CLOCK. 



weight or bob at its lower end, in the 

 present case 39.125 inches from the sus- 

 pension D ; when this pendulum is mov- 

 ed from the perpendicular line in either 

 direction, and suffered to fall back again, 

 it swings nearly as much beyond the per- 

 pendicular on the contrary side, and then 

 returns ; this it will continue to do for 

 some time, and each of these vibrations 

 will be performed in one second of time, 

 when the pendulum is of the above 

 length. This is the measurer of the time ; 

 and the office of the clock is only to indi- 

 cate the number of vibrations it has 

 made, and give it a small impulse each 

 time, to keep it going, as the resistance of 

 the air and elasticity of the spring D 

 would otherwise in a few hours cause it 

 to stop. By the action of the weight ap- 

 plied to the cord b, (which is called the 

 maintaining power,) the wheels are all 

 turned round, and if the pallets d h were 

 removed, the spring wheel 30 would re- 

 volve with great velocity in the direction 

 from 30 to d, until the weight reached 

 the ground : the teeth of these pallets 

 are so made, that one of them always en- 

 gages the wheel, and prevents its turning 

 more than half a tooth at a time. In the 

 drawing the pallet d has the nearest 

 tooth of the wheel resting on it, and the 

 pendulum is on the side k of the perpen- 

 dicular ; when it returns it moves the 

 pallet d, so as to allow the tooth of the 

 wheel to slip off ; but in the mean time 

 the pallet A has interposed its point in the 

 way of the tooth next it, and stops the 

 wheel till the next vibration or second ; 

 the distance between the two pallets d h 

 is so adjusted, that only half a tooth of 

 the wheel escapes at each vibration ; and 

 as the wheel has 30 teeth, it will revolve, 

 once in 60 vibrations of one second each, 

 or one minute ; consequently a hand on 

 the arbor of this wheel will indicate se- 

 conds on the dial-plate F, a circle divid- 

 ed into 60 ; the pinion of eight on its ar- 

 bor is turned by a wheel of 60, which 

 consequently will turn once in seven 

 turns and a half of the other, or in seven 

 minutes 30 seconds, or one-eighth of an 

 hour ; its pinion of eight is moved by a 

 wheel of 64, or eight times itself, which 

 will turn in one-eighth part of the time ; 

 this will be an hour ; the arbor of this 

 wheel therefore carries the minute hand 

 of the clock. The great wheel of 96, be- 

 ing 12 times the number of the pinion 

 eight, will turn once in 12 hours, and the 

 barrel a with it. The' gut goes round 16 

 times, so that the clock will go eight 

 days. The hour hand of the clock is 

 turned by the wheel-work shewn in fig. 



3 : on the end of the arbor of the centre 

 wheel 64 a tube is fitted, so as to go 

 round with it by friction ; this carries 

 the minute hand, but if the clock should 

 require correction, the hand may be 

 slipped round without moving the 

 wheels ; this tube has a pinion of 40 

 teeth on its lower end, indicated by a 

 dotted circle ; this turns another wheel 

 40, of 40 teeth, which has a pinion of six 

 teeth on its arbor, turning a wheel 72, of 

 72 teeth ; the two wheels 40 will both 

 turn in an hour ; and 72 in 12 hours : the 

 arbor of this wheel has the hour-hund, 

 and is a tube going over the arbor of the 

 minute-hand, so that the two hands are 

 concentric. The barrel a is fitted to an 

 arbor coming through the plate of the 

 clock, and is filed square, to put on a key 

 to wind up the weight ; the great wheel 

 96 is not fixed fast to the arbor, but has 

 a click on ii, which takes the teeth of a 

 ratchet wheel cut upon the barrel ; so 

 that the barrel may be turned in the di- 

 rection to wind up the weight without the 

 wheel : but by the descent of the weight, 

 the wheels will be turned by the click. 



Having now described the going part 

 of the clock,itremainstodescribe the me- 

 chanism by which the hours are strwck. 

 78, fig. 2, is' a great wheel of 78 teeth, with 

 a barrel and click the same as 96 ; it 

 turns a pinion of eight ; 64 is a wheel on 

 the same arbor turning a pinion of eight on 

 the arbor of the wheel o of 48 ; th^s turns 

 another pinion of eight, and wheel p of 

 48, which turns a pinion of six, on the 

 same arbor with a thin vane of metal, 

 which is railed the fly, and by the resist- 

 ance of the air to its motion regulates 

 the velocity of the wheels. The wheel 

 64 has eight pins projecting from it; these 

 raise the tail n of the hammer, as they 

 revolve ; the hammer is returned vio- 

 lently, when the pins leave its tail, by a 

 spring m pressing on the end of a pin put 

 through its arlor, and strikes the bell, 

 (the hamirer and bell are behind the 

 plate, and therefore unseen,) / is a short 

 spring, which the other end of the pin 

 through the arbor touches just before 

 the hammer strikes the bell ; its use is to 

 lift the hammer o^T the bell the instant it 

 has struck, that it may not stop the 

 sound. The eighth pin in the wheel 64 

 must pass by the hammer tail 78 times 

 in striking tlie 12 hours, 1 -f- 2 -f- 3 -j- 4^ 

 + 54-6 + 7 + 8 + _9 + 10 + 11 -h 

 12 = 78, and as its pinion has eight 

 leaves, each leaf of the pinion answers to a 

 pin in the wheel 64 ; now as the great 

 wheel has 78 teeth, it will turn once in 

 12 hours, the same as tlie ether great 



