The principle of the Stanhope press has been followed out by several subsequent inventors, and improvements of mechanical detail introduced, tending to the economy of time and labour, and to pre cision of workmanship. In the Ruthven press, the form of types remains stationary, and the plattin is removed to permit the types to be inked ; and in this, as well as the Columbian, the pressure is produced by a combination of levers alone, without the use of any portion of a screw or inclined plane.
The press for copper-plate printing consists of two cylinders, or rollers, of wood, supported in a strong wooden frame, and moveable about their axes, one placed just above and another just below the level of the table upon which the plate to be printed is laid. The upper roller is turned round by the arms of a cross fixed to its axis. The copper-plate being inked, the paper on which the impression is to bo taken, and two or three folds of soft material, as blanketing, are placed.upon it. The plate so prepared is moved along the table to the juncture of the two rollers, and the upper roller being turned by the arms of the cross, the plate, with its furniture, is passed through the press. The rollers may be placed nearer to or farther from each other, according to the amount of pressure requisite for making a good impression, that is, according to the depth of the engraving and the degree of blackness which the impression is required to have. With slight modification the same form is used for lithographic printing, to which steam-power has been recently applied very effectively.
Printing-Machine. —The printing-press, though much improved during the hat half-century by the ingenuity of Lord Stanhope and others, is quite inadequate to a rate of production equal to the present demand. The attention of practical men was consequently directed to some more rapid means of production, and as early as 1790, even before the Stanhope-press was generally known, Mr. W. Nicholson had letters-patent for a machine similar in many respects to those which have now come into use. Subsequently Mr. Ktinig, a German, con ceived nearly the same idea, and meeting with the encouragement in this country which he failed to obtain on the Continent, constructed a printing-machine, and on the 28th of November, 1314, the readers of the Tunes' were informed that they were then for the first time reading a newspaper printed by machinery driven by steam-power. This printing-machine, though highly ingenious, was very complicated, and the machine of Konig was soon superseded by that of Messrs. Applegath and Cowper, the novel features of which were accuracy in the register, the method of inking the types, and great simplicity in hitherto very complicated parts. Printing-machines may be distin
guished into single and double ; the single being that in which only one side of the sheet of paper is printed, the double that in which hoth sides are printed before the sheet leaves the machine. The former is used for newspapers and that kind of printing in which it is not neces sary for the two sides of the sheet to " register," that is, for the print ing on one side to be exactly at the back of the other ; the latter for books, in which it is essential that the printing on one page should correspond with the printing on the other when the sheets are folded. This important object of the register is effected by causing the parts to move at precisely the same speed. This being the principle of the register, its success will depend on great accuracy of workmanship in the mechanical parts. The accompanying representation of the printing 'machine will furnish a correct notion of the several parts, and of the way in which motion is communicated to them. A sheet of paper is taken from the pile to be printed (as represented at the left-hand side of the drawing), and put into the machine by one attendant, and taken out printed on both sides by the other attendant; whose hand is shown under the cylinders. The accompanying sketch will show the principle of the printing-machine.
The sheet of paper taken from the table A is laid on the feeder B, which consists of girths of linen, tightly stretched by being passed round two cylinders. By the motion of this feeder the sheet is placed between the two systems of tapes which lie on the cylinder o these tapes, of which one set is represented by the dotted line, and the other by the thin line, lie two and two over each other on the cylinders and small rollers a, b, c, d, e, f, g, i. The sheet of paper grasped between them is kept clean at the places in which it is in contact with them, and by the motion of the various parts is conducted under the first printing-cylinder at, and receives an impression from the types at c; thence by means of the cylinders I, K, to the second printing-cylinder I., where it receives an impression on the other side from the types at D. Thus printed on both sides, it is taken out at e by the attendant. The cylinders i and K are simply for the purpose of conveying the sheet steadily and smoothly from one printing-cylinder to the other. The sheet will be seen to be reversed in its progress from one set of types to the other, descending the left side of the first and the right side of the second printing-cylinder.