Having seen the most essential parts of the repetition, there remains only one of which an idea must he given, and which we shall endeavour to make the reader under stand. This is the all or nothing, which has this property, that if the cord is not fully drawn, so as to make the arm b of the rack C press on the snail L, the hammer will not strike ; so that, by this ingenious mechanism, the piece ill repeat the exact hour; if otherwise, it will not repeat at all.
We have seen, that when the cord X is pulled, the pin wheel G, (Fig. I.), oversets the piece in, and makes it come to x; and that before the hammer can strike, a small spring must bring back. the piece in, to put it in holding with the pins ; after that, it is easy to see, that if, in place of alloil,g the piece in to take its situation, it were made to be still more overset, the repeating spring bring ing back the pin wheel, the hammer would not strike while this piece remained overset ; this is precisely the ef fect that the piece 'FR (Fig. 2.) produces, which is on that account called tile all or nothing piece. This is effected in the following manner : The piece in (Fig. 1.) carries a pin, which goes through the plate by the opening o, (Fig. 2.); if we pull the cord, the pin wheel causes the piece in to move, as we have just now seen. The pin which it car ries conies to press against the end o of the all or nothing piece, and sets it aside, so that the pin shall arrive at the extremity, which is a little inclined: But the spring d tend ing to bring back the arm o, the inclined plane obliges the pin to describe still a small space, which takes the arm m (PlateCCCV. Fig. 1.) entirely out of the reach of the pins, so that the hammer cannot strike, unit ss he pin is disengaged front the end of the arm o. To effect this, the arm of the rack must come and press on the snail L, which moves on a stud V, fixed to the all or nothing piece TH. Now, in pressing the snail, the arm o of the pin is set aside, which getting free, gives liberty to the at m in to present itself to the pins of the wheel G, and to the hammers that of striking the hours and quarters given by the dial work and hands.
The ratchet R (Fig. 3.) is that of the click and ratchet work of the movement ; c is the click. r the spring. The
ratchet R is put on a square of the barrel arbor ; this square being prolonged, serves to wind up the spring by means of a key ; B is the barrel in which the spring or motive force for the repetition must be put ; V is a screw, called the eccentric or pivot carrying piece : On the part which enters with force into the plate, a little out from the centre of the arbor of the. screw, a hole is made for the pivot of the anchor A. In making this screw turn, the pivot of the arbor of the anchor is made to go farther or nearer the centre, and consequently the anchor itself, so that the points of the pallets take more or less in, ac cording as is required with the teeth of the 'scapement wheel. A, Fig. 2. is the cock of the 'scapement, it carries the silk thread or spring, to which the pendulum is suspended. One of the ends of the silk thread is at tached to the arbor c, which is called avance or retard, (fast or slow) ; the other end of this' arbor goes through to the dial, and is squared, to receive a key. By this means, we can turn the arbor c to any side, so as to lengthen or shot ten the silk thread which serves to suspend the pendulum, Whose length is changed by this method.
The anchor A, Fig. 1, is fixed on an arbor similar to that for a second's pendulum. This arbor carries the fork T, which gives motion to the pendulum. The pivot which this arbor carries at the end where the fork is, enters into a hole made in the cock A, Fig. 2.
Fig. 4. represents in perspective the wheel D, whose revolution is performed in an hour ; it is the arbor of it that cart ics the wheel ni of Fig. 3. This wheel in is seen in perspective in Fig. 5. whose cannon serves to carry the minute hand. Fig. 6. represents in perspective the wheel S of Fig. 3. It is the arbor of this wheel prolonged, which passing to the motion work, carries the quarter snail It, Fig. 2. The pinion of this wheel S, pitches into the hour wheel, seen in perspective in Fig. 7 ; and it is on the socket of this wheel, that the hour hand is adjust ed or fixed.
It will be seen from the preceding description, that the pieces of the repeating motion work are here placed on the back of the pillar plate. Placing them on the fore plate will make no difference.