The mode in which the movement of the working bar (12) is transmitted to the main levers, will he best under stood from Fig. 15, which is a representation of the parts 11, 12, 13, and 15, as they would appear to an eye looking down upon the press from above. The bar BA (the lever worked with the hand) is inserted into a strong cast iron roller (13) which turns in sockets 'seeured to the right cheek of the press. From this roller, about six inches above the bar, proceeds an arm AC, three inches in length, and to the extremity of this is connected by a joint the driving lever CD, 211 inches long. The extremity D is connected in a similar way with the iron rod EF ; one end slides in a pewter guide, (represented by 10 in Fig. 14,) while the other end is fastened by a hook arid eye to the upper main lever (6) at the distance of an inch from the bottom. (16) is a bar check, which limits the revolution of the bar to a precise arc. The carriage part of the press, which stands in front of the upright iron frame, presents nothing materially different from the Columbian press, and will not require a particular description.
The operation of the mechanism will now, it is believed, be sufficiently apparent. When the bar BA is brought round the roller A and the arm AC are made to turn with it ; this drives forward the lever CD, and this in its turn gives motion to EF, which, by means of the elbow at F, brings the two main levers (6) and (17) towards the posi tion of a straight line. As the movement of the bar is continued, the mechanical advantage not only increases from the gradual approach of the two main levers to a vertical position, but from the approach of ACACD to wards a straight line. The combination is therefore one which is eminently adapted to effect that rapid increase of power, near the end of the pull, which has been already mentioned as the great desideratum in the construction of this part of the printing press.
To determine the actual gain of power at the beginning and at the end of the pull, measurements have been taken from an individual press of the lines necessary for the com putation. When the bar was thrown back, the angle ACD (of the triangle ADC, formed by joining the three centres of motion with straight lines) was found to be — 113° 52', CDA = 7° 12', and the distance of the centre of motion of the two adjacent ends of the main levers from the straight fine joining their outer extremities — 24 inches. The length of AC was 3i, and the distance from A to the part of the handle where the hand was generally applied was 24 inches. Hence, as will appear from the theorems given above, the gain of power will be found by compound ing the following ratios: 24 to 3; cos. 70° 12' to sin. 113'
52' ; 15 to 2 X 2i ; and 14 to 15; which gives a total of 20 to 1.
At the end of the pull the angle ACD = 172°, the angle CDA = 1° 3', and the distance of the vertical levers from a straight line, according to the specification of the inven tor, which was found nearly exact, = half an inch. Hence the gain of power will be found by compounding the fol lowing ratios : 24 to 31- ; cos. 1° 3' to sin. 172° ; 15 to 2 X ; and 14 to 15; which gives a result of 763 to 1. It thus appears that the power gained is about thirty-eight times greater at the end than at the beginning of the pull." Hope's Printing Press.
One of the latest printing presses is that invented and constructed by Mr. Hope of Jedburgh, who has secured it by a patent. This press, which is represented in Fig. 9, is an improvement on the Stanhope press; and the patent is taken out merely for a new combination of levers. A plan of that part of the press is shown in Fig. 10, where a, a are the iron standards of the press, and b the platen, with the form of types under it. The handle d of the press is attached to the short arm, or lever e, turning on a pivot in the pillar a. The connecting rod f is fixed to e by a joint, and in the usual construction of the Stanhope press, it is connected to another short arm fixed to the metallic screw or bolt in the joint of the press. In the present new construction, however, the rodf is connected by a joint to one arm of the forked lever g, which moves upon a cylin drical fulcrum on the pillar a, while the other end is joined by a pivot to the posterior rod /2, jointed to a short arm i, extending from the bolt of the press. Mr. Hope therefore gains additional power, by using the additional connecting rod h and the bent lever g.
When the press is at rest, the combination of levers has the position shown in the figure; but when it is in action, the path described by the different parts is shown by the dotted line.
In place of the male and female screws by which the platen generally rises and falls, he substitutes two inclined planes ; but these do not for,n a part of his patent.
This press has been used in' several printing offices both in England and Scotland, and it is admitted to unite the advantages of cheapness with great power and accuracy.
Several other presses have been contrived. In Brown's press, for which a patent was taken in 1807, the screw is moved by a bevelled wheel and pinion, and the types are inked by two classic rollers. Brookes's press consists in the application of the compound levers of the Stanhope press to the common press.