Japanese Clock - The Problem of Varying Hour Lengths

The Problem of Varying Hour Lengths

Beginning in 1844 the calendar was revised to provide differing hour lengths for different parts of the year. Japanese clocks used various mechanisms to display the changing temporal hours. The most practical way was with a pillar clock, where the clock indicated time not on a clock face, but on an indicator attached to a weight that descended in a track. Movable time indicators ran alongside the track of the weight and its attached indicator. These indicators could be adjusted for the seasons to show the length of the day and nighttime hours. When the clock was wound, the indicator was moved back up the track to the appropriate marker. This setup had the advantage of being independent of the rate of the clock itself.

The use of clock faces was part of the European technology received in Japan, and a number of arrangements were made to display Japanese hours on clock faces. Some had movable hours around the rim of a 24 hour clock dial. Others had multiple clock faces that could be changed with the seasons. To make a striking clock that told Japanese time, clockmakers used a system that ran two balances, one slow and one fast. The appropriate escapement was changed automatically as the time moved from day to night. The myriad year clock designed in 1850 by Hisashige Tanaka uses this mechanism.

In 1873 the Japanese government adopted Western style timekeeping practices, including equal hours that do not vary with the seasons, and the Gregorian calendar.