in a manner that will reflect discredit on the employed and give offence to the employer. No form, therefore, ought to be put to press until it has been read and revised by an _experienced_ reader. A thorough proof-reader, in addition to a general and practical acquaintance with typography, should understand clearly the grammar and idiomatic structure of his mother-tongue, and have, as it were, an encyclopedic knowledge of the names, times, and productions of its writers, as well as an entire familiarity with the Bible especially, and with Shakspeare. He should be, in fact, a living orthographical, biographical, bibliographical, geographical, historical, and scientific dictionary, with some smattering of Hebrew, Greek, Latin, French, Spanish, Italian, and German. Yet all these accomplishments are valueless unless he also possess a keen and quick eye, that, like a hound, can detect an error almost by scent. There are eyes of this sort, that with a cursory glance will catch a solitary error in a page. The world is little aware how greatly many authors are indebted to a competent proof-reader for not only reforming their spelling and punctuation, but for valuable suggestions in regard to style, language, and grammar,—thus rectifying faults which would have rendered their works fair game for the critic. Although no corrector of the press can strictly be required to do otherwise than to _follow his copy_,—that is, faithfully to adhere to the original, with all its defects,—yet every one must perceive that he performs a friendly and perhaps a charitable service, by pointing out, in proper time, imperfections and mistakes which have escaped the observation of a quick or voluminous writer. With the spirit, the opinions, the whims of an author, no corrector of the press has any business to interfere. In reprints of old and standard works, no license of alteration ought to be granted to either correctors or editors.