In commencing our description of the striking parts, we should observe, that Mr. Prior not having exhibited their connexion with the going parts of a clock, we have chosen the mode of unlocking the detent which appeared the simplest, and admitted the easiest explanation ; but various other and perhaps better modes might be contrived for effecting this : the dotted circle k has a weight m sus pended from it by a catgut passing round it like that which passes round the going barrel a ; a is a scape-wheel of 78 teeth, connected with the barrel by a ratchet and click, and having 12 pins projecting from its face, a portion of which are seen, marked 2, 3, 4, 5, 6, 7, 8; these pins are ranged in a circle at unequal distances, corresponding to the number of strokes to be struck at each successive hour ; o is the scapement similar to that previously described; on its arbor is fixed a pendulum p, of about nine inches in length, and which will therefore vibrate half • seconds nearly; but in order to regulate the rate of vibration at pleasure, the rod of the pendulum is prolonged beyond the point of suspension, and carries a small ball q moving stiffly upon it and by raising or lowering this ball the vibrations become retarded or accelerated. To the lower end of the pendulum rod is attached a hammer r, which strikes upon a bell a at every second vibration ; this effect is obtained by placing the bell sufficiently oblique to allow the hammer to swing past it at one vibration, and to impinge upon it at the returning one. The barrel k and escape-wheel a are retained at rest by the locking detent t, which engages each of the pins in succession on the face of the escape-wheel ; this detent is fixed on to the arbor of the arm or lever o, which is pressed by the spring w against a snail or cam a fixed upon the hollow arbor which carries the minute-hand. The snail is consequently carried round once in an hour, during which time the lever v is gradually elevated, and moves the detent in like manner until the lever arrives at the highest part of the snail, when the pin on the escape-wheel is released from the detent, and the wheel immediately begins to revolve and imparts motion to the pendulum, which, as before said, spikes upon the bell at each second vibration. The rotation of the snail having carried its highest point past the end of the lever, the latter (pressed by the spring ro) falls past the straight side of the snail to the foot of the same, and brings the detent into its locking position • and when, by the revolution of the escape-wheel, the next pin comes in contact with the detent, the motion of the wheel is arrested. Clocks are sometimes impelled by springs instead of weights, as in the one just described, and are very convenient for placing in chambers on account of their occupying leas room than weight moved clocks. The construction of these spring clocks resembles that of the other, with the exception that for the carrel and weight are substituted a fusee and spring barrel, resembling the same pieces in a pocket-watch, to the descrip tion of which we shall now proceed.
The essential difference, as we have before observed, between a clock and a watch, consists in the former being regulated by a pendulum, and the latter by a balance ; for as to the maintaining power, it is sometimes the same in both, since although watches are not impelled by weights, clocks (as just mentioned) are sometimes kept in motion by springs hke watches. The balance is a small wheel fixed on an arbor or axis called the verge, and moving freely upon pivots at the ends of the arbor. To the axis of the balance the inner end of a very elastic helical spring called the pendulum is attached, and the outer end is made fast to some fixture. In this state the balance will remain at rest when the spring is in that position which it would assume if detached from the balance, and at perfect liberty ; but if the balance be turned on its pivots in either direction, so as either to wind up or unwind the spring, the latter will, upon the external force being removed, tend to resume its natural position ; but the momentum which is thus imparted to the balance will carry it past the position of rest, which will again alter the spring, and the balance will again be returned past the position of rest, and will thus continue to vibrate until the friction of the pivots and the resistance of' the air destroy the original impulse. The vibrations of such a balance, which passes through equal spaces, will be per formed in equal times; these vibrations, therefore, form the real measure of time, and the remaining apparatus in a watch is for the purpose of registering the vibrations, and of maintaining the motion of the balance ; and this is accomplished in watches by means of a train impelled by a spring and fusee. The spring employed for this purpose consists of a long flat plate of steel, coiled up in a helical form ' • it is inclosed ina cylindrical box called the spring barrel, to which its external extremity is attached, whilst its internal end is connected to a fixed axis, round which the barrel revolves. As the strength of the spring is greater the more it is coiled up by turning the box, its action would be unequal in impelling the work of the clock ; and to remedy this inconvenience, the fusee has been contrived. The fusee consists of a conical barrel, round
which a spiral groove is cut, which receives a chain previously wound round the barrel, by which, as it is turned round, it coils up the spring; the groove receives the chain first near the base of the cone, and as the barrel revolves, gradually brings it nearer the axis; by this means the stronger the spring is coiled up, the shorter is the lever by which it acts upon the work; and as it gradually uncoils and becomes weaker, on the contrary the lever of action becomes longer.
Having thus explained the nature and operation of the regulator, and of the maintaining power, we shall endeavour to describe the construction of an ordi nary watch, with the assistance of the annexed engravings. Fig. 1 represents the works, the upper plate being removed ; Pig. 2 is the upper plate, with the cock removed to show the balance ; and Pig. 3 a general elevation, supposed to be set out upon a straight line, in order to show the whole at one view. The same letters of reference are used to denote the seine parts in all the figures. a is the spring barrel ; b the chain attached by one end to the barrel, and after being wound several times round the barrel, hooked by the other end to the fusee c, mounted on pivots turning in holes in the two plates e e; one of these pivots f projects a considerable distance, and is cut square to receive a key, by turning which the fusee is turned round so as to wind the chain upon it, which causes the spring barrel to revolve also, and coils up the spring into a closer spiral than it was when at liberty; and upon the key being removed, the spring reacts upon the chain, and by that means turns the fusee. To prevent over winding, a guard is added, which consists of a small lever g, which, when the fusee has received a certain number of turns of the chain, presses against a stop h on the top of the fusee. k is the great wheel attached to the base of the fusee by a ratchet and click, by which means the fusee can be wound up with out turning the great wheel ; this latter has 48 teeth, and turns a pinion of 12 teeth on an arbor in the centre of the watch, which carries the minute-hand; upon this arbor is fixed the centre wheel m, of 54 teeth, working in a pinion fixed upon the arbor of the third wheel n, of 48 teeth, which turns the pinion of the contrate wheel o, of 48 teeth ; the contrate wheel gives motion to a pinion of 6 teeth, which is fixed upon the arbor of the crown or balance wheel p, which has 15 large teeth, that stop against two pallets alternately upon the verge or arbor of the balance g ; these pallets are two small teeth projecting from the verge at nearly right angles to each other, and constitute the escapemen4 the object of which, as in a clock, is to prevent the train run ning down rapidly by the action of the main spring, as would be the case if there were no check to it; but at each vibration of the balance, one of the pallets engages a tooth of the crown, thereby retarding the motion of the train, and imparting fresh impetus to the balance ; and no sooner has the pallet swung clear of the tooth, but the other pallet engages another tooth on the oppo site side of the wheel. One of the pivots of the balance works in a small frame r called the potence ; the lower pivot of the verge works in it also, and the upper pivot turns in a cock a screwed to the plate e. The minute-hand t is fixed upon the outer end of a tube which fits tight upon the arbor of the cen tral wheel, and which carries upon its inner end a pinion of teeth; this pinion turns a wheel v of 48 teeth, on whose arbor is a pinion of 16 teeth turning another wheel of 48 teeth, the arbor of which is a tube fitting upon the other tube on the central arbor, and carries the hour-hand z. The tension of the main spring is adjusted in the first instance by the maker, who turns its arbor, on the head of which is fixed a ratchet y, in which a click takes and thereby holds it fast when wound up to the proper pitch; subsequently, when a watch is perceived to gain or lose time, it is regulated by strengthening or weakening the pendulum spring 1, Fig. 2, which will cause it to move quicker or slower. This adjustment of the pendulum spring is effected thus : the spring is fixed to a stud 2 upon the plate e by one end, and to the verge of the balance by the other ; 3 is a lever lying betwixt the spring and the plate, and turning in a collar in the plate concentric with the centre of the balance, the verge of which passes through a hole in the lever; upon the lever is fixed a small stud 4 with a notch in it to receive the spring ; the acting part of the spring is from 4 to the centre, therefore by turning the lever in either direction, the length of the spring is altered, and in order to regulate this length with precision, the arc through which the end of the lever can be made to traverse on the plate, is divided into a number of equal parts or degrees. In Figs. 1 and 3 are shown four pillars, by which the two plates of a watch are held together ; and in Fig. 2, the heads of the same pillars are represented coming through the upper plate, with small pins put through them to keep the plate down.