If the grain runs parallel to the shelf-back no harm results, as the paper is free to expand toward the side margin, but if the grain is at right angles it usually makes a cockle in the binding because the moistened edges of the leaves expand while the dry portion beyond where the moisture penetrates retains its shape and resists the elongation of the wet edges. Consequently the expansion of the fibers expresses itself by cockling. REGISTER.--In all printing, when close register is necessary, the danger of poor register from the expansion of paper is minimized when the dimension across the grain is the shorter. Lithographers invariably prefer to have the grain run the long way of the sheet on this account. Moreover, they rack the paper before printing in order to get it thoroughly seasoned. To protect it from atmospheric changes that may occur during the printing process, they use slip-sheets of considerably larger dimensions, so that there is a generous margin of slip-sheet around each printed sheet, which helps to exclude the air from the edges of the printed paper. MOISTURE IN PAPER.--It is true that some papers are more prone to expand than others, especially if they have been run too dry on the machine. Paper is not naturally bone-dry. Under average weather conditions, it contains six or seven per cent of moisture.[D] When in the making it is turned off far below its normal moistness, it seeks to obtain this moisture from the air at the first opportunity, and in acquiring it expansion takes place. Unless the expansion pervades the entire sheet, wavy edges will result. Similarly when the air becomes dry exposed edges of paper give off some moisture and shrink accordingly leaving a boggy center to the sheets. [D] See Herzberg table, page 64. SEASONING.--This process of acquiring normal moisture is usually called “seasoning.” As paper is probably never turned off at its full normal moisture, it is most desirable that it should be allowed time to season. It is not unusual to have people speak of new paper being too “green.” This may not have been an uncommon condition of hand-made papers which were dried entirely naturally, but, so far as machine-dried paper is concerned, I doubt if it is ever too green, though it is frequently made too dry.