The principal defect in the common or old fashioned press just described, consists in the effective power of the lever being uniform throughout its range of motion, requiring the pressman to exert his bodily strength to the utmost, in giving it a tug at the end of the pull ; at which time only, when the platten is down upon the form, great force becomes necessary. This disadvantage is completely obviated in the improved press invented by the late patriotic Earl Stanhope which machine we purpose describing after having explained the principle upon which its chief excellence depends, namely, the combination of levers, by which the platten is forced down upon the form of types. In the an nexed diagram a b represents a short lever, which is connected to the top of the screw which carries the platten, the shorter arm of the said lever being the radius of the screw ; its longer arm the distance between the centre of the screw to the point b. This lever, by means of a connecting rod (•, acts upon the bent lever deg, whose fulcrum is at e; and as, by this combination of the lever, the platten acts but through a small space in comparison to the space passed through by the power, it fol lows that the effect must be very powerful. But it is necessary that this effect should be at a maximum when the platten impinges upon the type, and this object is accomplished by the angular position of the levers ; for when the platten is elevated, the lever e g is parallel to the line h i, and its shorter arm ed is nearly perpendicular to the same line, and also the connecting rod c; therefore will move the rod c with its greatest velocity during the first part of the motion of the lever e g ; at which time the lever a b forms an acute angle with the line hi; consequently acts at a disadvantage in causing the revolution of the screw ; but by the time the lever e g is brought perpendicular to the line h i (when the platten impinges upon the type) the lever a 6 is also perpendicular to the connecting rod c; con sequently it will then exert its greatest influence in causing the revolution of the screw, and at this time also the power of the workman will be applied at right angles to the lever eg, therefore will produce the greatest effect precisely at the moment of impact.
The " Stanhope press" is, in other respects, a considerably improved machine. The whole frame is made of one massive iron casting, as repre sented at k k in the subjoined cut, which exhibits a perspective view of it. In the upper part of the machine a nut is fixed, into which a stout, well cut screw I works, having a conical end that operates upon the upper end of a slider m, which is fitted into a dovetailed groove formed between two ver tical bars n n of the frame. The slider has the platten o firmly attached to the lower end of it; and being accurately fitted in the guide bars nn, the platten rises and falls parallel to itself, when the screw 1 is turned. The weight of the platten and slider is counterbalanced by a heavy weight p, which is suspended from a lever, that acts upon the slider to lift it up, and keep it always bearing against the point of the screw. At g is a forked support to the railway and car riage. The carriage is moved by a winch or " rounce," with a " spit " and leather
straps, which pass round a pulley r, one strap extending to the back of the carriage to draw it in, and two others pass round the wheel in an opposite direc tion, to draw it out : a is the table on which the type is laid. The combina tion of levers in this machine, it will be observed, is precisely the same as in the preceding diagram, and their action is the same ; consequently further description of them is omitted.
The superiority of iron presses over the wooden ones may, in a great mea sure, be attributed to the extreme accuracy with which the corresponding surfaces of the platten and table are levelled. This is effected by turning them in the lathe, with a slide-rest; and this is performed with such precision that if they do not bite a hair or a thin piece of paper in every part, they are not con sidered to be finished. The advantage of true workmanship must be apparent in printing such surfaces as those of our large newspapers, and clearly bringing up every letter and dot out of perhaps a hundred thousand or more.
I Numerous alterations have peen successively made upon the Stanhope pros by the manufacturers, who magnify them to the public u being vast improvements, as increasing the Productive power of the press in a duplicate and even triplicate ratio ; but our mechanical readers will at 012C11 perceive the impossibility of the correctness of such statements : that if there be a loss of ten or fifteen per cent. of the power applied to the Stanhope press, arising from friction, &o., no modi fication whatever of the six mechanical agents can save the whole of such loss. The press may be rendered more convenient and handy, and the minor arrange ments and appendages may be also improved; indeed, we doubt not that such ameliorations have been and will continue to be introduced ; but they become perfectly insignificant and trifling when corn with the beautiful invention of the patriotic Stanhope. Amongst the alrr manufacturers of the present day of iron presses, we may mention Messrs. Ruthven, Medhurst, Cope, Sherwin, Clymer ; there are many others, we doubt not, of equal ability, who have not succeeded in making themselves as well known. All the presses that we have from time to time seen, and especially those of the manufacturers we have named, possess some peculiar points of excellence as well as defects in their mechanism, to describe and discuss which would take up much time and space. In justice, however, to the two first•named gentlemen, whose inventions possess great originality and simplicity, we must afford room for a compendious notice of the peculiar contrivances which distinguish them from all others.
In 1813 Mr. Ruthven, of Edinburgh, took out his patent, which term having expired, the invention is public property. Instead of placing the types, as was the case in all previous inventions, upon a movable carriage, they are fixed upon a stationary table, and the platten and tympana are drawn over it, and the impression is effected by a system of levers, the action of which the annexed diagram will serve to explain.