122 



HOROLOGY. 



Kscp-- the detents, so much less or more hold will the detent 

 ^ menu. pieces have of the teeth. These holding pieces of the- <lo- 

 Anothcr^ tents * not represented in the drawing, as they would 

 h ivi- nvi'le other parts of it r;ither obscure. 1 hey are 

 Vapemrnt made of stone, and are fitte<l in by means of a dovetail 

 by Mr ;'uiil. cut in a piece left for that purpose 1 , on the inside of the 

 PI.ATK detent arms, as may easily be conceived from the draw- 

 ' ' l''gs- j,,,, w here it is represented in part at c. Fig. 5 ; and 

 is in the line across the ann with the screw e, which 

 is close by the edge of the detent stone-piece, which 

 projects a little beyond the end of the screw. Having 

 described the parts of the 'scapement, we shall now ex- 

 plain their mode of action. On the left hand side, the 

 pin-tooth is represented as having just escaped its pal- 

 let, as seen in Fig. H ; but, previous to its having got 

 on to the flanch of this pallet, let us conceive that the 

 bark of the pallet, or end piece h of it, had come, in 

 consequence of the motion of the pendulum, to that 

 side, and opposing the screw e, which is in the detent 

 arm, pushes or carries it on with it, and consequently 

 unlocks the tooth of the wheel which then endeavours 

 to get forward ; but the pin-tooth, at this instant of un- 

 locking, meeting with the flanch of the pallet at the low. 

 er edge inside, and pushing forwards on the flanch, by 

 this means impels the pendulum, and after having es- 

 caped the pallet, the next locking tooth is received by 

 the detent on the right hand side, where the wheel is 

 now again locked. In the mean time, while the pen- 

 dulum is describing that part of its vibration towards 

 the left hand free and detached, as the pallets are now 

 at liberty to move freely and independently of the 

 small pin-teeth, on the return of the pendulum to the 

 right hand side, the detent, by means of the back of the 

 pallet on that side, is pushed out from locking the 

 wheel, and, at the instant of the unlocking, the wheel 

 gets forward, and the pin-tooth is at the same instant 

 ready to get on the flanch of its pallet, and give new 

 impulse to the pendulum, as is obvious by what is 

 represented in the drawing, Fig. 3. After the pin- 

 tooth has escaped the pallet, the wheel is again lock- 

 ed on the opposite or left hand side; the pendulum 

 moves on to the right freely and independently till the 

 next locking on the left takes place, and so on. It may 

 be observed, that the unlocking takes place when the 

 pendiJum is near the lowest point, or point of rest, and 

 of course where its force is nearly a maximum. Without 

 attaching any thing to the merits of this 'scapement, we 

 may remark that the clock was observed from time to 

 time by a very good transit instrument, and, during a 

 period of eighty three days, it kept within the second, 

 without any interim apparent deviation. This degree" 

 of time-keeping seemed to be as much a matter of ac- 

 cident as otherwise ; and cannot reasonably be expected 

 from this, or any clock whatever, as a fixed or settled 

 rate. 



Method of This 'scapement being a detached or free 'scapement, 

 tuT'sca"!: can at P^ easure be converted either into a recoiling or 

 mcnt either a ^ eat ' beat one, without so much as once disturbing or 

 into a re- stopping the pendulum a single vibration. To make a 

 coiling or a dead beat of it, put in a peg of wood, or a small wire to 

 dead-beat each, so as to raise the detents free of the pallets ; and 

 these being left so as to keep them in this position, the 

 pin-teeth will now fall on the circular parts of the pal- 

 lets, and so on to the flanch, and the 'scapement is then, 

 to all intents and purposes, a dead beat one. To make a 

 recoiling one of it, let there be fixed to each arbor of the 

 detents, a wire to project horizontally from them about 

 3 or 4 inches long ; the outer ends of the wires must be 

 tapped about half an inch in length; provide two small 

 brass balls, half an ounce weight each, having a hole 



through them, and tapped so as to screw on the 

 wires; the bulls can be put more or less home, and be mems. 

 adjusted proportionably to the force of the clock on the " """Y" 

 pendulum. No recoil will be seen by the seconds' hand ; 

 yet these balls will alternately oppose and assist the mo- 

 tion of the pendulum, as much as any recoiling pallets- 

 can possibly do; and as their effects on the pendulum 

 will lie exactly the same, it may be considered as a good 

 recoiling 'scapement. This sort of detached 'scapement, 

 by becoming a dead beat, or a recoiling one, at any time 

 when required, makes it convenient for making various 

 experiments with the different 'scapements. 



We shall now proceed to describe a clock 'scape- 

 ment, whose pallets require no oil, invented by the late 

 Mr .John Harrison, who received the parliamentary 

 reward of 20,000 for a marine time-keeper. 



In Plate CCCI. Fig. 6. S W is the swing-wheel, Harrison's 

 whose teeth are shorter than usual. On the verge is a' clock 

 brass arm, of a sort of cross and flat pronged form, as es P eme 1J 

 may be seen at e, e, e, Fig. 6. and at e, e, Figs. 7- and 8. *', ^" E 

 Upon this arm are screwed two brass-cocks, marked d, d, CCCI. Fig?. 

 in Fig. 6. and d in Figs. 7. and 8 ; the upper pivots of 6', 7, 8. 

 the pallet arbors, as seen at a, Figs. 7. and 8. run in 

 these cocks, and the lower pivots in the end of the 

 prongs. On the lower end of the pallet arbors is a 

 brass socket to each, having freedom to move easily on 

 them, and also a proper end-shake between the prongs 

 and the pallet arms. On the end of the sockets, next the 

 pallet arms, is rivetted a thin piece of brass to each, the 

 piece on the socket of the driving pallet being shaped as 

 seen at h, h, Figs. 6. and 7- and having two holes in it : 

 one of these holes has a range, limited by a pin fixed to 

 the brass arm from the verge ; the other hole, which is 

 at the outer end, allows range to a pin, which is fixed 

 to an arm on the pallet arbor, as may be seen at Figs. 6. 

 and 7. The piece of brass on the socket of the leading 

 pallet arbor is shaped as seen at k, k, Figs. 6. and 8. 

 having a tail which comes to rest on the outer edge of 

 the cock d, after being carried a little way by the mo- 

 tion of the pallet ; at the outer end, at k, is a small 

 brass screw, serving as a counterbalance to the opposite 

 arm or pallet hook. In this pallet arm is an opening, 

 through which the swing- wheel comes, as may be seen at 

 I, Fig. 8. the arm at the other end being filed thin down, 

 leaving a sort of shoulder on it. AB, Fig. 6. is a stout 

 piece of brass rivetted, or screwed, to the verge collet; 

 CC is the steel crutch, having another arm, which comes 

 up on the inside of the piece of brass ; the ball or paume 

 of the crutch is kept to the verge collet by a sort of 

 spring collet, which has two screws outside, and through 

 to the verge collet, the crutch having liberty to turn 

 on the verge. The piece of brass AB has two short 

 knees turned up, having a hole tapped in each to re- 

 ceive the two screws s, s, Fig. 6. whose ends bear on 

 the upper arm of the crutch, and serve to move the 



arm to one side or the other, so as to put the pendulum 

 or clock on beat ; p, p, is a piece of hard wood pu 

 the lower end of the crutch, having an opening in it, 



put ori 



to clip or take in with the middle rod of a gridiron pen- 

 dulum. 



The parts of this 'scapement being described, it now Mode of ac- 

 remains to explain their action. The tooth of the tion in Har- 

 swing- wheel, which has hold of the hook of the leading 011 ' 8 

 or right hand pallet, carries it on, until another tooth e ' 

 meets with the hook or notch at the end of the 

 driving pallet arm. When this takes place, the wheel 

 is made to recoil a little back; at this instant, the 

 hook of the leading pallet gets free of the tooth, and is 

 made to rise clear of the top of it, by means of the 

 counterbalancing of the brass arm, and the screw k at 



