THE WORKS OF A ^WATCH. 379 



genius to the arts. If a bell-rope hang free, and 

 especially if a weight be appended to it, it will 

 swing a long time. If we should chance to note 

 the regularity and time of its motion, and so leave 

 it, on returning, if it move at al}, its motion from 

 side to side (or its oscillation) will be performed 

 in very nearly the same time as at first. Familiar 

 and simple as this is, it is the pendulum, and the 

 measure of time ; and we can easily comprehend 

 that if a rod, thus swung, be so appended to the 

 work of a clock, as to receive a slight impulse, 

 sufficient to keep it in motion, it will react on the 

 clock ; and if the motions of the wheels be nearly 

 in accordance with the oscillation of the pendu- 

 lum, it will preserve the motion of the whole ma- 

 chinery correct. 



Accordingly it is easier to make a clock than a 

 watch; for in a watch some substitute for the 

 pendulum must be found ; and the substitute is a 

 very delicate piece of work, called the scapement. 



The upper wheel here is the balance-wheef, 

 within which a fine hair-spring is coiled. This 

 spring is alternately pulled and let go by a motion 

 communicated to a wheel, and the spring, by the 

 regularity of its motions, answers the purpose of 



