It must now be shown by what means the course which the pin wheel takes is regulated on the cord being pulled, and how it is proportioned to the hour which the hands point to on the dial.
A wheel S, or minute wheel, of the dial work, Fig. 3. has its arbor prolonged, and outside of the back of the pil lar plate. (In this case, and in common, the repeating work is put between the dial and foreplate of the frame.” It carries the piece sh, Fig. 2. the pin of which c turns the star wheel E, which takes twelve hours to go once round, and carries with it a piece L, called the hour snail, divided into twelve parts tending to the centre of the star wheel. Each of these parts forms different depths, like as many steps, which gradually come nearer the centre, and which serve to regulate the number of the hours which the hammer must strike. For this purpose the pulley P carries a pinion a, which pitches in with a portion of a wheel C, Fig. 2. called the rack. When the cord is pull ed, and the rack is in consequence made to advance to wards the snail, the arm b stops on such a step of the snail as it may meet with in its course ; and, according to the depth of this step, the hammer strikes a greater or less number of blows. It will strike only one hour if the arm 1; of the rack is stopped on the step 1, the most distant one from the centre, as then the pin wheel getting only one of its pins engaged, the hammer strikes only one blow. If, on the contrary, the step 12, which is the deepest and nearest the centre, is met by the arm b in its course, which cannot get there until the pin wheel shall have made one turn, then the spring in the barrel bringing it back, will cause the hammer to give 12 blows.
It remains to be seen how the quarters are repeated. The piece s, Plate CCCV. Fig. 2.which turns the star wheel, and takes one hour to make a revolution, is carried by anothor snail /1 (called the quarter snail,) formed by four divisions, making three paths or steps, on one of which, when the cord is pulled, the arm Q of a piece QD, called the finger, places itself, and according as the step is nearer or farther from the centre of the snail, the end D of the finger finds itself more or less aside from the centre a of the pulley P ; so that when the pull of the cord is finished, and the pulley returns by the force of the spring in the bar rel, one of its four pins acts on this finger, namely, the one which it finds at a distance from the centre a, which an swers to the elevation of the arm D, and this is-what de termines the blows for the quarters : thus when the finger is applied on the pin nearest the centre of the pulley, the hour hammer strikes only the number of hours that the snail L and the arm b of the rack have determined. If
the finger is placed on the second pin, it dots not stop the pulley till after the hour hammer has struck the hour, then a quarter, and so on.for the three quarters. Having thus given an idea of the essential parts of a repeater, let us DOW proceed to a particular description of a complete re peating clock with an anchor 'scapement.
Plate CCCV. Figs. 1, 2, and 3. represent all the parts of a repeating clock, seen in plan. Fig. 1. represents the wheel and pieces contained within the frame, or vv at are put between the two plates, with the exception bf the anchor A, which is placed in this way, to show the 'scape ment.
The wheels B, C, D, E, F, are those of the movement.
B is the barrel, which contains the clock mainspring. The great wheel is fixed to the bottom of the barrel B, and pitches into the pinion of the wheel C, which is the great intermediate wheel. D is the third, or the centre or minute wheel.* E the fourth wheel, or that where the contrite wheel was usually placed. F the ratchet, or 'scapement wheel. The centre wheel 1) makes a revolution in an hour. The pinion on which this wheel is fixed has its pivot prolonged, which passes through the fore plate, Fig. 3. This arbor or pivot, Fig. 4. enters spring tight into the cannon of the minute pipe wheel in, seen in perspec tive, Fig. 5. which makes also, by this means, a turn in an hour. This cannon carries the minute hand ; and its wheel m pitches into the returning or minute wheel S, .of the same number of teeth, and of the same diameter as the wheel in. The pinion of the wheel S makes twelve re volutions in the time that the hour wheel C makes one. The wheel C, which is one of the dial wheels, takes then 12 hours to make one revolution, and is that which carries the hour hand.