Modern time-reckoning in equal hours was not introduced into Japan until 1870. Before this time, Japan used a 'temporal hours' system, similar to that of Europe's in the middle ages, the period of dawn to dusk being divided into six equal hours and the period of darknes also into six equal hours. A daylight hour was in general of different length from a night hour and both varied according to season. This clock has adjustable numerals to allow for these variations. Timekeeping is controlled by a wheel balance with a balance spring, through a verge escapement, and striking is released by pins projecting from behind each of the numerals.
© Science Museum / Science & Society Picture Library