Horloge à une roue

Historical significance

• Built in La Chaux-de-Fonds by Samuel Roy and his three sons, this clock has only one wheel for the movement and one for the striking mechanism. Made without any pinions, it only needs to be wound every eight days and indicates the hours, minutes and seconds. A full strike sounds the hours at every quarter.
• The eleven-kilogram pendulum, with its steel and brass rods, the winding system and the striking mechanism under the main movement can all be seen through the three glazed sides of the walnut-veneered case.
• The large dial, which bears the clockmaker's signature as well as the inscription Non plus ultra, shows the hours and minutes with numbers painted in a spiral line. A single hand indicates both the hour and minute; as it follows the spiral line, its length automatically increases. When it gets to twelve o'clock, the hand shortens by dropping onto the XII below, and then starts round the spiral again.
• There is no need, therefore, for the usual gear-train of the motion work. The seconds hand moves from left to right for one minute, then back for the next one.
• The movement has only one wheel, functioning as both driving-wheel and escape wheel. It has ninety teeth and makes one revolution every three hours.

Sources & references

1. Musée international d'horlogerie, online collection record, inv. IV-541: https://collection.mih.ch/fr/collection/item/35183/

Where sources disagree, the disagreement is stated rather than resolved silently.