274 



CLOCK-WORK. 



one end, being suspended at the other. The length of 

 time which the pendulum takes to vibrate will depend 

 on its length, that is, on the distance between the cen- 

 tre of suspension and the centre of gravity of t lie bob. 



On the laws of the motion of pendulums, such 

 remarks shall only be made here as are necessary for 

 the illustration of the movement of clock-work. The 

 length of a pendulum vibrating seconds at London 

 hits UTII found to be 3!)-i:)'.):l inches. This pendu- 

 lum, although vibrating seconds at London, would 

 not do so correctly in other latitudes, for it has been 

 found by experiment, and may be demonstrated from 

 the known laws of gravity, that the length of the 

 .seconds' pendulum, increases by a certain rate, as we 

 :ul\a nee from the equator to the poles, the length 

 at the equator being 39, and at the poles 39-206 

 i in -lies. The latitude of the place where the clock 

 is meant to go must therefore be taken into considera- 

 tion by the maker, and the length of the pendulum 

 regulated accordingly. The pendulum may be made 

 to vibrate half-seconds, seconds, or two seconds, and 

 the number of the teeth in the wheels made to cor- 

 respond ; but when a choice can be made, experi- 

 ence proves that preference ought to be given to a 

 long pendulum. On this subject more shall be said to- 

 wards the end of this article ; meantime we return 

 to the examination of the connexion of the pendulum 

 with the swing-wheel. When the pendulum y B,fig. 

 1, is drawn a Tittle aside from the perpendicular, and 

 then let go, it will move backwards and forwards, the 

 bob B describing the arc of a circle round the centre of 

 suspension y ; and from the connexion before pointed 

 out between the pendulum and the pallets, IR, fig. 2, 

 it is easy to see that when, by the action of the weight 

 P, motion is, as shown before, transmitted to the 

 wheel GH, a tooth, H, of this wheel will act upon 

 the pallet R, move it, and cause that tooth to es- 

 cape. The motion of the pendulum will then cause 

 the pallet I to come into contact with the tooth G, 

 which again will escape, and so on, each tooth in the 

 wheel escaping the pallets. This department of the 

 clock is denominated the escapement. Various forms 

 of tlie escapement have been employed at different 

 times, many of which exhibit great ingenuity ; tliat 

 which we have just described is the one in common 

 use ; it is very simple, and answers all ordinary pur- 

 poses sufficiently well. In tracing the times of the 

 revolutions of the wheels, we refer to fig. 1, where 

 the wheel EE revolves once in an hour. The pivot 

 c of this wheel passes through the plate, and is 

 continued to r, upon which the minute hand is fixed. 

 This extremity r, which carries the. minute hand, is 

 the end of a long socket fastened into the centre 

 of the wheel NN, the teeth of which act upon 

 the wheel O, whose pinion p moves the wheel gg 

 fixed upon the socket which turns with the wheel 

 N. The hour hand is fixed upon the barrel of the 

 wheel gg, which of course turns once round in 

 twelve hours. 



from this description, the reader will perceive that 

 the whole of the wheels, as likewise the pendulum, 

 ore kept in motion by the descending of the weight 

 P . until the cord which is coiled round the barrel has 

 been run out. The clock is again wound up by 

 means of a key which fits on the square end of the 

 arbor Q. 



For the purpose of winding the clock, the click c, 

 fig. 2, is moved by the inclined side of the teeth of 

 the ratchet wheel K, which turns v/ith the barrel, 

 while tlie wheel D is at rest, but it continues to 

 move so soon as the cord is coiled upon the barrel 

 the click falls and checks the teeth, thus allowing the 

 wheel D .to move, the click being kept in the teeth 

 of the wheel by means of the spring A. If the 

 pendulum of the clock be a seconds' pendulum, it 



will make 3(100 vibrations in an hour; but a halt 

 seconds' pendulum, whose leiith is about 9^ inches 

 long, will make double that number, f. e. 7200 vi- 

 brations in an hour ; and, .supposing the latter to !* 

 employed, it then follows that, since tlie teeth of the 

 swing-wheel GH must all act on cn.-li of the pal- 

 lets, each tooth causing one vibration of the pen- 

 dulum, if the swing-wheel have 30 teeth, the pen- 

 dulum will make 60 vibrations during one of its 

 revolutions. Hence since 60 is continued in 72<V> 

 120 times, the wheel GH will turn m times in ;m 

 hour. If the wheel E have 72 teeth, and the pin- 

 ion 6, then will the pinion revolve 12 times f. i 

 one revolution of the wheel. The pinion c turn- 

 the wheel F which has 60 teeth, and the pinion <> 

 making ten revolutions for one of the wheel F, make* 

 120, while E performs one. The pinion / moves 

 GH, causing it to turn round and make the pendu- 

 lum vibrate 60 times for every revolution ; and as the 

 pinion/ turns the wheel G, the pendulum must make. 

 60x 120 or 7200 vibrations, while the wheel E makes 

 one turn. This last wheel, then, turns once in an 

 hour. The wheel N on the same axis must like\\ isc 

 turn in one hour, and the minute hand is fixed upon 

 a tube on the axis of this wheel. This is fixed on 

 pretty tight, so that the hand, being carried round by 

 friction, may be moved so as to be set at any figure 

 on tlie dial plate without affecting any of the wheels. 

 The wheel N having 30 teeth, drives the wheel O, 

 having the same number, which therefore revolves 

 hi an hour. O carries the \ inion P of six leaves, act- 

 ing upon the wheel gg of 72 teeth ; and the pinion 

 will therefore make twelve turns for one of the 

 wheel gg, which must take twelve hours to revolve, 

 and upon the axis of this accordingly the hour hand 

 is fixed. 



We have hitherto confined our attention to the going 

 or watch part of the clock, we will now endeavour to 

 explain the construction of the striking department. 

 The prune mover of the striking department, is a 

 weight, attached to a cord wound round a barrel, in fig. 

 2, similar to the barrel in the clock department. The 

 wheel h, on this barrel, turns a pinion of eight leaves, 

 fixed on the same arbor as the wheel i, which aguin 

 turns a pinion of eight leaves, on the arbor ol the 

 wheel k, of 48 teeth. On the same arbor with 

 the wheel t of 48 teeth, there is fixed a pin- 

 ion driven by tlie wheel k, and the wheel t again 

 drives another pinion of six leaves, on whose axis a 

 broad flat piece of metal S is fixed, called tlie fly, 

 which, in revolving, strikes the ah*, and the resist- 

 ance thence arising retards the motion of the train. 

 Eight pins project from the side of ", which, as the 

 wheel turns round, act in succession on the tail of 

 the hammer, causing it to move out from the bell. 

 When a pin leaves the tail of the hammer, it is re- 

 turned, and made to strike the bell x, by the action 

 of the spring z. But to prevent the hammer from 

 continuing to press upon the bell, and thus deaden 

 the sound, a small spring, u, acts upon the hammer, 

 just before it strikes the bell, and lifts it after it has 

 struck. Tlie pin-wheel t, carries a pinion of eight 

 leaves, driven by the wheel A, of 78 teeth, turn- 

 ing once in twelve hours. On the arbor of tlie 

 wheel AT, which passes through the brass plate SS, is 

 fixed a small pinion of one tooth, called the gather- 

 ing pallet seen at r, fig. 3. The gathering pallet, 

 which revolves once for each stroke of the hammer, 

 turns a larger wheel, a segment of which is seen at s 

 this wheel is called the rack, and to it is attached the 

 arm b, whose end rests upon the spiral plate v, call 

 ed the snail, fixed on tlie same tubular arbor as the 

 wheel 72, and the hour hand. The snail is 

 divided into 12 parts or steps, each of which cor- 

 responds to an hour; their circumferences are parts 



