paper, after leaving the wet felt, and before being taken on to the 2nd press felt, travels over the rolls _l′_. The 2nd press felt is necessary, because the paper is too tender to withstand, unsupported, the pressure of the rolls. [Illustration: FIG. 53.] The paper, after passing the 2nd press rolls, travels over the drying-cylinders M, the number of which varies somewhat. In the machine shown, there are in all eight cylinders. Sometimes as many as twelve are employed. Between the {158} 2nd press rolls and the cylinders, a passage S allows easy access to the other side of the machine. The paper generally passes alone over the first two, which are only slightly heated; afterwards it is led over the others by means of felts, as shown. The arrangements shown at R are for the purpose of stretching the felts. The cylinders are heated by means of steam, and are generally divided into two sets, between which is a pair of chilled-iron, highly-polished rolls N, called “smoothers,” the function of which is sufficiently explained by their name. They are also heated by means of steam. The cylinders are usually made of slightly decreasing diameter, in order to allow for the shrinking of the paper on drying. Messrs. G. & W. Bertram introduce into some of their machines one or two small drying cylinders, over which the 2nd press felt travels, the object being to drive off some of the moisture absorbed from the paper. This contrivance is said to give excellent results, and to ensure a considerable saving in felts. The arrangement is shown in Fig. 53. It is especially useful in machines running at a high speed, or in those having limited drying power. After leaving the cylinders, the paper should be quite dry; it is then led through the calenders, of which there are in some machines {159} as many as three sets, though only one is shown. These are similar to the smoothing-rolls, just described. Pressure is applied by the screws O′, or by levers and weights. The friction of the hot calenders on the dry paper develops a large quantity of electricity, which occasionally discharges itself in bright sparks. It is the practice in some mills to cool the paper before passing it through the calenders. This is effected by passing it over a copper cylinder, through which a stream of cold water runs.