Appearance: Rectangular tall wooden case with going movement behind glazed top hood. Vertical dial markers.
Period: Early to late.
Escapement: Early single foliot, but generally later balance wheel.
Power Source: Lead weight, or suspended brass strike movement acting as weight.
Principles: These clocks were a unique Japanese invention which simply told time on a linear scale as the weight descended. Many versions exist of this type of clock, which were made throughout the Tokugawa period. The earlier ones first used the foliot, then the pendulum and finally the balance wheel. The principle is the same in all the various types of shaku-dokei.
Shaku is a Japanese unit of length, roughly a foot, and many of these pillar clocks are of this length, although by no means all. This type of clock probably developed from a lantern clock, a scale first being drawn on the pillar behind the clock. The next step was probably to have a back board for the hour marks with the exposed weight still falling in front and there are in fact clocks like this (there is an example in the Tokyo museum). It was a simple step from there to move the scale to the front, box the weight in and fit a marker to it. This marker can indicate either against linear movable chapters or against a graph type scale.
Most have noon in the middle of the scale, thus putting the time of wind at the convenient ‘commencement of dark’ position. Some start at the top at noon, usually a feature of later clocks. Initially the pillar clock was simple and less expensive to produce than a clock with a circular dial and movable chapters. Thus it was probably more popular and certainly many have survived.
There are several styles of dial plate:
A. Adjustable ‘temporal hour’ markers (plus half-hour markers on taller shaku-dokei) located in a groove running down a vertical dial plate and held in place with individual spring plates to rear. The aperture in the case is slightly wider on one side of the vertical dial plate to enable a pointer (hand) fixed to the going weight to point to the appropriate hour. Thus as the weight falls the ‘hour’ is indicated in succession. Temporal timekeeping is provided by appropriately adjusting the hour markers; normally every thirteen days.
B. Seven interchangeable double-sided dial plates replacing the single slotted dial plate above. Each dial plate provided differing temporal hour spacing for each 13 day period. (13 days x 14 options x 2 half years = 364 days). Typically the same dial plate could be used for mid-summer and mid-winter where the maximun variance for daylight or night was necessary. This solution of temporal timing eliminated the need for the difficult task of adjusting vertical hour markers. Few complete sets of these survive – usually the only one that was actually on the clock is left with it.
C. Single fixed wide dial plate with fourteen vertical divisions indicating temporal time for each of the 13 days of normal seasonal adjustments. Apertures on both sides of the dial plate enabled a cross bar to be fitted to either side of the going weight and to pass down the front of the dial plate. A sliding hand was fitted to this cross bar and was positioned to act as a time hand for the appropriate 13 day period. These dials are called ‘namagata’, or sea wave.
A development of the shaku-dokei was to incorporate a striking train by making it the weight for the going train. Striking was generally restricted to the movable temporal hour dials (A – above), however, there exists rare examples of namagata dials with strike. The release for the strike was activated by pins protruding from the vertical ‘hour’ markers.
Shaku-dokei were normally hang on the toko-bashira (square post) next to the tokonoma (alcove) of a Japanese room. Mounted on this structural pillar they took up little space. The smaller versions were very often mounted in small alcoves or even in tansu chests.
With the introduction of European time, it occurred to the Japanese clockmaker that these clocks might be adapted to the new system, and accordingly we find some specimens in which, instead of the Japanese set of scales, a single scale has been substituted, side by side with the old “hour” plates, which shows the time in equal hours commencing with twelve noon, and graduated in divisions of one-fifth through all the twice-twelve hours of our clocks.
Examples: Shaku-dokei in author’s collection.