3247. Books are distinguished according to the number of pages in a sheet of the paper on which they are printed; as, two leaves,4 pages, folio; four leaves, 8 pages, quarto, or 4 to; eight leaves, 16 pages, octavo, or 8vo; twelve leaves, 24 pages twelves, duodecimo, or 12mo.; sixteen leaves, 32 pages, sixteens, or 16 mo.; eighteen leaves, 36 pages, octo-decimo, eighteens, or 18mo. The size of a book is determined by the size or designation of a sheet of the paper on which it is printed; as foolscap 4to., or 8vo.; post 8vo.; demy 8vo.; royal 8vo., etc.

3248. The letters A, B, C, D, etc. and the letters and figures, A 2, A 3, A 4, etc, at the bottoms of the first, third, fifth, seventh, etc., pages of printed sheets, are marks for directing the printer, bookseller, and bookbinder in collecting, collating, folding and placing the sheets in proper order. These marks are usually termed signatures.

3249. When the page of a book it divided into two or more parts by a line or lines, or blank spaces, running from the top to the bottom, each division is called a column. This work is printed in columns.

3250. Vignette is a French term, designating the ornamental engraving, without a border, which is sometimes placed in the title-page of a book, at the head or termination of a chapter, etc.

3251. Xylography is the art of engraving upon wood; etching, mezzo-iinto, and aquatinta, are varieties of the art of engraving upon copper. Until within these few years, copper and wood were the substances employed by engravers for book-illustrations. For certain purposes, wood (box-wood) continues in the highest repute; but copper has been in a great measure superseded by steel, where a large number of impressions is required.

3252. Electrography is a newly-discovered electrical process, by which one copper plate may he expeditiously produced, in fac simile from another.

3253. Glyphography is a somewhat similar process, by which through the action of the voltaic battery, plates may be obtained from drawings, affording impressions ad libitum.

3254. Lithography is the art of taking impressions from drawings or writings made on prepared and highly-polished calcareous stone. Zincography is an adaptation of the same principle to plates of Zinc. All these processes are now extensively employed in the illustrations of books for various purposes. (See 1850 and 3360.)