ing-offices, there are four tables or boards, at which are placed boys, called layers-on; each table has a heap of damped but unprinted sheets of paper; and it is the duty of the boys to lay these sheets, one by one,

on a kind of travelling belt or apron.

Each sheet is carried over a revolving cylinder, then over several rollers, and then under a second cylinder, by which it is pressed against the inked-type; the sheets, confined

Fig. 6.

6

at the edges between tapes, travel onward after being thus printed, and arrive at certain parts of the machine where other boys, called takers-off, receive them. The type, arranged in form,' and presenting a surface equal to that of one side of the sheet, has a traversing motion to and fro; it passes under a series of inking-rollers which ink all the types in a beautifully-equable manner; and it then passes successively under the cylinders around which the paper is wound. Newspapers are generally printed at two different times, one side in one machine, and the other side afterwards at another machine; this often enables the editors to introduce more recent news, in the interval between the two printings. In bookprinting, however, both sides are printed before the sheet leaves the machine; and it is thus managed:The two forms or sets of type, one for each side of the sheet, are placed on a horizontal carriage a certain distance apart; and each form has a distinct set of inking-rollers, and a distinct printing-cylinder. The ink is contained in a kind of trough, into which a metal roller, called the ductor, dips; the ductor becomes coated with ink; a vibrating-roller touches the ductor, takes off a little ink, and deposits it on the inking-table; three or four distributing-rollers spread the ink equally over the table; and the table, then travelling onwards, imparts a thin stratum of ink to three or four inkingrollers, under which it passes. The two impressioncylinders then revolve; the two forms of type travel to and fro; and the various inking-rollers receive their supply. The sheet of paper, wrapping tightly around one cylinder, is rolled over one form of type, and receives one impression: it then winds upon the other cylinder, rolls over the other form of type, and receives a second impression; and it thus travels on, printed on both sides, to a spot where the taker-off receives it. The machines may vary in complexity: they may print one side only, or both; they may print one, two, or four copies at once; but the essential parts of the mechanism are alike in all. The inking-apparatus supplies and regulates itself; the form obtains its quota of ink just at the proper time; and the cylinder brings the paper in contact with the

inked type exactly at the proper instant and in the proper spot. The whole of the operations are automatic, or self-acting, except the feeding of the machine with blank sheets of paper.

11. In the later and still more powerful vertical machine, such as is employed in printing the "Times and the "Illustrated News," the nature of the operation differs in many remarkable particulars. The heart or centre of the apparatus is a vertical cylinder or drum, more than five feet in diameter. This drum is to receive, not the paper, but the type and the inking-tables. Every column of type occupies a flat, narrow, upright space on the surface of the drum; and as many of these spaces are placed side by side (like the successive sides of a polygon) as there are to be columns of type. Every page of type, thus arranged, is printed from eight times during one revolution of the drum; for all the four pages, forming one surface of a sheet of the "Times," occupy together only one-eighth of the circumference of the drum-there is required, therefore, an eight-fold arrangement of inking-apparatus. There is a vertical reservoir of ink, from which a revolving ductor receives a continuous supply; there is an inking-table fixed to the drum, which, once in every revolution, receives a supply from the ductor; there are eight inking-rollers, placed equidistant around, but detached from the drum, and receiving in turn a supply of ink from the inkingtable; and there are eight impression-cylinders, each bringing its own sheet of paper to be printed. Nothing can be more beautifully exact than the order in which these several parts come into action: their movements are timed with rigorous accuracy. During one revolution of the large drum, its inking-table passes under eight inking-rollers, which impart eight inkings to the type; and a process of printing takes place between every two of these inkings. The movements of the sheets of paper are wholly distinct from all this, and are very remarkable. There are eight feeding-boards, each containing a pile of paper, and each attended by a boy, the layer-on. Each boy pushes a sheet of paper off the heap it is caught between two rollers, carried

downwards, and then sideways towards the drum; it is there seized by a cylinder, which presses it against the inked type, liberating it again immediately after the printing. Eight distinct sets of feeding-apparatus of this kind supply eight sheets of paper during each revolution of the drum; so that by the time this revolution is completed, there will have been eight copies of the "Times" printed on one side. The impression cylinders are about a foot in diameter, and are covered with cloth, to form a soft bed for the paper. It is evident that there are eight repetitions of the same process, all occurring during one revolution of the drum ; eight layers-on, eight feeding-tables, eight sets of apparatus to convey the paper to the drum, eight impression-cylinders, eight sets of inking-rollers, and eight takers-off to receive the printed sheets. The drum revolves twice in five seconds, and there are therefore printed sixteen sheets in five seconds.

12. Such is the general arrangement of this wonderful machine. Without any essential alteration to the central drum, there might be a greater or lesser workingpower, by increasing or diminishing the repetition of the other parts of the apparatus. The "Illustrated News" machine has four impression-cylinders, and four sets of apparatus for supplying ink and paper: consequently it produces only half as much work as the Times" machine. If, on the other hand, there were a duplication of the type-forms on the drum, the "Times" machine could print sixteen copies at once instead of eight.

13. We are not justified in supposing that the printing-machine has yet reached its stage of greatest magnitude and completeness. The present machines work so accurately, that inventors are already seeking for further extensions of the same power. Hitherto printing has always been effected on single sheets; but as paper is now made in very long strips, it becomes an interesting question whether the printing could take place before instead of after the cutting of the strips into sheets. Patents have been obtained, since the establishment of the "Times" machine, for three or four contrivances having this object in view.

14. Steam-printing has been here described as if it were only executed by means of cylinders; but such is not the case. Printing-presses, in which the form of type lies flat, and in which the paper is pressed down upon the type by means of a platen, are now moved by steam-power as well as worked by hand. The ingenuity of the late Mr. Cowper was advantageously shown in many inventions relating to these steam-presses.

15. When the printed sheets have been sufficiently dried

they are subjected to heavy pressure, partly to equalize