On Printing Presses and their Theory. 313 
er that — is a gain of power, which gradually increases 
as the two halves approach a straight line, and becomes im- 
mensely great at the moment this position is attained. The 
thrust of two such arms is precisely the same, and varies ac- 
cording to the same law for different angles, as the pull in 
the simplest case of the funicular polygon; that is, when a 
rope is tended by a certain force and is drawn aside from 
a rectilineal position by pulling at the middle. 
This principle is introduced in different forms into the 
Ruthven, Stanhope, and Columbian /presses. In that in- 
vented by Earl Stanhope it is employed to give a diminish- 
ing velocity to the screw: in the Columbian press of Mr. 
Clymer, it is employed to give a iinatatabig velocity to a 
large lever of the second kind, which is substituted for the 
screw. These two presses, especially the latter, from their 
durability, the neatness and uniformity of the im 
they produce, and the diminution of labour they occasion 
to the pressman, have been justly held in high estimation. 
To the excellence of the Columbian press, honorable testi- 
monies have been borne in foreign countries: among others 
has been a present of six thousand rubles to the inventor 
from the Emperor of Russia. 
But of all the Erasers which act on the principle of 
leverage, oe Gefaned by Mr. Wells, 
of Hartford in this ned appears to possess the highest re- 
commendations. It has now been in operation in various 
parts of the country more than two years,—a per 
ciently long to furnish an experimental test of its excel- 
lence ; and it seems due no less to the interests of the me- 
chanical arts in this country than to the ingenious pa wor 
thy inventor, that a more particular account ol it than has 
hitherto appeared should be given to the public. © 
A perspective se of this elegant piece of mechanism is 
giVeDs pinte II, fig. 1. The frame is of iron, cast (with the 
ex of the f ct), ina single ‘ages uta eae 
press pena The is of zn ie 
J ao eration. ‘The “ny 4) is cast iron, ad 1S 
of the dimensions of an entire form. ircul projec- 
tion in the middle, with six radiating pieces, gives 1t an am- 
e ei of : S the 0m acted on 
