WATCH. 



caufes this piece D to move on its centre of motion, [viz. 

 the fcrew i ) ; its oppofite end is then prefled againft the 

 extremity of the all-or-nothing piece H, and caufes that 

 end of the piece to move in a direftion outwards ; con- 

 fequently the other end of the piece H, which prelTes 

 againft. the little all-or-nothing piece I, is moved inwards : 

 the neceflary effeft of this motion in the all-or-nothing 

 piece H, is, from the (hape of the two pieces, to caufe 

 the little all-or-nothing piece to move outwards from under 

 the arm 8, of the piece K ; and this aftion is called 

 the tmlocking of the motion. The piece I being thus, by 

 the aft of unlocking, difengaged from under the arm 8, 

 of the piece K, this piece K, by the power of the fpring q, 

 depreffes the hammer-tails, and brings them into tlae fame 

 planes as the two ratchets, and confequently into a fitua- 

 t!on to be afted on by thefe ratchets : after the itriking 

 is completed, the piece I is returned by the quarter-rack 

 into its former fituation, and with it the piece K, and 

 the two hammer-tails neceflarily refume their fituations. 

 It is to be obferved, that the all-or-nothing piece H afts 

 upon the little all-or-nothing piece I, very nearly at its centre 

 of motion i, and on the end oppofite to that which paffes 

 tinder the arm 8, of the piece K. 



We come now to defcribe the wheels that carry the 

 hands, commonly called the dial-work, and their mode of 

 communication, together with the two fnails attached to 

 them, which determine the hour and the quarter, or half- 

 quarter, if any, to be ftruck. 



The arbor of the centre-wheel, which makes one revo- 

 lution in an hour, is prolonged through the pillar-plate, and 

 on this arbor the pinion w is fitted, fufficiently tight to be 

 carried round by the wheel, but not fo tight as to prevent 

 its turning on the arbor, the upper end lu only of the focket 

 of this pinion is feen injigj. i and 2, but the pinion is fully 

 reprefented, in Jig. 5, detached from the pieces with which 

 it is connefted. The centre-wheel arbor is turned with a 

 fhoulder to receive the bottom of the cannon-pinion's focket, 

 and for it to bear againft, in order to prevent the extremities 

 of its four teeth, that ftand parallel to the arbor of the wheel 

 from rubbing on the furface of the pillar-plate : the upper 

 part of its focket, above the dial, is fquared to receive the 

 minute-hand, and the hand fits down to the (houlder, formed, 

 by the reduftion of the original cylinder, into a fquare. At 

 the bottom of this pinion's focket is a collar turned out of 

 the fame piece, of which the pinion is made, purpofely to 

 receive the quarter-fnail ; and to this collar in the fame plane 

 with the quarter -rack, is the quarter-fnail G fixed by two 

 fcrewB. This fnail is cut into eight fteps, by which the 

 number of blows to be ftruck is regulated ; if the arm y 

 reaches the ftep next the centre, the ftriking ceafes with the 

 repeating of the hour ; if it only defcends to the next, or 

 fecond ftep, the watch, after having repeated the hour, re- 

 peats the half-quarter, which is invariably defignated by a 

 fingle faint blow ; if it defcends to tlie third ftep, the 

 quarter only is repeated ; if to the fourth ftep, the quarter 

 and half-quarter; if to the fifth ftep, the half hour; if to 

 the fixth ftep, the half hour and half-quarter ; if to the 

 feventh ftep, the three-quarters ; and if to the eighth ftep, 

 the three-quarters and half-quarter. Under the fnail is the 

 cannon-pinion, which communicates the motion to the wheel 

 Q of 48, and through it to the hour-hand, and which, from 

 its finp;ular ftiape, obtains the name of lantern-pinion. This 

 pinion is of a very peculiar conftruftion, and confifts of 

 four upright, equidiltant, cylindrical teeth, attached at one 

 end to the under fide of the collar, and made out of the 

 fame piece of tteel that forms the focket and collar above- 

 mentioned, as feen in^^. 5. 



Above the cannon-pinion, and refting on it, is the hour- 

 wheel S, which makes one revolution in twelve hours ; and 

 this wheel carries the hour-hand by means of n.s focket, 

 which fits on the wheel's focket prolonged through the hole 

 in the centre of the dial. To explain the mode by which 

 this wheel is made to perform one revolution in twelve hours, 

 it will be neceflary to defcribe the wheel Q of 48, fo called 

 from being cut into 48 teeth ; the hour-fnail F, with its rat- 

 chet P ; and the wheel R of communication to the hour-wheel. 

 Thefe four pieces have one common centre of motion, which 

 is a ftud X, fcrewed perpendicularly into the pillar-plate, 

 fimilar to the ftuds r and i ; the wheel of 48, to which are 

 attached the other three, is placed as clofe as it can be to 

 the plate to turn freely. To the centre of the wheel is fixed 

 a long focket, well fitted to the ftud, by which means the per- 

 feft parallelifm of the wheel's p'ane to the furface of the 

 plate is preferred : from the face of the wheel upwards, 

 equal to the thicknefs of the hour-fnail, this focket is left of 

 a confiderable diameter, equal to the hole in the centre of 

 the hour-fnail ; for on this part of the focket it is that the 

 hour-fnail fits, but not fo tight as to prevent its turning 

 cafily on the foc'ket, while its underfide bears on the upper 

 furface of the wheel : above the furface of the fnail the 

 focket is reduced in diameter to the fize of a common foc- 

 ket. The ratchet P is faftened to the hour-fnail by two 

 fcrews, and thus becomes one piece with it ; the centre of 

 the ratchet being cut out a quantity equal to about half 

 its diameter, (fee ^g. 6,) and it is fo placed on the 

 hour-fnail, that the fmall circk- thus cut out is concentric 

 with its centre of motion. Tl-e wheel of communication R 

 (fee^^. 6. ) forms the laft of the four ; it fits tight, by a hole 

 through its centre, on the focket of the wheel of 48, and 

 on its under fide a collar is left, which fits, but not tight, 

 into the fpace formed by tlic cutting out of the centre of the 

 ratchet, and which collar bears on the (lioulder of the large 

 focket above-mentioned, that is formed by the reducing it 

 from the fize, at which it pafTes through the hour-fnail, to 

 the fmaller fize : in this manner the hour-fnail and ratchet arc 

 confined between the wheel of Q 48 and the wheel of com- 

 munication R. To enfure the fnail being carried round 

 once in twelve hours by the wheel of 48, and its being 

 prcfcrvcd in its relative fituation with refpeft to the hour- 

 hand, fo that the hour ftruck fhall accord with the hour 

 (hewn ; and alfo to enfure the fafe bearing of the arm /, of 

 the piece D, on the ftep of the fnajl, there is a notch in the 

 thick part of the ftud on which the fnail is fitted, and a cor- 

 refponding long flit, commencing at the centre of the fnail, 

 and extending nearly to its circumference ; in which flit is a 

 ftraight fpring x, that takes into the notch in the focket, 

 (feejff. 7. ) ; the efleft of this contrivance is twofold : firft, 

 by the aftion of the fpring in the notch it preferves the fnail, 

 when not aCtcd upon by the arm of the quarter -rack E, 

 conilantly in the fame fituation relatively to tlie wheel of 

 48 ; and fecondly, it allows of its being moved on its 

 centre when required, and at the fame time regulates the 

 quantity of that motion by the width of the notch in the 

 focket. The cafe in which the hour-fnail is required to turn 

 on its centre, independently of the wheel of 48, is, when the 

 minute-hand having juft paft tlie 60"', and confequently the 

 hour only being required to be ftruck, there would, without 

 this peculiar additional motion of the fiiail, be danger of 

 the arm/, which cannot be a line, but mnft polfef-i width as 

 well as thicknefs, not coming down fafe on the ftep of the 

 fnail it ought to reach, but, by being ftopped by the preced- 

 ing ftep, of its caufing the watch to repe.it one hour lefs than 

 it ft>ew8 ; to prevent this, the arm 0, of the quarter-rack, 

 when the wateh is made to repeat cxaftly at the hour, and 



I for 



