Those who have been long accustomed to inspect and examine ancient manuscripts acquire a certain tact in judging of the age of a book from the condition of the ink, its colour and composition, which cannot be explained to others, and for the exercise of which no rules can be laid down. But in cases where a fraud is suspected, this nice habit of the eye often detects at once the imposition. It is perhaps more practicable to give to a picture, than to a manuscript, the hue of antiquity by artificial means. CHAPTER VI. CHANGES INTRODUCED IN THE COURSE OF TIME IN THE FORMS OF LETTERS, AND IN THE GENERAL CHARACTER OF WRITING. An exact uniformity in the shapes of letters, and in the general appearance of writing, is hardly maintained for so long a period as fifty years in any language, especially if it be widely diffused. Within that space of time, the fashion of our own typography has undergone several changes, so perceptible as to afford a tolerably certain criterion of the date of books. No person, for example, who is familiar with books, would find it difficult, merely from the character of the type, to discriminate the age of works published at the several periods of 1775, 1800, 1825, and 1855. On similar grounds a knowledge of the successive changes introduced by caprice, accident, or a regard to convenience, in the ancient modes of writing, affords an almost certain means of determining the age of manuscripts. The knowledge requisite for the exercise of this discrimination is derived, in part, from incidental allusions to modes of writing which occur in some ancient authors; but principally from an extensive comparison of manuscripts themselves, and from a comparison of manuscripts with inscriptions upon marbles, brazen tablets, or coins. From these sources may be collected a sufficiently precise idea of the character or fashion of writing prevailing in each century, from the second, to the fifteenth, of the Christian era. The oldest Greek manuscripts that are extant differ little in the form of the letters, or the general appearance of the writing, from inscriptions belonging to the corresponding periods. They are written in capitals, called uncials, without division of words, and without marks of accentuation or punctuation. About the seventh century, the custom of affixing the accents and aspirates appears to have been introduced; at the same time a greater degree of precision was observed in the formation of the letters, and also in the directness and the parallelism of the lines. To these improvements was added a change in the form of those letters which most impeded the rapid movement of the pen.