If a portion were pressed too hard it would contain less moisture as it reached the driers and become dry before adjacent sections. If the paper were calendered, the moister parts would take on a smoother surface than the drier parts. Another feature to be closely watched on particular papers is to eliminate, as far as possible, the impress of the weave of the wire cloth, which is left in the under side of the web. This can be accomplished to so fine a degree, by a skilful man, that the difference between the two sides of the paper is scarcely discernible. The fineness of weave of the one cloth also is an important bearing in securing an even sided sheet. Thus we see that it is well-nigh impossible to reduce the making of paper to an exact science, and a reasonable variation must be expected, both in weight and finish. The successful management of a paper-machine depends, from start to finish, on careful, experienced judgment and alert attention. If the beater-man dilutes one batch of stuff more than another, the variation will show the minute the altered stuff appears on the machine, and only an immediate readjustment at the wet end can avoid considerable variation in the product. Then, from end to end, the long machine must be watched carefully, so that the pressing, drying and calendering may all be kept uniform. A bungler should find no place in the machine-room, but it is desirable that consumers have sufficient appreciation of human limitations, as applied to paper-making, to admit proper allowances for normal variations. CYLINDER MACHINE.--The cylinder machine, invented by John Dickinson about ten years after the Fourdrinier, is much the same as the wet machine described in Chapter II, with the addition of press rolls, driers and calenders. The single-cylinder machine is used for making light-weight tissues and other thin papers. Cylinder vats can also be arranged in series, as on board machines, so that the webs formed on each cylinder can be combined. This is accomplished by an arrangement of felts which run tangent to the cylinders, picking off the formed paper automatically from each successive mold. The felt runs between squeeze rolls, so that the various plies of paper are pressed together, forming a single thickness. Machines of this type can make very thick sheets, and are used for making bristol boards, blanks, boxboard, strawboard, etc. The number and arrangement of driers on any machine depends on the product to be derived. Fast-running machines, such as the large news mills are equipped with, have necessarily a large number of driers, as they turn off fifty tons or so a day and require a great drying capacity. Slow running machines, such as are used in fine writing-paper mills, need a much smaller number, as the average fine writing-paper machine produces little over three or four tons a day. [Illustration: CYLINDER VATS, MADE BY THE PUSEY & JONES CO.