f On Printing Presses and their Theory. 317 



must not be supposed however that this ratio is a fair crite- 

 rion of the total strength exerted. This is probably about 

 half or f as great, in the former as in the latter. When a 

 pressure is to be produced between the paper and form of 

 types of from 25 to 35,000 pounds, it is not in the power of 

 mechanism to supersede the application of a considerable 

 aggregate force to the bar. The superiority of the Lever 

 press lies much more in the equalization of the force which 

 it occasions, than in the reduction of its total amount. It is 

 true at the same time that the Lever press does considerably 

 diminish the total force of the pull ; but it is chiefly by per- 

 mitting a diminution in the thickness of the elastic substan- 

 ces which form the tympan, and dispensing with the spring 

 of the summer, — not from the peculiar nature of the mechan- 

 ism which effects the gain of power. 



By admitting the two main levers (6) and (17), or the 

 two horizontal ones AC and CD to come much nearer to a 

 straight line, a far greater mechanical adv^antage might have 

 been obtained ; but it would have been of no practical use. 

 The inventor has righily judged that it is time to stop the 

 bar when it begins to move sensibly easier. If it were per- 

 mitted to go further, the platen could descend but an ex- 

 tremely minute interval, and consequently the elastic re- 

 action of the tympan and blankets would remain nearly sta- 

 tionary. At the same time, the positive disadvantage would 

 be incurred of rendering it impossible for this elastic force 

 to produce the return of the bar. 



There are a variety of circumstances relating to the Lever 

 press, aside from the peculiar nature of the power it em- 

 ploys, which recommend it to the attention of the owners of 

 printing establishments. 



1. The force exerted being exactly gauged by the pin 

 which stops the bar, the impression of different successive 

 sheets will be absolutely uniform, except the trifling and 

 scarcely perceptible difference which may arise from the 

 variable thickness of the paper. 



2. For the same reason, the pressman will find it much 

 less easy, if disposed, to do his work imperfectly. Indeed 

 from the superior facihty with which the press is worked, 

 the temptation to shght his task is in a great measure re- 

 moved. 



3. The whole of a form being worked at once, and the 

 platen admitting a superior evenness of surface and exac.t- 



