Japanese clock (和時計)
A Japanese clock is a clock made in Japan mainly during the Edo period.
A mechanical clock was first brought to Japan in 1551 when Francis XAVIER presented it to Yoshitaka OUCHI.
It seems that domestic production of the mechanical clock was promoted since then.
In 1605, TSUDA Sukezaemon Masayuki presented a jimesho (self ringing bell) to Ieyasu TOKUGAWA. The Tokugawa shogunate created clock engineers called "otokeishi," and the history of Japanese clocks had started since then.
Characteristically, general clocks use the teijiho (system of uniform length hours), a timetable which divides a day into 24 equal parts, as a leading rule.
In contrast, Japanese clocks are manufactured under the futeijiho (varying length system), which divides seasonally changing sun's celestial objects infestation into 6 equal parts.
Strictly speaking, in the Edo period, the length of day and night was not changed everyday, but changed every 15 days, so the clock device was set to it.
A clock runs at the constant speeds, so there were a method of replacing a clock face every 15 days (wari-koma dial) and a method of exchanging two kinds of tenpu (weights), one for day and the other for night (nicho-tenpu), automatically at the border between day and night (ake-mutsu [dawn], kure-mutsu [dusk]).
However, either method requires people to adjust time change every 15 days.
However, the perpetual clock shown in the image changes the position of the characters showing time on the clock face full-automatically.
This is an unprecedented revolutionary mechanism.
Since clocks were luxury goods and many of the holders were wealthy people at that time, many decorated clocks were also made. In addition, there were plentiful kinds of clocks, such as hanging clock, yagura-dokei (lantern clock), dai-dokei (clock with mounting), shaku-dokei (pillar clock with hour scale), makura-dokei (bedside clock), desk clock, keisan-dokei (paper weight clock), inro-dokei (medicine case clock), and pocket watch. Some clocks had alarms or karakuri (mechanism).
Shaku-dokei is a clock whose weight attached to the upper part of the reed-shaped box moves machines in the box, and whose clock hands attached to the weight show scale.
This is a unique Japanese clock technology.