On Printing Presses and their Theory. 311 
MECHANICS AND ARTS, CHEMISTRY AND PHYSICS. 
— 
_Art. [X.—On some recent improvements in the constructioit 
of the Printing Press; with a particular notice of that 
lately ec lid His Mr. John I. Wells, of Hartford, Ct. 
by A. R, Professor of Mathematics and Natu- 
ral Philosophy ¢ in Yale College. 
Tue principal defect in printing presses of the ordinary 
construction, so far as the mechanism employed to procure 
a gain of power is concerned, consists in the want of adap- 
tation of this power to the variable resistance which is to 
overcome. ‘The elastic substances interposed between the 
form of types and the platen, present at first a compara- 
tively trifling resistance ; but it gradually increases as the 
platen descends, and must finally be made immensely 
fe . S, order to attach the ink with sufficient firmness to 
the r. ~But to overcome this resistance the mechanical 
advunniee furnished by the screw is perfectly uniform. To 
make up for the want of an increasing advantage in pte me- 
chanism, the pressman is obliged to place his body in 
an attitude ‘that his weight shall conspire with the fakes ¢ of 
his muscles, and to exhaust on the bar as much motion as 
he can accumulate in a pull of three feet, in order to give it 
_a species of percussive effect. Hence the employment of 
pulling at the common press has been always regarded as 
one of the severest kinds of labour; nor has it been — 
sented without reason as often “ destructive of health and 
life.’ 
It has long been an object with those interested in the 
improvement of the art of printing, to introduce into the 
press a variable power, which shall increase with the resist- 
‘ance to be overcome, and thus render the pull on the bar « 
nearly equable one throughout. The earliest contrivance 
for this purpose which appears to sat eso been in any Searce 
successful, was that of Mr. Ravorth London printer.* In 
his press the screw was di ispensed ivi at ene ndle> 
substituted in its place. To the under side of the head or 
* See art. Printing, hea? Cyc. fora ate fol account of this coneteceti 
