3 : on the end of the arbor of the centre wheel 64 a tube is fitted, so as to go round with it by friction ; this carries the minute hand, but if the clock should require correction, the hand may be slipped round without moving the wheels ; this tube has a pinion of 40 teeth on its lower end, indicated by a dotted circle ; this turns another wheel 40, of 40 teeth, which has a pinion of six teeth on its arbor, turning a wheel 72, of 72 Teeth ; the two wheels 40 will both turn in an hour ; and 72 in 12 hours : the arbor of this wheel has the hour-h.nd, and is a tube going over the arbor of the minute-hand, so that the two hands are concentric. The barrel a is fitted to an imbor coming through the plate of the clock, and is filed square, to put on a key to wind up the weight ; the great wheel 96 is not fixed fast to the arbor, but has a click on it, which takes the teeth of a ratchet wheel cut upon the barrel ; so that the barrel may be turned in the di rection to wind up the weight without the wheel : but by the descent of the weight, the wheels will be turned by the click.
Having now described the going part of the clock, it remains to describe the me chanism by which the hours are struck. 78, fig. 2, is a great wheel of 78 teeth, with a barrel and click the same as 96 ; it turns a pinion of eight ; 64 is a wheel on the same arborturning a pinion of eight on the arbor of the wheel o of 48 ; th:s turns another pinion of eight, and wheel p of 48, which turns a pinion of six, on the same arbor with a thin vane of metal, which is called the fly, and by the resist ance of the air to its motion regulates the velocity of the wheels. The wheel 64 has eight pins projecting from it; these raise the tail a of the hammer, as they revolve ; the hammer is returned vio lently, when the pins leave its tail, by a spring in pressing on the end of a pin put through its art or, and strikes the bell, (the hammer and bell are behind the plate, and therefore unseen,) / is a short spring, which the other end of the pin through the arbor touches just before the hammer strikes the bell ; its use is to lift the hammer of the bell the instant it has struck, that it may not stop the sound. The eighth pin in the wheel 64 must pass by the hammer tail 78 times in striking the 12 hours, 1 + 2 + 3 + +5 + 6 + 7+ 8 + 9 +10 + 11 4 12 = 73, and as its pinion has eight leaves, each leaf of the pinion answers to a pin in the wheel 64; now as the great wheel has 78 teeth, it wjll turn once in 12 hours, the same as the other great wheel 96. In the wheel 64 eight of its teeth correspond to one of the pins for the hammer, and as the pinion of the wheel o has eight teeth, it (wheel o) will turn once for each stroke of the hammer. By the remaining wheels, one, o, multiply ing six, and the other, p, eight times, the fly will turn 6 X 8 = 48 times for one turn of o = one stroke of the hammer. Fig. 3. is also mechanism relating to the striking part : r is a small pinion of one tooth, called the gathering pallet, on the arbor of wheel o, and consequently turns once for each stroke of the hammer ; s is a segment of a large wheel which it turns (called the rack) ; t is an arm attached to the rack, whose end rests against a spiral plate V, called the snail; this is fixed on the tubular arbor before describ ed of the hour hand and wheel 72, and turns round with it once in 12 hours. The plate is divided into 12 equal angles, 30 degrees each, acid as it turns, each of these answers to an hour ; the circular arcs forming the circumference of the snail are struck from the centre of the arbor between each division with a differ ent radius, decreasing a certain quantity each time in the order of the hours. The circular part of the rack s is cut into teeth, each of which is of such a length, that every step upon the snail shall an swer to one of them ; so is a spring press ing against the tail of the rack, and act ing to throw the arm of the rack against the snail; g is a click, called the hawk's bill, taking into the teeth of the rack, and holding it up in opposition to the spring To : i k is a three-armed detent, called the warning piece ; the arm k is bent at its end, and passes through a hole in the front plate of the clock, so as to catch a pin placed in one of the arms of the wheel p, fig. 2, and which de
scribes the dotted circle in fig. 3 ; the other arm i stands so as to fall in the way of a pin in the wheel 40. In the present position of the figure, the wheels of the striking train are in motion, and would continue turning until the gather ing pallet r, which turns once at each stroke of the hammer, by its tooth lifts the rack s in opposition to the spring so one tooth each turn ; and the hawk's bill g retains the rack, until a pin in the end of the rack is brought in the way of the lever of the gathering pallet r, and stops the wheels from turning any further : it is in this position with the rack wound up, till its pin arrestsrthe tail r, that we shall begin to describe the operation of the striking of the clock The wheel 40, as we have said before, turns once in an hour, and consequently at the expiration of every hour the pin in it takes the end I, and moves it towards the spring near it ; this depresses the end k until it falls in the circle of the motion of the pin in the wheel p, fig. 2, at the same time the short tail depresses one end of the hawk's bill, and raises the other sr, so as to clear the teeth of the rack a ; immediately the spring Iv throws the rack back, until the end of its tail t touches that part of the snail which is nearest it ; when the rack falls back, the pin in it is moved clear of the gathering pallet r, and the wheels set at liberty; the maintaining power puts them in motion ; but in a very short time before the hammer has struck, the pin in the wheel p falls against the end of k, and stops the whole ; this operation happens a few minutes before the clock strikes, and this noise of the wheels turning is called the warning : when the hour is ex pired, the wheel 40 has turned so far as to allow the end of i to slip over its pin, as in the figure ; the small spring press ing against it raises the end k so as to be within the circle or the pin in the wheel p, fig. 2 : every obstacle is now removed, and the wheels run on the pinion ; the wheel 64 raises the hammer r, and it strikes on the bell, the gathering pallet r takes up the rack, a tooth at each turn, the hawk's bill g retaining it until the pin in the rack comes under the gather ing pallet r, and stops the motion of the whole machine, till the pin in the wheel 40 at the next hour takes the warning piece i k, and repeats the operation we have now described. As the gathering pallet turns once for each blow of the hammer, and its tooth gathers up one tooth of the rack at each turn, it is evi dent the number of teeth the rack is al lowed to fall back limits the number of strokes the hammer will make. This is done by the rack's tail t resting on the snail ; each step of the snail answers to one tooth of the rack, and one stroke of the hammer ; at each hour a fresh step of the snail is turned to the tail of the rack, and by this means the number of strokes is made to increase one at each time from one to twelve.
CLoor-work, in the limited meaning of the word used by artists, denotes only the machinery employed in the striking part of a clock ; that used for giving mo tion to the hands being called watch work. In its more extensive sense, it is generally understood to mean any combi nation of wheel-work, for any purpose, whose parts do not much exceed in size those of a common clock.