CHRONOMETERS. 9S 



cessary that the swing-wheel should have 60 teeth ; 

 whence -bb- =7^0, the number to be broken into 

 quotients for finding the number of teeth for the 

 other wheels and pinions. 



The wheels composing the going part, or clock 

 part, are: — the great or first wheel E, (Plate 5. fig. 8.) 

 which is moved by the weight or spring at the 

 barrel D : in sixteen or thirty-hour clocks, this has 

 usually pins, and is called the pin wheel ; in eight- 

 day pieces, the second-wheel, L, is commonly the 

 pin-wheel, or striking-wheel, which is moved by 

 the former. Next the striking-wheel is the detent- 

 wheel, or hoop-wheel, m, having a hoop almost 

 round it, wherein is a vacancy at which the clock 

 locks. The next is the third or fourth wheel, 

 according to its distance from the first, called the 

 warning-wheel n. To these must be added the 

 pinion of report z, which drives round the locking- 

 wheel, called also the count-wheel, ordinarily with 

 eleven notches in it, unequally distant, to make the 

 clock strike the hours. Besides the wheels, to the 

 clock part belong the ratch ; a kind of wheel with 

 twelve large fangs running concentric to the dial- 

 wheel, and serving to lift up the detents every 

 hour, and make the clock strike; the detents, or 

 stops, which being lifted up, and let fall, lock and 

 unlock the clock o in striking; the hammer s, which 

 strikes the bell R ; the hammer-tails T, by which 

 the striking pins draw back the hammers ; latches 

 whereby the work is lifted up and unlocked ; and 

 lifting pieces, as P, which lift up and unlock the 

 detent O. 



The method of calculating the numbers of a 

 piece of clock-work is as follows: 1. Regard need 

 only to be had to the count-wheel, striking-wheel, 

 and detent-wheel, which move round in this pro- 



