Mushi-haguruma (Bug-shaped Gear System)

The Edo era Japan used a temporal hour system which fixed time by means of the dawn and the dusk.

ikkoku is a length of time which divides each daytime and nighttime period by six and was used as a unit until the early Meiji period.
The Length of ikkoku is about two hours; however, it differs day to night and also changes with the seasons.
In old Japanese-style clocks, the length of ikkoku was adjusted by hand twenty-four times a year, at the start of each of the twenty-four seasons in the lunisolar calendar.
Man-nen Dokei, however, didn't need to be manually adjusted because the clock automatically changed.
A key part of this function is the Mushi-haguruma (the Bug-shaped gear system).
The length of 1 daytime koku is longer moving toward the summer solstice, and shorter moving toward the winter solstice.
That means the Man-nen Dokei needed a device which reversed the movement of the machine at each solstice.
The mushi-haguruma accomplished this.
Please push the "Bug-shaped gear working model" button in the exhibit hall and you can see how it works.