Pillar clock, Japanese, 1800-1870.
© Science Museum / Science & Society Picture Library
Detail of mechanism. The 'pillar' clock is a type peculiar to Japan, in which the driving weight itself is the time indicator as it falls slowly past a scale of hours mounted below the time-keeping part of the movement. The hour numerals are adjustable by hand to allow for the varying hours of the day and night through the year. The Japanese system of 'temporal hours' timekeeping until 1870 divided the day and night each into six equal 'hours'. The length of these 'hours' differed throughout the year as the seasons changed.