--4^o in size. If the once folded sheet be folded again across the other way we get a gathering with four leaves, or eight pages, called a quarto. The chain lines are horizontal, and the watermark in the middle of the back of pp. 4 and 5; there are two foldings and two tops of leaves to be cut. --8^o. If the quarto be again folded we get a gathering of eight leaves, or 16 pp., called an octavo, which is the commonest size for English books. In an octavo there are three foldings, the chain lines are perpendicular, the watermark is quartered at the tops of pp. 3, 4, 11 and 12, and there are two tops and two fronts to be cut. The further foldings of 16^o, 32^o, and 64^o are the same operations carried further, but although such sizes do exist they are so uncommon that a further description of them is not necessary. --12^o. In the case of a duodecimo a different initial folding is followed. The original sheet instead of being folded once across the middle, as in the case of a folio, is now folded into three equal divisions. The parallelogram thus formed is folded across its shorter diameter, and this again along its longer diameter. There is now a gathering of twelve leaves, or 24 pp., with four foldings, the chain marks perpendicular, the watermark halved at the tops of pp. 3 and 9, and there are two tops and four fronts to be cut. It is the commonest size of the smaller French books. [Illustration: FIG. 64.--8^o.] [Illustration: FIG. 65.--12^o.] As to sizes, folios run from the great Atlas of Charles II., measuring five feet nine inches and a half by three feet two inches and a half, and requiring eight skins of morocco for its binding, to the tiny _Galileo a Madame Cristina de Lorena_, 1615, “imprimé en 1897,” measuring one half by one quarter of an inch. A folio cannot be recognised by its shape. The sizes of quartos and octavos are also very varied, but, roughly speaking, they can be recognised by their shapes, especially in the case of modern books. A quarto is generally squarish in outline, nearly as broad as it is long; an octavo is an elongated rectangle, its breadth considerably less than its length. A duodecimo is always much longer than its breadth. As curiosities, books have been made in many forms, circular, heart-shaped, octagonal, flower or animal forms, but they are of small importance, and have been chiefly made as Christmas cards, valentines, and such ephemeral publications. The rules as to quiring of books printed on paper do not apply to books printed on vellum. Such books are always folios, and they are generally quired in gatherings of ten leaves, following the fashion used in the ancient manuscripts, but, of course, they can equally well be gathered together in any even number that may be preferred. There is no rule.