HOROLOGY. 



149 



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ty, which U a little inclined : But the spring il tending 

 to bring back the arm o, the inclined plane obliges the 

 pin to describe still a small space, which takes the arm 

 (Fig. 1.) entirely out of the reach of the pins, so 

 that the hammer cannot strike unless the pin is disen- 

 gaged from the end of the arm o. To effect this, the 

 arm of the rack must come and press on the snail L, 

 which moves on a stud V, fixed to the all or nothing piece 

 TR. Now, in pressing the snail, the arm o of the pin 

 is set aside, which getting free, gives liberty to the 

 arm m to present itself to the pins of the wheel G, and 

 to the hammers that of striking the hours and quarters 

 given by the dial work and hands. 



The ratchet R (Fig. 3.) is that of the click and ratchet 

 work of the movement ; c is the click, r the spring. 

 The ratchet R is pat on a square of the barrel arbor ; this 

 square being prolonged, serves to wind up the spring by 

 means of a key ; B is the barrel in which the spring or 

 motive force for the repetition must be put ; ' 

 screw, called the eccentric or pivot carrying piere : 

 On the part which enters with force into the plate, 

 a little out from the centre of the arbor of the screw 

 a hole is made f.>r the pivot of the anchor A. In 

 nuking this screw turn, the pivot of the arbor of the 

 anchor is made to go farther < nearer the centre, and 

 consequently the anchor it-elf', so that the points of the 

 pallets take more or less in, according as is required 

 with the teeth of the scapement wheel. A, Fig 

 the cock of the 'scanement, it carries the >ilk thread 

 or spring, to which the pendulum is suspended. One 

 of the ends of the silk thread is attached to the arbor c, 

 which is called armer or reforrf, (fast or slow); the 

 other end of this arbor goes through to the dial, and 

 is squared, to receive a small key. By this meanv we 

 can rum the arl>or e to any side, so as to lengthen 

 or shorten the silk thread, which serve* tn up. -ml the 

 pendulum, whose length is changed by thi met! 



The anchor A fixed on an arbor similar to 



that for a second* pendulum. This arbor carries the 

 fork T, which gives motion to the pendulum. The pi- 

 vot which this arbor carries at the end where the fork 

 is, enter* into a hole made in the cock A, Fig. 2. 



4. represents in perspective the wheelD, whose 

 >tion i< performed in an hmir ; it i the arbor of 

 it that carries the wheel m of Fig. S. This wheel m 

 is seen in pertpertite in Fig. 5. who*e cannon serves to 

 carry the minute hand. Fig. 8. rtpitsaiiu in perspec- 

 tive the wheel S of Fig T It n the arbor of this 

 wheel prolonged, which passing to the motion work, 

 carries the quarter snail k. Fig. 2. The pinion of this 

 wheH S. pitches into the hoar wheel, seen in perspec- 

 tive in Fig. 7 ; and it is on tho socket of thai wheel, 

 that the hoar hand is adjusted or bed. 



It will be soon from the preeadhw d 

 the 



movement, or which serve to measure the time, as the 

 wheels B, C, D, E, F, and those of the repetition, which 

 serve to regulate the interval between the blows of the 

 hmmer: such are the wheels a, b, c, d, e,f, whose 

 assemblage is called the little wheel work, or runners. 



The spring of the movement is contained in the bar- 

 rel A ; B is the great or fusee wheel ; C the centre or 

 second wheel, whose arbor prolonged carries the cannon 

 pinion on which the minute haml is fitted and adjust- 

 ed ; D is the third wheel ; E the fourth wheel ; and F 

 the cylinder, 'scapemeni, or balance wheel. The fusee 

 I is adjusted on the great wheel B, a spring-tight col- 

 let and pin keeping the wheel to its place on the fusee ; 

 the chain is wound round on the fusee, and holds like- 

 wise of the barrel. The hook O of the fusee serves 

 to stop the hand, on the watch being full wound up, 

 by the hook stopping against the end of the guard de 

 gut stop (the name it got before the chain was put to the 

 ftisee; the modern name of it is the fusee stop,) C( Fig. 2.) 

 attached to the other plate ; its effect is the same as in 

 the plain watch. Fig. S. of PlateCCCII. represents 

 the cylinder 'scapement, of which a description has al- 

 rcady been given in p. 127- 



B is the balance fixed on the cylinder ; F is the cy- 

 linder wheel, which is represented as tending to act on 

 the cylinder, and cause vibrations to be made by the 

 balance. None of the pieces are drawn here, such as 

 the cock, slide, curb, and pendulum or spiral spring, 

 as they would have rather made the 'scapenient part 

 obactire. The wheel work, or runners of the repetition, 

 i* composed of five wheels, a, 6, c, d, e, and of the pi- 

 and of four other pinions. The effect of this 

 wheel work U to regulate the interval between each 

 blow of the hammer ; so that if the first wheel a is made 

 to have * teeth, the second b 36, the third c S3, the 

 fnarth rf SO, and the fifth e 25 ; and moreover, if all the 

 pinions into which these wheels pitch have six leaves 

 or teeth ; then in the time that the first wheel a makes 

 a turn, the pinion /"will make 4812} revolutions; but 

 the ratchet R. which the first wheel a carries, is com- 

 d into 24 parts, the half of which are after- 



. 

 preceding description, that 



niece* of the repeating motion work are here placed 

 i die bark of the pillar plate. Placing them on the 

 plat* will make no difcrence. 



hall now proceed todesrribe a repeating watch 



with a horaontal or cylindrical 'scapement of Graham's. 



What has been said concerning the repetitions hi 



pendulom docks, and the simple or plain watch, bo- 



ing once wen understood, the reader will h.i 



watch, which is only on a imli what theltecku 

 on a great scale. 



Fig. I. of Plate CCCVI. represent, the wheel-work 

 of the movement and of the repetition, and all the 

 piece* which are put within the hsias plaUi. There 

 M a ilsUJmiiun here between the h-rl, those of the 



ccCVi. 

 Fig. 1. 



monl 



wards taken away, in order that there may remain only 

 12 to strike 1C bfows for the 12 hours. If. then, we di- 

 vide 48 12 by 24, we shall have the number of turns 

 that the fifth pinion makes for each blow of the ham- 

 mer, which gives 900^ tarns of the pinion f for one 

 tooth of the ratchet R. 



The first wheel a, or great wheel of the striking part, 

 carries a click and a spring, on which act a small ratchet, 

 put under the ratchet wheel R, which forms click and 

 ratchet work, like what has been seen in the first wheel 

 of the repetition (IM.it. < i < \ Fig. I.], which has the 

 same u-<- ; th.it i tn <ay, when we push the pendant or 

 poshtr, the ratchet R retrogrades, without the wheel a 

 turning ; and the spring which is in the barrel B (Fig. 

 2. ) bringing back the ratchet R, on whose arbor p, tin- 

 inner end of the spring in hooked ; the small ratchet 

 comes butt against the click, and turns the wheel a ; 

 and the ratchet R makes the hammer M to strike, whose 

 arm m is engaged with the teeth of this ratchet. 



The spring r attached to the plate (Fig. 2.) acts on 

 the omall part a of the arm m (Fig. 1 . ) The effect ut 

 this spring is to press the arm m against the teeth ot 

 the ratchet ; so that when we make the watch to re- 

 peat, the ratchet R retrogrades, and the xpring r brings 

 always back the arm m, in order that the teeth of the 

 ratchet may make the hammer to strike Let us now 

 iss on to the description of the motion work. 



Plate CCCVI. Fig. 3. represents that pan of a repeat. Fig. 3. 



