On Printing Presses and their Theory. 315 



the bottom. (16) is a bar check, which limits the revolu- 

 tion of the bar to a precise arc. The carriage part of the 

 press, which stands in front of the upright iron frame, pre- 

 sents nothing materialh' 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 con- 

 tinued, the mechanical advantage not only increases from 

 the gradual approach of the two main levers to a vertical po- 

 sition, but from the approach of AC and CD towards 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, measures have 

 been taken from an individual press, of the lines necessary 

 for the computation. When the bar was thrown back, the 

 angle ACD (of the triangle ADC formed by joining the 

 three centres of m.otion 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 

 ^raight line joining their outer extremities =2\ inches. 

 The length of AC was 3|-, 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 

 annexed to this paper, the gain of power will be found by 

 compounding the four following ratios : 24 to 3|, Cos. 1'-' 

 12' to Sin. ilS° 52', 15 to 2x2i, 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 inventor, 

 which was found nearly exact, = half an inch. Hence the 

 gain of power will be found by compounding the following 

 ratios : 24 to 3|, Cos. 1° 3' to Sin. 172°, 15 to 2xi, and 

 14 to 15 J which gives a result of 763 to 1, 



