The degree of smoothness or “finish” that can be given to the paper by the calenders, depends to a large extent upon the degree of moisture which it contains. As it leaves the last cylinder it is perfectly dry, that is to say, it contains only that amount of water which cellulose, from whatever source, always carries. This amount varies slightly with the nature of the cellulose, and with the plant from which it has been isolated, and also with the state of the atmosphere, it being greater on damp days. It would be impossible so to regulate the drying action of the cylinders that the requisite amount of water should always be left in the paper; it is therefore better to dry it as thoroughly as possible, and then to add the water, by artificial means, just before it passes through the calenders. This method, moreover, has the advantage of damping only the surface of the paper. Fig. 54 shows a damping arrangement as manufactured by Messrs. James Bertram & Son. The paper on leaving the last drying cylinder passes on to two copper cylinders _c_, filled with cold water. Steam passes through the pipe _a_, and issues through a number of fine holes in a pipe running at right angles to the direction in which the paper is travelling, and near to it. The steam condenses on the paper and on the surface of the cylinders, from which the paper absorbs it. The supply can be regulated by the cocks shown in the drawing. The troughs _d_ carry off any excess of condensed water. Amongst other methods proposed is one by Annandale; it {160} consists in breaking up jets of water into a very fine spray by means of a blast of air. The finished paper, after passing through the calenders, is wound on the reels P. The gearing by which the whole machine is driven is shown in Plate II. [Illustration: FIG. 54.] It sometimes happens that, owing to the increased tension due to the contraction of the paper in drying, the paper breaks. It is therefore necessary to alter the speed of some of the cylinders to compensate for this. A rough expedient which is largely adopted, consists in attaching, by means of a mixture of rosin and tallow, a piece of felt to one or other of the pulleys (Plate II.), and thus altering its speed.