On Printing Presses and their Theory. 317 
must not be supposed however that this ratio is a fair crite- 
rion of ne total veees* exerted. This is probably about 
half or 3 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 ¢otal force of the pull; but it is chiefly by per- 
mitting a diminution in the thickness of the elastic substan- 
nae _which f form the tympan, and — — the ares 
nature of 
ism which effects the gain of powe 
By admitting the two main ies (6) ral: an, os tie 
two horizontal ones AC and CD to come much nearer to a 
ight line, a far greater mechanical advantage might have 
hean obtained ; but it would have been of no practical use. 
The inventor has rightly judged that it is time to stop the 
bar when it begins to move sensibly easier. If it were per- 
mitted t to go mi the aan could descend but an ex- 
ry. At the same time, the positive antage V 
be incurred of rendering it impossible for this elastic ise 
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- - 
este which recommend it to the attention of the owners ners of 
od 
m3. The whole of a ‘Eck eee ied sions an the 
platen admitting a superior evenness of surface an d exact- 
