To produce the number of blows corresponding to the hour indicated on the dial is the purpose of the locking-plate or "count-wheel" (fig. 2), which has on its circumference indentations corresponding in number to the twelve hours on the dial. The locking-plate is so fastened to the clock frame that when the train is moving a pinion fastened to the arbor of wheel C revolves the plate. A rigid arm on the bearing f of the lever J rests in an indentation of the locking-plate; if now the train is set going, the arm will be raised out of the indentation of the revolving locking-plate; after the locking-cam a' has made one revolution, the arm rests on the blank circumference of the locking-plate and keeps the locking-lever f in a raised position until the locking-plate has revolved far enough to allow the arm to fall into another indentation of the locking-plate, which movement allows the locking-lever to sink into the notch of the locking cam. It is obvious that the spaces between the indentations of the lock ing-plate must be so arranged as to correspond to the number of hammer blows required to indicate the hour shown by the hands of the dial. One of the indentations has double the width of any other. This indentation is for the first hour, which requires but one blow, after which the train stops.
Repeating great disadvantage of the locking-plate striking-works is that if accidentally the clock strikes at any time between hours, the number of blows will no longer correspond to the time indicated on the dial. This disadvantage is obviated by the repeating striking-clock (pl. 125, .fig• 3). The counting-wheel above described is replaced by the " hour-snail " C, which has on its spirally-curved circumference steps cor responding in number to the twelve hours on the dial. The rack D is a segment of a ratchet-wheel movable at In, and has an arm r which, under. the pressure of a spring o, falls against the hour-snail C, and the clock is then ready to strike. At each revolution the short arm of the gathering pal let F, which revolves once at every blow of the hammer, catches into and moves one tooth of the rack D. The rack-hook E prevents the rack from falling back when the gathering pallet leaves a tooth. The gathering pal let continues to move the teeth of the rack, one after another, until the rack-hook E reaches the last tooth of the rack; then the longer piece, the "tail," of the gathering pallet will be intercepted by the pin a of the rack, and this pin will bring the train (not indicated in the Figure) to a stop. When the clock begins to strike the hour, the arm r rests against a step of the snail C, which step corresponds to the hour of the dial; the gathering pallet F, before it is stopped by the pin a, makes one revolution for each blow of the hammer. For example, at the sixth hour the pallet will make six revolutions and the clock will strike six. The tail of the gathering pallet remains at the pin a until a few minutes before the com pletion of the next hour; then the lifting piece G is raised by the pin of wheel H, which makes one revolution every hour. The lifting-pin G raises the rack-book E and releases the rack D, whose arm (r) again drops against the hour-snail C. The lifting-piece G has on the end of its upper arm a projection extending through the opening b of the clock fraine; as soon as the rack-hook is lifted out of the rack, the pin of the pin-wheel D (fig. 1) rests against this projection, and there remains until the lower arm of the lifting-piece G (fig. 3) has left the lifting-pin of the wheel H. The lifting-piece then drops, the pin-wheel is set free, and the striking process already described is repeated. This time, however, the clock will strike seven, the hour-snail having been moved one step further after striking the sixth hour. A lever J, bearing against the under side
of the lifting-piece G, has attached to its outer end a cord s, which, if pulled, raises the lifting-piece, and the clock strikes the hour just passed and repeats it any time, since the hour-snail retains its position up to the beginning of a new hour. This feature becomes useful at night when the time cannot be seen, as by pulling the string the hour last struck can be ascertained by the striking of the clock.
The Strasburg Cathedral Clock (pl. 124, fig. 6), an admirable produc tion of the clock-maker's skill, was constructed (1838-1840) by Schwilgue to replace a similar older work: it consists of three turret-like parts, of which the central one is 46 feet high. The part to the right in the Figure is circular, and contains winding stairs for reaching the various stories of the central or main turret. In front of the base, in the centre, stands a large celestial globe which illustrates one hundred and ten of the constel lations whose stars can be seen in the sky with the naked eye. This globe rotates in unison with the rotation of the starry firmament. On the base and behind this globe is a large rotating calendar-disc which indicates the movable feasts of each year, and, as the calendar rotates, Apollo, who stands beside it, points with a small rod to the existing day. In the centre of this calendar-disc, which is nine feet in diameter, is a smaller disc which indicates the rising and the setting of the sun, the course and phases of the moon, and the appearance of the eclipses of the sun and moon. On both sides of the calendar arc mechanical arrangements indicating the year, the cycle of the sun, the golden number, the Roman indiction, the epacts, and Easter for the current year. Above the calendar, on a projection of the base, seven chariots slowly pass by in the course of a week—Sunday, Apollo with the horses of the sun; Monday, Diana with a stag; Tuesday, Mars with war-horses (chargers); Wednesday, Mercury with lynxes; Thursday, Jupiter with thunderbolt and clouds; Friday, Venus with doves; and Saturday, Saturn with a chimera. The base next carries the " lion gallery," so called from two lions, one of which holds in its claws the escutcheon of the city of Strasburg and the other a helmet. In the centre of this gallery is the clock dial-plate which indicates the time. Beside the clock stand two genii, one of whom strikes the quarter hours upon a bell, and the other hourly turns an hour-glass. The lower division of the central turret contains an orrery, upon which are represented the annual movements of the planets Mercury, Venus, Earth, Mars, Jupiter, and Saturn. In the division next above the clock, on a starry firmament, the gradual waxing and waning of the moon is illustrated by means of the rotation of a ball, one-half of which is white and the other half black. In the succeeding higher division is an effigy of Death holding in one hand a scythe and In the other hand a bone. On each side of this figure is placed a bell: at the time of the quarter hour the figure of a child enters a side door, and, turning to one of the bells, strikes once upon it with a rod, and then disappears through another side-door; at the time of two quarters, or half hour, a youth (huntsman) appears in the same manner and strikes twice with an arrow upon the bell; three-quarters of the hour are indicated by a man (warrior), who strikes thrice upon the bell with a sword; and finally, at the fourth quarter, or full hour, an old man emerges from the side-door and strikes the bell with his crutch, whereupon the arm of " Death " is raised and slowly strikes the hour upon the larger of the two bells.