PRINTING-PRESS (Tyra) is the very important implement used for transferring the impressions of inked typos to paper. The first printing was effected by a fiat board with blows of a mallet. But the number of impressions rendered it ne cessary to convert the board into a solid platten, and carry this upon the paper, by means of a screw, and a lever to turn it. The types were inked with large balls, made of sheep's pelt, and the soft covering placed over the paper, to pro tect the types, and bring the paper into contact with the entire surface of each type ; but, in time, this has been changed into the tympan-frame of parchment and interposed flannel. Such, with some changes and varieties in the parts, is the ordinary printing-press, which takes off from 250 to 300 impressions per hour: Very little improvement in the construc tion of this instrument took place from the first introduction of the art into Europe till the late Earl Stanhope applied the powers of his mind to the subject, and introduced a new press of a decidedly superior construction. The old press was made of wood, with an iron screw that had a bar fitted in it ; to the lower end of this screw was attached, horizontally, a fiat piece of wood, called the platen, which-was brought down by means of the screw, and pressed the paper upon the face of the types ; and thus the impres sion was obtained This press has, how ever, entirely given place to presses made of iron. Lord Stanhope's press is con structed of iron with a screw ; but the bar is fixed to en upright spindle, to which a lever is attached connected with a second lever fixed to the top of the screw by a connecting bar. These two lev6rs are plac ed at different angles to each other ; and when the platen is brought down to the face of the types, and power is wanted, the two levers take such a position with each other as to act with the greatest ad vantage, and thus an almost incredible accession of power is gained, which ena bles the pressman to print larger sheets of paper in a superior manner, with less labor, and with greater ease to himself. It does not act by a continuous, but by a reciprocating motion, and can only pnnt 250 impressions per hour. This press for a long time maintained its superiority over all others.
This great improvement in the printing press that Lord Stanhope had accom plished, excited other ingenious men to exert their abilities in attempts at further improvements; among whom was a Mr. George Clymer,an American,who brought forward an iron press, called the Colum bian press, in which he discarded the screw, and obtained his power entirely by levers. This press has great power, and consequently great strength, and is made of a size to print larger sheets of paper than any other; but for the common run of printing it does not work so easy as the Stanhope press.
The common printing-press in which the impression is given by a compound lever acting on an inclined plane,is found suffi ciently' powerful to print a newspaper form of the size of 42X26 inches, having a chase 4 inches larger each way. It requires two persons to work it, one of whom inks the form with the rollers and does noth ing else. The other performs the princi pal labor, putting on and taking off the sheet, rolling the form under and from under the platen, and giving the pull, which is necessarily a heavy one. The ex ertion required to throw off 250 impres sions in an boar at a press of this size is very great, and that quantity cannot well be exceeded.
The platen power-press of the best con struction has self-inking rollers and a fly for removing the printed sheet from the type, and laying it on the heap. It is worked by two persons, one of whom, a stout man, keeps it in motion by turning a crank attached to a fly-wheel, and the other performs the light duty of putting on the sheets. The bed and platen are immense masses of cast iron, intended by their strength to guard against an inclination to spring, which is very apparent in the hand-press, and par tially corrected by making the bed and platen slightly concave on their face. The platen power-press when calculated to print a form of 42 by 26 inches, will weigh 8,090 pounds, and when worked by one man at the crank as usual, may give 400 impressions in an hour, or if greater speed be required, with the aid of a steam engine, it may be safely worked at 600 impressions per hour. It is a great improvement on the hand-press, whether used for book or newspaper printing.