On Cog or Toothed Wheels. 159 
quired. They have done more; they have 
given birth to machines of no small impor- 
tance, that could not have existed without 
them. In rapid motions they do all that band 
or cord can perform, with the. addition of 
mathematical exactness, and an. important 
saving of power. Inspinning factories these 
properties must be peculiarly interesting ; and 
in calico-printing, the various delicate opera- 
tions require great precision of motion. In 
clock-making also, this property is of great 
importance in regulating the action of the 
weight, and thus giving full scope to the 
equalizing principle whatever it be. I may 
add, it almost annuls the cause of anomaly in 
~ these machines, since a given clock will go 
with less than 3 of the weight usually em- 
ployed to move it. Another useful applica- 
tion may be mentioned; in flatting mills, 
where one roller is driven by a pinion from 
the other, there is a constant combat between 
the effort of the plate to pass equally through 
the rollers, and the action of the common 
geering, which is more or less convulsive. 
Whence the plate is puckered, and the resist- 
ance much increased, both which circum- 
stances these wheels completely obviate ; and 
many similar cases might be adduced. 
I shall only add, that my ambition will be 
