Strike. Name given by clockmakers to the part of a clock that rings the hours, the halves or the quarters. It is not known when the strike was invented; it is certain that it was used in the oldest mechanical clocks; it may be that it was invented earlier. What is stated in the article Clock concerning the one sent to Charlemagne shows that it had a kind of strike , since there were bronze balls that beat regularly every hour, on a little drum of the same metal, the same number of strokes as the hour shown by the clock.

Since all these strikes are built on approximately the same principles, we shall describe the one in a fifteen-day spring-driven clock; this strike is most commonly used, and once its action has been seen, all the others will be readily understood.

Spring-driven clock striking the hour and half-hour. See [Plate III, Figure 8], Q, P, O, M, N, L, showing a strike movement from the front. Q is the barrel with teeth around its circumference; there are 84 teeth. The barrel meshes with pinion P, 14 leaves, of the second wheel, 72 teeth; and the latter with the pinion of the third or pin wheel, S [O]; this wheel has 10 pins and 60 teeth. It drives the 6-leaf pinion of the stop wheel, which drives wheel N, also with a stop pin; finally the latter engages the pinion of fan L. The latter pinions usually have 6 leaves, but the wheels are indefinite; the numbers must not be so great as to make the teeth too fine, and the fan must turn fast enough to slow the movement. As to the second wheel, pin wheel and stop wheel, their numbers are defined. The latter must make one revolution for each hammer stroke, and the pin wheel must make 9 revolutions for one of the second wheel, which carries the count plate.

Thus we see that if the second wheel has 72 teeth, the pinion of the pin wheel has 8 leaves; if the latter wheel has 60, the pinion of the stop wheel has 6.

Another Figure [9] shows this movement in side view. P f is the detent, which is shown more clearly elsewhere; part F enters the notches in the count plate, which we shall discuss later, and part p stops the strike by blocking pin m of the stop wheel.

Part E, not clearly seen in the side view, is shown in another Figure [7], representing the clock from the front, with the dial removed. Part E presses on lifter D c B, with a part H shown below [Figure 14], marked h in the side view. Part C b releases the strike train, and part h releases the strike exactly on the hour. Hammer AY pivots at each end; it has a pallet at Y that extends inside the plate and is pushed by the pins on wheel o o , causing it to strike. We shall show how all these parts act 1) to make the clock strike, and 2) to do so accurately.

Assuming the spring in the barrel tends to turn it from Q towards W, clearly if the movement were free, it would turn; with wheel O turning from O to P, its pins would trip the hammer and cause it to strike the bell. But assuming stop m in the side view encounters part P of the detent, the movement can no longer turn. Now if the stop is released by moving the detent aside, once the movement is released, clearly the clock will strike. Here is how that is done. The lifter arm extends in front of the minute wheel, B. This wheel has two pins opposite each other and positioned so that when the minute hand shows 25 or 55 minutes, they start raising the arm. With the hand in one of these two positions, clearly as the lifter is raised, it will raise part E of the detent at the same time, and consequently release part PD e from pin m in the side view; thus, since the movement is free, the clock would strike. However, at the same instant part h of the lifter stops pin k set on wheel n , so the movement is stopped once again; therefore the clock cannot strike until as a consequence of the motion of the minute wheel, the lifter is no longer held up by the pin on the wheel; it drops and releases pin h , allowing the movement to turn and the clock to strike.

Now here is how it is made always to strike the same number of blows as the hour shown by the hands.

We said above that the detent has a part, F, that enters the notches in the count plate, which is shown in another Figure [13]. The plate fits the squared end of the second-wheel arbor, which extends through the back plate of the movement. Its diameter is such that when part f of the detent rests on the circumference, the other part, p , is too far from the stop pin on wheel m to encounter it. The notches, on the other hand, are deep enough so that when part f rests in one, part p encounters the stop pin on wheel m ; in the latter case, the clock can only strike once because, as we have said, the stop wheel makes one revolution for each hammer stroke. When the pin is released for an instant from part p , if the wheel can complete its rotation, the clock will strike, but only once. It may readily be deduced from this that as long as the detent rests on the circumference of the count plate, the clock will strike, but when f rests in the notches, it can only strike once, and only when part p of the detent has released the pin on the stop wheel.

Since wheel OO has ten pins, one of its revolutions represents ten strokes of the hammer. Furthermore, since this wheel, as we have said, makes nine revolutions for one of the second wheel, it follows that the pins will lift the hammer 90 times for one revolution of that wheel, and therefore of the count plate, which is mounted on its arbor. So if we assume that the detent always rests on the circumference of the plate, the clock will strike 90 times in one revolution, and with each stroke the plate will make 1/90th [1] of its revolution. Upon reflection, we see that 90 equals 12 plus the sum of the numbers from 1 through 12. Therefore the circumference of the count plate may be divided into 12 parts, as shown in a Figure [13], each one of which contains 1/90, 2/90, 3/90, etc., through 11/90; in addition, between the parts a further interval of 1/90 is left; as long as the detent rests on one of these parts, like 10, 11, 12, etc., the clock will strike 10, 11, or 12 times. Now 90 equals the number of times a clock must strike in 12 hours, since the number consists of 12 half-hours plus 78, the sum of the hours from 1 through 12. Therefore, since the count plate makes one revolution in 12 hours, it will cause the clock to strike the requisite number of times. Thus, assuming the detent rests in one of the notches, 10 for example, and the minute hand stands at noon, the strike , as we have explained, will start, and the clock will strike 11 times or 11 o'clock, after which the detent will drop into notch 11. At the half-hour, the strike will run again but give only one stroke, as we have said. Again, assuming that the detent rests on part 3 of the plate, the hour hand at 4 o'clock, and the minute hand at noon, the clock will strike 4 o'clock; if it keeps going till the half-hour, it will strike once, at 5 o'clock 5 times, and so forth.

We have said that the count plate is divided into 12 parts, but unlike the others the part assigned to one o'clock is included in the notch between 1 and 12. Since only one stroke is required for one o'clock, it is analogous to a half-hour. The notches in the plate, see Figure [13], are slightly wider than 1/90 of the circumference, because they must accommodate part f of the detent, but that makes no difference, since the part rests longer on the circumference of the plate in proportion to its thickness. To make the hour strike easier, the leading side of the notch is filed at an angle, as at A in Figure [13], to raise the detent more easily; once the first stroke has been given, the detent rests on the circumference of the plate, and the clock strikes the remaining times required.

It will readily be seen that the action of a strike may be achieved by a great variety of means, but since the ones we have described are the simplest, horologists use no others. Therefore one can be sure that every strike contains a driving force to operate the hammer, a count plate or its equivalent to determine the strokes, and two detents, the action of which is about the same as the one we have just described, and which determine the exact instant when the clock is to strike. The fan and its pinion slow the rate of the movement, to give a clear interval between the strokes. It is for this reason that in all kinds of strikes and repeaters the train must always have a certain number of wheels, to give the fan enough speed to be effective.

As for calculating the numbers for a strike train, in theory it is very simple. The only requirements are 1) that the pin wheel make such a number of revolutions in relation to the count plate that whatever the number of pins with which the clock strikes the hour and half-hour, it makes 90 hammer strokes for each revolution of the plate; or if it only strikes the hour, it only makes 78; this is plain from what we have said previously. 2) The stop wheel must make one revolution for each hammer stroke. If this wheel is fitted with two half-rings or -hoops, it only makes a half-revolution. Finally, since the plate must make two revolutions per day, its revolutions must always be twice the number of days the clock will go on a winding, and in this way the number of its revolutions relative to the spring barrel or the great wheel of the strike are determined. We shall illustrate this by an example. We have seen that the barrel of this strike has 84 teeth, and that it engages the 14-leaf pinion of the second wheel. Consequently the count plate, mounted on the arbor of this wheel, will make 6 revolutions for one of the barrel; but since this clock goes 18 days, the plate must make 36 revolutions in this period of time, and consequently the barrel 6, since one of its revolutions equals 6 of the plate. Thus we see how the revolutions of the count plate determine those of the spring barrel or the great wheel. See Clock, Spring-driven clock, Calculation, Numbers, etc.

The strike we have just explained is the one generally used in clocks, but since we have seen that all strikes are made about the same, those of striking watches are analogous, differing only in size. Since they are almost never used today, it is pointless to dwell on them, especially since anyone who has understood the strike mechanism of clocks will easily grasp that of watches.

1. The text gives 1/50th (translator's note).