86 CHRONOMETERS. 



wards and forwards, or to vibrate; and if it were not 

 connected with the fork X U, its motion would con- 

 tinue until destroyed gradually by the resistance of 

 the air and the friction on the point of suspension. 

 But as it is joined by the fork to the axis rs of the 

 pallets, it receives at each vibration a new impulse, 

 which preserves its motion, and it therefore con- 

 tinues to vibrate. Now, as all the vibrations of a 

 pendulum are performed in the same time, the 

 motion of the pallets will be uniform, and conse- 

 quently they will not suffer the teeth of the scape 

 wheel to pass in an unequal manner. Hence the 

 pendulum is the exact regulator of the motion of 

 the scape wheel, and consequently of the whole 

 train of wheels connected with it. This ingenious 

 combination of the scape wheel and the pallets, is 

 called the scapement. As this is a most important 

 part of a clock, various forms of scapements have 

 been invented to insure greater accuracy. That 

 represented in fig. 1. just referred to is called the 

 crown wheel and verge scapement, from the resem- 

 blance of this wheel to a royal diadem. It is the 

 oldest scapement, and used chiefly in common 

 watches and table-clocks. So far we have shown 

 how an equable motion of the machinery is insured. 

 It remains next to point out in what way this is 

 employed to divide and show the time. 



As it is known that all the vibrations of the 

 same pendulum are performed in the same times, 

 so also is it known that pendulums vibrate in different 

 times, according to their lengths, long pendulums 

 making their vibrations in longer periods than short 

 ones. Hence the length of a pendulum may be 

 determined that shall make each of its vibrations in 

 a second of time. This length has lately been 

 accurately determined to be in London 39.13829 

 inches. 



