316 On Printing Presses and their Theory. 
It thus appears that the power gained is about thirty-eight 
times greater at the end than at the beginning of the pull. — 
‘While the re-action of the elastic substances which form 
the tympan is small, the mechanical advantage is small, and 
the platen is brought down rapidly ; but as the resistance 
increases, the power gained undergoes somewhat more than 
even a proportional increase, so that during the last mo- 
ments-of the revolution, the pull actually grows somewhat 
iia, In consequence of this, although the bar is stopped 
by the action of the check, nothing of that violent 
jar is produced on the arm, which is so serious an incon- 
venience in the common press; and to relieve which most 
pressmen find it necessary to sacrifice a part of the force 
exerted a et an elastic heading over the tenons of 
the summe 
Let us now compare for a moment the mechanical ad- 
vantage furnished by this combination with that furnished 
by a screw of the ordinary press. In all presses alike, 
the dicular motion of the platen may be regarded as 
to 5 this, in the screw press, we must allow at least 4 or an 
inch for the spring of the summer; making the vertical dis- 
tance described by the interior relatively to the exterior 
-screw half an inch. Then supposing the length of the pull 
to be no greater than in the Lever pr os the mechanical ad- 
vantage gained will be uniformly 44 : But if we sup- 
pose, as is generally the the case in he that the distance 
described by the hand is greater by about a foot, (although 
the increase of the distance is in reality only an exchange of 
Stine force sical. accumulated i in she sae aaa be > bat 
yz 48 great in the Lever as in the screw press; or} as great, 
if but half a form is worked at once with the latter.* It 
oe Pan ee i 
Fig ay gent tuall d the bar 
bP wend cease “tae 
