Motion work is the name given to the wheels and pinions used to make the hour hand go once around the dial while the minute hand goes twelve times. Here a few preliminary observations will do much toward clearing up the operations of the trains. The reader will recollect that we started at a fixed point in the time train, the center arbor which must revolve once per hour, and increased this motion by making the larger wheels drive the smaller (pinions) until we reached sixty or more revolutions of the escape wheel to one of the center arbor. This gearing to increase speed is called “gearing up” and in it the pinions are always driven by the wheels. In the case of the hour hand we have to obtain a slowing effect and we do so by making the smaller wheels (pinions) drive the larger ones. This is called “gearing back” and it is the only place in the clock where this method of gearing occurs.

We drew attention to a common usage in the gearing up of the time trains—that of making the relations of the wheels and pinions 8 to one and 7.5 to one; 7.5×8=60. So we find a like usage in our motion work, viz., 3 to one and 4 to one; 3×4=12. Say the cannon pinion has twelve teeth; then the minute wheel generally has 36, or three to one, and if the minute wheel pinion has 10, the hour wheel will have 40, or four to one. Of course, any numbers of wheels and pinions may be used to obtain the same result, so long as the teeth of the wheels multiplied together give a product which is twelve times that of the pinions multiplied together; but three and four to one have been settled upon, just as the usage in the train became fixed, and for the same reasons; that is, these proportions take up the least room and may be made with the least material. Also, the pinion with the greatest number of teeth, being the larger, is usually selected as the cannon pinion, as it gives more room to be bored out to receive the cannon, or pipe. If placed outside the clock plate, the minute wheel and pinion revolve on a stud in the clock plate; but if placed between the frames, they are mounted on arbors like the other wheels. The method of mounting is merely a matter of convenience in the arrangement of the train and is varied according to the amount of room in the movement, or convenience in assembling the movement at the factory, little attention being paid to other considerations.

The cannon pinion is loose on the center arbor and behind it is a spring, called the center spring, or “friction,” Figs. 89 and 90, which is a disc that is squared on the arbor at its center and presses at three points on its outer edge against the side of the cannon pinion; or it may be two or three coils of brass wire. This center spring thus produces friction enough on the cannon to drive it and the hour hand, while permitting the hands to be turned backward or forward without interfering with the train. In French mantel clocks the center spring is dispensed with and a portion of the pipe is thinned and pressed in so as to produce a friction between the pipe and the center arbor which is sufficient to drive the hands; this is similar to the friction of the cannon pinion in a watch.

In some old English house clocks with snail strike, the cannon pinion and minute wheel have the same number of teeth for convenience in letting off the striking work by means of the minute wheel, which thus turns once in an hour. Where this is the case the hour wheel and its pinion bear a proportion to each other of twelve to one; usually there is a pinion of six leaves engaging a wheel of 72 teeth, or seven and eighty-four are sometimes found.

In tower clocks, where the striking is not discharged by the motion work, the cannon pinion is tight on its arbor and the motion work is similar to that of watches. See Fig. 91.

The cannon pinion drives the minute wheel, which, together with its pinion, revolves loosely on a stud in the clock plate, or on an arbor between the frames. The meshing of the minute wheel and cannon pinion should be as deep as is consistent with perfect freedom, as should also that of the hour wheel and minute pinion in order to prevent the hour hand from having too much shake, as the minute wheel and pinion are loose on the stud and the hour wheel is loose on the cannon, so that a shallow depthing here will give considerable back lash, which is especially noticeable when winding.

The hour wheel has a short pipe and runs loosely on the cannon pinion in ordinary clocks. In quarter-strike cuckoos a different train is employed and the wheels for the hands are both on a long stud in the plate and both have pipes; the minute wheel has 32 teeth and carries four pins on its under side to let off the quarters. The hour wheel has 64 teeth and works close to the minute wheel, its pipe surrounding the minute wheel pipe, and held in position by a screw and nut on the minute pipe. A wheel of 48 and a pinion of 8 teeth are mounted on the sprocket arbor with a center spring for a friction, the wheel of 48 meshing with the minute wheel of 32 and the 8-leaf pinion with the hour wheel of 64. It will be recollected that the sprocket wheel takes the place of the barrel in this clock and there is no center arbor as it is commonly understood. The sprocket arbor in this case turns once in an hour and a half, hence it requires 48 teeth to drive the minute wheel of 32 once in an hour, as it turns one-third of a revolution (or 16 teeth) every half hour. The sprocket arbor, turning once in an hour and a half, makes eight revolutions in twelve hours and its pinion of eight leaves working in the hour wheel of 64 teeth turns the hour hand once in twelve hours.

In ordinary rack and snail striking work the snail is generally mounted on the pipe of the hour wheel, so that it will always agree with the position of the hour hand and the striking will thus be in harmony with the position of the hands.

Striking Trains.--It is only natural, after finding certain fixed relations in the calculations of time trains and motion work, that we should look for a similar point in striking trains, well assured that we shall find it here also. It is evident that the clock must strike the sum of the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 78 blows of the hammer, in striking from noon to midnight; this will be repeated from midnight to noon, making 156 blows in 24 hours, and if it is a 30-hour clock, six hours more must be added; blows for these will be 21 more, making a total of 177 blows of the hammer for a 30-hour strike train. The hammer is raised by pins set in the edge of a wheel, called the pin wheel, and as one pin must pass the hammer tail for every blow, it is evident that the number of pins in this wheel will govern the number of revolutions it must make for 177 blows, so that here is the base or starting point in our striking train. If there are 13 pins in the pin wheel, it must revolve 13.5 times for 177 blows; if there are 8 pins, then the wheel must revolve 22.125 times in giving 177 blows; consequently the pinions and wheels back to the spring or barrel must be arranged to give the proper number of revolutions of the pin wheel with a reasonable number of turns of the spring or weight cord, and it is generally desirable to give the same, or nearly the same, number of turns to both time and striking barrels.

If it is an eight-day clock the calculation is a little different. There are 156 blows every 24 hours; then as the majority of “eight-day” clocks are really calculated to keep time for seven and a half days, although they will run eight, we have: 156×7.5=1,070 blows in 7.5 days. With 13 pins we have 1,070÷13=80 and 4/13ths revolutions in the 7.5 days. If now we put an 8-leaf pinion on the pin wheel arbor and 84 teeth in the great wheel or barrel, we will get 10.5 turns of the pin wheel for every turn of the spring or barrel; consequently eight turns of the spring will be enough to run the clock for the required time, as such clocks are wound every seventh day.

Figuring forward from the pin wheel, we find that we shall have to lock our striking train after a stated number of blows of the hammer each hour; these periods increase by regular steps of one blow every hour, so that we must have our locking mechanism in position to act after the passage of each pin, whether it is then used or not; so the pinion that meshes with the pin wheel, and carries the locking plate or pin on its arbor must make one revolution every time it passes a pin. If this is a 6-leaf pinion, the pins on the pin wheel must therefore be 6 teeth apart; or an 8-leaf pinion must have the pins 8 teeth apart; and vice versa. For greater convenience in registering, the pins are set in a radial line with the spaces of the teeth in the pin wheel, as this allows us to measure from the center of the pinion leaf.

It will thus be seen that the calculation of an hour striking train is a simple matter; but if half hours are also to be struck from the train, it will change these calculations. For a 30-hour train 24 must be added to the 156 blows for 24 hours, 180 blows being required to strike hours and half hours for 24 hours. These blows may be provided for by more turns of the spring, or different numbers of the wheels and pinions, which would then also vary the spacing of the pins.

Half hours may also be struck directly from the center arbor, by putting an extra hammer tail on the hammer arbor, further back, where it will not interfere with the hammer tail for the pin wheel, and putting a cam on the center arbor to operate this second hammer tail. This simplifies the train, as it enables the use of a shorter spring or smaller wheels while providing a cheap and certain means of striking the half hours. Half-hour trains are frequently provided with a separate bell of different tone for the half hours, as with only one bell the clock strikes one blow at 12:30, 1 and 1:30, making the time a matter of doubt to one who listens without looking, as frequently happens in the night.

Fig. 92 shows an eight-day, Seth Thomas movement, which strikes the hours on a count wheel train and the half hours from the center arbor. All the wheels, pinions, arbors, pins, levers and hooks are correctly shown in proper position, but the front plate has been left off for greater clearness. The reader will therefore be required to remember that the escape wheel, pallets, crutch, pendulum and the stud for the pendulum suspension are really fixed to the front plate, while in the drawing they have no visible means of support, because the plate is left off.

The time train occupies the right-hand side of the movement and the striking train the left hand. Running up the right-hand from the spring to the escape wheel, we find an extra wheel and pinion which is provided to secure the eight days’ run. We also see that what would ordinarily be the center arbor is up in the right corner and does not carry the hands; further, the train is bent over at a right angle, in order to save space and get the escape wheel in the center at the top of the movement. The striking train is also crowded down out of a straight line, the locking cam being to the right of the pin wheel and the warning wheel and fly as close to the center as possible. This leaves some space between the pin wheel and the intermediate wheel of the time train and here we find our center arbor, driven from the intermediate wheel by an extra pinion on the minute wheel arbor, the minute wheel meshing with the cannon pinion on the center arbor. This rearranging of trains to save space is frequently done and often shows considerable ingenuity and skill; it also will many times serve to identify the maker of a movement when its origin is a matter of doubt and we need some material, so that the planting of trains is not only a matter of interest, but should be studied, as familiarity with the methods of various factories is frequently of service to the watchmaker.

Fig. 93 is the upper portion of the same striking train, drawn to a larger scale for the sake of clearness. It also shows the center arbor, both hammer tails and the stop on the hammer arbor, which strikes against the bottom of the front plate to prevent the hammer-spring from throwing the hammer out of reach of the pins. The pin wheel, R, and count wheel, E, are mounted close together and are about the same size, so that they are shown broken away for a part of their circumferences for greater clearness in explaining the action of the locking hook, C, and the locking cam, D.

Fig. 94 shows the same parts in the striking position, being shown as just about to strike the last blow of 12. Similar parts have similar letters in both figures.

The count wheel, E, is loose on a stud in the plate, concentric with the arbor of the pin wheel, R. The pivot of R runs through this stud. The sole office of the count wheel is to regulate the distance to which the locking hook C, is allowed to fall. The count hook, A, and the locking hook, C, are mounted on the same arbor, B, so that they move in unison. If A is allowed to fall into a deep slot of the count wheel, C will fall far enough to engage the locking face of the cam D and stop the train, as in Fig. 93. If, on the contrary, A drops on the rim of the wheel, C will be held out of the locking position as D comes around (see Fig. 94), and the train will keep on running. It will be seen that after passing the locking notch, D, Fig. 94, will in its turn raise the hook C, which will ride on the edge of D, and hold A clear of the count wheel until the locking notch of D is again reached, when a deep notch in the wheel will allow C to catch, as in Fig. 93, unless C is stopped by A falling on the rim of the wheel, as in Fig. 94.

One leaf, F, of the pinion of the locking arbor sticks out far enough to engage with the count wheel teeth and rotate the wheel one tooth for each revolution of D, so that F forms a one-leaf pinion similar to that of a rack striking train. Here we have our counting mechanism; F and D go around together; F moves E one tooth every revolution. A holds C out of action (Fig. 94) until A reaches a deep slot, when C stops the train by engaging D (Fig. 93).

The count wheel, E, must have friction enough on its stud so that it will stay where the pin F leaves it, when F goes out of action and thus it will be in the right position to suitably engage F on the next revolution. Too much friction of the count wheel on its stud will use too much power for F to move it and thus slow the train; if there is too little friction here the count wheel may get in such a position that F will get stalled on the top of a tooth and stop the train.

The count hook, A, must strike exactly in the middle of the deep slots, without touching the sides of the slots in entering or leaving, as to do this would shift the position of the count wheel if the rubbing were sufficient, or it might prevent A from falling (as A and C are both very light) and the clock would go on striking. If the hook A does not strike the middle of the spaces between the teeth of the count wheel, it will gradually encroach on a tooth and push the wheel forward or back, thus disarranging the count. Many a clock has struck 13 for 12 in this way because the hook was a little out. This did not occur in the smaller numbers because the action was not continued long enough to allow the hook to reach a tooth. The pin, F, should also mesh fairly and freely in the teeth of the count wheel, or a similar defect is likely to occur.

When repairing or making new count hooks, A, Figs. 93 and 94, they must be of such a length that they will enter the slots on a line radial with the center of the wheel. The proper length and direction are shown at A, Fig. 95, while B and C are wrong. With hooks like either B or C you can set or bend the hook to strike right at one and as you turn the clock ahead the hook does not fall in far enough and at twelve it only strikes eleven. Then if you bend the same hook to strike right at twelve it will strike two at one and as you turn the clock ahead it will strike right at about five or seven. A, Fig. 95, being of the proper length and shape will give no trouble. Many of the count wheels of the older clocks were divided by hand and are not as accurate as they should be; when a wheel of this kind is found and a new wheel cannot be substituted (because the clock is an antique and must have the original parts preserved) it will sometimes require nice management of the hook A to obtain correct striking. A little manipulation of the pinion, F, Fig. 93 is sometimes desirable also, if the count wheel is very bad.

The locking face of the cam, D, must also be on a line radial to its center, or it will either unlock too easily and go off on the slightest jar or movement of the clock, or the face will have too much draw and the hook C will not be unlocked when the clock is fully wound, and the spring pressure is greatest. In this case the clock will not strike when fully wound, but will do so when partly run down, and as the count wheel train strikes in rotation, without regard to the position of the hands, you will have irregular striking of a most puzzling sort. Repairs to this notch are sometimes required, when the corner has become rounded, and the best way to make them is to cut a new face on the cam with a sharp graver, being careful to keep the face radial with its center.

Because the count wheel strikes the hours in rotation, regardless of the position of the hands, if the hands are turned backwards past the figure 12 on the dial the striking will be thrown out of harmony with the hands. To remedy this the count hook, A, has an eye on its rear end and a wire, shown in Fig. 92, hangs down to where it can be reached with the hand when the dial is on. Pulling this wire will lift A and C and cause the clock to strike; by this means the clock may be struck around until the position of the striking train agrees with that of the hands. Where this wire is not present the striking is corrected by turning the hands back and forth between IX and XII until the proper hour is struck.

Now we come to the releasing mechanism, which causes the clock to strike at stated times. I, Figs. 93 and 94, is an arbor pivoted between the plates and carrying three levers, H, K and J, in different positions on the arbor. H is directly under the count hook, A, and lifts A and C whenever J is pushed far enough to one side by L on the center arbor, which revolves once an hour. Thus L, through J, H and A, C, unlocks the train once every hour. When C is thus lifted the train runs until the warning pin, O, Figs. 93 and 94, strikes against the lever K, which is on the same arbor with H and J. This preliminary run of the train makes a little noise and is called “warning,” as the noise notifies us that the train is in position to commence striking. The lever K and the warning pin, O, then hold the train until L has been carried out of action with J and released it, when O will push K out of its path at every revolution and the clock will strike.

The half hours are struck by L¹ pressing the short hammer tail, G¹, and thus raising and releasing the hammer once an hour.

In setting up the striking train after cleaning, place the pin wheel so that the hammer tail, G, may be about one-fourth of the distance from the next pin, as shown in Fig. 93; this allows the train to get well under way before meeting with any resistance and will insure its striking when nearly run down. If the hammer tail is too close to the pin, it might stop the train when there is but little power on.

Then place D in the locked position, with A in a deep slot of the count wheel and C in the notch of D. Next place the warning wheel with its pin, O, on the opposite side of its arbor from the lever K, see Fig. 93. This is done to make sure that when it is unlocked for “warning” the train will run far enough to get the corner of the lock, D, safely, past C, so that it will not allow C to fall into the notch again and lock the train when J, K and H are released by L. This is the rule followed in assembling these clocks at the factories and is simple, correct and easily understood. A study of these points in Fig. 93 will enable any one to set up a train correctly before putting the front plate on.

If the workman gets a clock that has been butchered by some one who did not understand it (and there are many such), he may find that when correctly set up the clock does not strike on the 60th minute of the hour; in such a case a little bending of J, in or out as the case may be, will usually remedy the trouble. The same thing may have to be done to the hammer tails, G and G¹, or the stop on the hammer arbor. If both hammer tails are out of position, bend the stop; if one is right, let the stop alone and bend the other tail.

A rough, set or gummy spring will cause irregular striking. In such a case the clock will strike part of the blows and then stop and finally go on again and complete the number. Much time has been lost in examining the teeth of wheels and pinions in such cases when the trouble lay in the spring. Too strong a spring will make the movement strike too fast; too weak a spring will make it strike slow, especially in the latter part of the day or week, when it has nearly run down.

Too small a fan, or a fan that is loose on its arbor, will allow the clock to strike too fast. If this fan is badly out of balance it will prevent the train from starting when there is but little power on.

There is a class of clocks which have the count wheel tight on the arbor, outside the clock plate. Many of them are on much tighter than they should be. In such a case take an alcohol lamp and heat the wheel evenly, especially around the hub; the brass will expand twice as much as the steel and the wheel may then be driven off without injury.

Fig. 96 shows another typical American eight-day train, made by the Gilbert Clock Company, and striking the half hours from the train. Here we notice, on comparing with Fig. 92, that there are many points of difference. First the notches on the count wheel are twice as wide as they are in Fig. 92. This means that half hours are struck on the train; this will be explained later. Next there are two complete sets of notches on the wheel, which shows that the wheel turns only once in twenty-four hours, whereas the other makes two revolutions in that time. There are no teeth on the count wheel, so that it must be fast to its arbor, which is that of the great wheel and spring, while Fig. 92 has a separate stud and it is loose. The wheel being on the spring arbor and going once in 24 hours, there must be one turn of spring for each 24 hours which the train runs. There is no pin wheel in Fig. 96, but instead of this two pins are cut out of the locking cam to raise the hammer tail as they pass. There are also two locking notches in the locking cam. The cams on the center arbor are stamped out of brass sheet, while those of Fig. 92 were of wire.

Turning to the enlarged view in Fig. 97 and comparing it with Fig. 93, we find further differences. The levers K and J are here made of one piece of brass, while the others were separate and of wire. The lifting lever, H, is flattened at its outer end in Fig. 93, while in Fig. 97 it is bent at right angles and passed under the count hook, A. The hook, C, Fig. 97, is added to the arbor, B, as a safety device, in case the locking hook should fail to enter its slot in the cam, D. It is shown as having just stopped the warning pin in Fig. 96. There is but one hammer tail, G, and the hammer stop acts against the stud for the hammer-spring, instead of against the bottom of the front plate, as in Fig. 92.

The first important difference here is in the position of the count hook, A. In Figs. 92 and 93 the hook must be exactly in the middle of the slot, or there will be trouble. In trains striking half hours from the train, we must never allow the hook to occupy the middle of the slot, or we will have more trouble than we ever dreamed of. In this instance the count hook must enter the slot close to (but not touching) the side of the slot when the clock stops striking; then when the half hour is struck the count wheel will move a little and the hook must drop back into the same slot without touching; this brings it close to the opposite side of the same slot and the next movement will land the hook safely on top of the wheel for the strokes of the hour. Fig. 96 shows its position after striking the half hour and ready to strike the hour of two. Fig. 97 shows it dropping back after striking two.

In setting up this train, see that the count hook. A, goes into the slot of the count wheel close to, but not touching, one side of the slot in the count wheel, and, after placing the intermediate, insert the locking cam, D, so that it engages the locking hook; then put in the warning wheel with the warning pin, O, safely to the left of the hook C, Fig. 97, so that it cannot get past that hook after striking. Placing the wheel with its warning pin six or eight teeth to the left of the edge of the bottom plate is generally about right. The action of the levers, H, J, K, the hammer tail, G, and the cam, L, in striking the hours is the same as that already described in detail for Figs. 93 and 94, hence need not be repeated here. L¹ strikes the half hours by being enough shorter than L to raise the hooks for one revolution, but not quite so high as for the hours. The cams L, L¹ are friction-tight on the center arbor and may be shifted on the arbor to register the striking on the 60th minute, if desired. When the hands and strike do not agree, turn the minute hand back and forward between IX and XII, thus striking the clock around until it agrees with the hands.

Sometimes, if the warning pin is not far enough away, an eight-day clock will strike all right for a number of days and then commence to gain or lose on the striking side. It either does not strike at some hours, or half hours, or it may strike sometimes both hour and half hour before stopping. Take the movement out of the case and put the hands on; then move the minute hand around slowly until the clock warns. Look carefully and be sure there is no danger of the clock striking when it warns. If this looks secure, then move the hand to the hour, making it strike; say it is going to strike 9 o’clock; when it has struck eight times, stop the train with your finger and let the wheels run very slow while striking the last one, and when the rod drops into the last notch stop the train again and hold it there.

For the striking part to be correct, the warning pin on the wheel wants to be about one-fourth of a revolution away from the rod when the clock has struck the last time, or as soon as this rod falls down far enough to catch the pin. The object of this is so there is no chance of the warning pin getting past the rod at the last stroke; this it is liable to do if the pin is too close to the rod when the rod drops. If you will examine the clock as above, not only when it strikes IX, but all the hours from I to XII, you will generally find the fault. Of course, if the pin is too close to the rod when the rod drops, you must lift the plates apart and change the wheel so that the warning pin and the rod will be as explained.

Ship’s Bell Striking Work.--Of all the count wheel striking work which comes to the watchmaker, the ship’s bell is most apt to give him trouble. This generally arises from ignorance as to what the system of bells on shipboard consists of and how they should be struck. If he goes to some nautical friend, he hears of long and short “watches” or “full watches” and “dog watches.” If he insists on details, he gets the information that a “watch” is not a horological mechanism, but a period of duty for a part of the crew. Then he is told of the “morning watch,” “first dog watch,” “afternoon watch,” “second dog watch,” “off watch,” “on watch,” etc. Now the ship’s bell clock does not agree with these “watches” and was never intended to do so. As a matter of fact, it is simply a clock striking half hours from one to eight and then repeating through the twenty-four hours.

The striking is peculiarly timed and is an imitation of the method in which the hours are struck on the bell of the ship. As this bell is also used for other purposes, such as tolling in fogs, fire alarms, church services, etc., it will readily be seen that a different method of striking for each purpose is desirable to avoid misunderstanding of signals.

The method of striking for time is to give the blows in couples, with a short interval between the strokes of the couples and three times that interval between the couples. Odd strokes are treated as a portion of the next couple and separated accordingly, thus:

After striking eight bells the clock repeats, although the ship’s bell is generally struck in accordance with the two dog watches (which are of two hours’ duration each) before commencing the evening watch (8 to 12 p. m.). It will thus be seen that the clock should strike eight at 12 m., 4 p. m., 8 p. m., 12 p. m., 4 a. m., and 8 a. m.

In order to strike the blows in pairs two hammers are necessary, see Fig. 98; these hammers are placed close together, but not in the same plane. The pin wheel has twenty pins, see Figs. 98, 99, 100; some of these pins are shorter than the others, so that they do not operate one of the hammer tails. These are shown graphically in Fig. 100; where the two oblong marks at figure 1 represent the tops of the hammer tails shown in Fig. 99. It will be seen by studying Fig. 100 that with the wheel moving from left to right, the inside hammer tail will be operated for one blow, while the outer hammer tail will not be operated at all, thus giving but one blow, or “bell.” At the next movement of the pin wheel, the outside hammer will be operated by the long pin and the inside hammer by the short pin, thus giving one blow of each hammer, or “two bells.”

We now have these hammer tails advanced along the wheel so that the outside one is opposite the figure 3 in the drawing, while the other is opposite the figure 2, with one pin between them. The next movement of the pin wheel advances them so that the outside hammer will pass the next short pin and consequently that hammer will miss one blow and the pair will therefore strike three—one by the outside hammer and two by the inside. It thus goes on until the cycle is completed, eight blows being struck with the last four pins. The striking in pairs is effected by having the two hammer tails close together, so that the pins will operate both hammer tails quickly and there will then be an interval of time while the wheel brings forward the next pins. This is so spaced that the interval between pairs is three times that between the blows of a pair and the hammer tails should not be bent out of this position, or if found so they should immediately be restored to it. Tolling the bells, instead of striking them properly, is very bad form at sea and generally leads to punishment if persisted in, so that the jeweler will readily perceive that his marine customers are very particular on this point, and he should go any length to obtain the proper intervals in striking.

The pin wheel moves forward one pin for each couple of blows or parts of a couple, the odd blows being secured by the failure of the blow when the hammer tail passes the short pin. Thus it moves as far for one bell as for two bells; as far for three bells as for four, etc. The result is that the count wheel has no odd numbers on it, but instead two 2’s, two 4’s, two 6’s and two 8’s; the first two are counted on the count wheel, but only one is struck on the pin wheel, owing to the short pin; this is repeated at three, five and seven, when four, six and eight are counted on the wheel, but the last blow fails of delivery, owing to the short pin in the pin wheel at these positions.

The center arbor carries two pins, L and L¹, to unlock the train through the lever J, as it is really a half hour striking clock. The count hook, A; locking hook, C; count wheel, E; pins, P, and other parts have similar letters for similar parts as in the preceding figures and need not be further explained, as the mechanism is otherwise similar to the Seth Thomas movement shown in Fig. 92.