In the traditional sense of the term, a clock is a mechanical device made up of an oscillator whose movement is maintained by the regular distribution of a driving force. This force can originate from either a weight or a spring. The energy is distributed to the oscillator by means of a gear train and an escapement system that allow the even transmission of small amounts of force. (See Figure 1.) The gear train then moves the clock’s hands, which rotate in a clockwise direction on a face divided into 12 hours. The entire mechanical system is encased in a cabinet or other type of housing.
Among the many types of clocks that have been created throughout history, there are some that stand out by their truly unusual and original nature. They are constructed in such a manner that the viewer is surprised or amused by their appearance or the manner in which they function. The Watch Museum at La Chaux-de-Fonds, Switzerland has many unusual clocks in its collection and presented a very special exhibition of these uncommon timekeepers during the summer of 2001. A small sampling of some of the more ‘common’ uncommon clocks is presented here for your enjoyment.

Unconventional energy sources
In most clocks, the movement is generally powered by a descending weight, by the unwinding of a spring or by an electric battery. The following three clocks are examples of mechanisms that do not have any of these. Their rather unconventional energy sources are both surprising and amusing.

Clepsydra or water clock
Before the invention of mechanical clocks, the Egyptians and the Greeks used the sundial and the clepsydra or water clock to tell the time. (See Figure 2.) In its basic form, water drips from one vessel into another that is graduated to indicate specific intervals of time.
Around 1980, an ingenious individual came up with the idea of combining water, as a driving force, with a mechanical movement regulated by a pendulum. Made of Plexiglas and measuring about one metre in height, this clock features a jet of coloured water as its energy source. A pump is hidden under the lower reservoir and circulates the water in the closed system. In reality, it is the electric pump that is the true source of energy since it moves the water.
The pendulum is the regulating organ of this system, which is made up of two vessels on the upper part of the apparatus that alternately fill up or empty depending on the position of the pendulum. The movement is thus energized and moves the second wheel as the pawl (or click lever) acts on the pins. As the upper vessels empty, they alternately fill up two other small basins located below them. The two lower basins are mounted on a lever. Since it is inclined either to one side or another, only the higher reservoir can fill up, which then tends to tip the lever in the other direction. It can do this only every 30 seconds since it has a retaining arm that hits up against a half-moon mounted on the second wheel. As this arm moves from left to right, it advances the minute by turning the minute wheel and its hand as the pawl or click lever acts on one of the 60 pins .
The hour hand is connected to the minute hand by a coaxial disk. It is also equipped with 60 pins, each of which moves only every 12 minutes since 5 of the 60 pins of the minute wheel are located closer to the axis, allowing the click lever to act against a pin of the hour wheel. This therefore gives 5 jumps per hour and one revolution in 12 hours. It is clear that the operation of this clock is completely different to a classic clock.

The Atmos clock
In 1928, the engineer J.-L. Reuter realized the first clock that ‘lives on the air of time’. Produced by Jaeger-LeCoultre in the town of Le Sentier in Switzerland, the Atmos enjoyed an immediate success, and still does to this day. Its energy source comes from the variations in temperature of the ambient air. These variations then affect the gas contained in a metallic casing that is expandable like an accordion. This casing is housed in a solid compartment and is compressed by a strong spring. The fluctuations in temperature cause the pressure of the gas to vary in such a manner that the box’s cover moves in one direction or another depending on whether the exterior temperature rises or falls.
The movement of the cover acts on a second spring whose coils are either loose or compressed. When it relaxes, it pulls on a small chain that is connected directly to the arbor of the barrel that in turn winds the spring motor of the clock. The coiled spring is slightly weaker than the mainspring so that it cannot be overwound. In this way, there is no risk of applying too much force and breaking the mechanism. Winding occurs only as needed.
The regulating organ of the Atmos is a torsion pendulum, made up of a fine wire holding a heavy weight. It moves very slowly and makes one oscillation per minute, which consumes very little energy. The Atmos can function for more than one year by drawing on the reserve contained in its mainspring. Since it winds itself drawing on the small temperature variations, it can theoretically continue to operate indefinitely without manual winding. As an example, (no advertising intended), my own Atmos has been operating perfectly for the last 20 years. Of course, it is necessary to have it serviced from time to time, or to even change the motor since it might lose some of its gas over the years. The success of this clock lies in the extraordinary energy economy of this unique system.

The potato clock
This is a rather odd name for a clock, yet it is an accurate description of its appearance (see Figure 4). It is actually a small quartz clock that is equipped with a liquid crystal display but that, very uncommonly, uses potatoes as its energy source. In actuality, it works using electricity as any other quartz clock but since it uses so little energy, the battery has been replaced by two potatoes! Two pairs of copper-zinc electrodes are inserted in each potato, offering a rather novel example of the Volta battery. It works as long as the potatoes remain moist. When they dry out, they can be replaced by another pair, as one would replace a spent battery. The potatoes have the advantage of not polluting the environment and can even be eaten!

Evaluation of the energy consumed
It is an interesting exercise to compare the energy consumed by these three unconventional clocks. My calculations are based on estimations but they are accurate to an order of magnitude.
As for the clepsydra or water clock, assuming that the pump raises one cubic centimetre of water to a height of one metre in one second, the power dissipated is:
P = mgh/t = (0.001)(10)(1)/1 = 0.01 watt
The energy thus consumed in one day is equal to (0.01)(86400) = 864 Joules. This is enormous for a clock!
In the case of the Atmos clock, the calculation shows that the energy consumed is about 0.050 Joules per day, which is about 17,500 times less energy than the water clock.
Concerning the potato clock, the energy consumption is approximately the same as a digital watch, or about 0.175 Joules per day. This means that it uses about 5,000 times less energy than the water clock and 3.5 times more energy than the Atmos.
It can be stated that, in general, the energy use of a regular clock, whether a small table model or a large tower clock, lies somewhere between the limits of the Atmos and the water clock. R Unusual escapements
The clocks discussed below are unusual in that they utilise a very different type of escapement mechanism than ‘normal’ timekeepers.

Mystery clock
The example shown in Figure 5 was created by A.-R. Guilmet in Paris around 1870. The black marble base contains the movement and the bronze figure holds the oscillating pendulum. The mystery resides in the way that the pendulum is connected to the clock’s movement. The statue rests on a mobile platform that is activated by a modified classic escapement. The displacement of the platform and the statue is imperceptible but is enough to maintain the oscillations of the pendulum, which then operates the escapement.

The Audacious clock
The name of this clock derives from its design, which is totally different than ‘normal’ classic timekeepers (see Figure 6). It was created for a competition by students attending a course on clock restoration under the supervision of Jean-Michel Piguet. The general conception was based on a prototype that I had made some time earlier. The elaboration of the Audacious clock also included the participation of students at the Art School in La Chaux-de-Fonds for the overall aesthetic design.
The display of the time is obtained by rotating spiral-shaped cams behind a plate graduated to indicate the hours and minutes. The seconds are estimated based on the position of the cam, but without any graduations.
The idea was to have only one gear, with the barrel connected to the pinion of the minute wheel. The gear ratio is 1:12, which means that the barrel makes one revolution in 12 hours. It drives the cams by friction. A gilded cam indicates the daytime hours and a dark blue cam indicates the night hours. In the same manner, the minute wheel carries two cams indicating the minutes.
The clock in the figure reads 12:47 in the afternoon. The gilded hour cam touches the 12:30 and the minute cam is at the 17, giving 12:47 in the daytime. It would be easy to replace this unusual display by a more classic display. However, even though the clock would be a little simpler to read, it would certainly lose its originality.
Another particularity of this clock is its unusual escapement (Figure 7). The very heavy pendulum marks the half-second and moves the second wheel by means of the click lever once per second. Each minute, the second wheel frees the minute wheel by moving the retaining lever. This restores to the pendulum the energy lost during the past minute. Because of its construction, this escapement loses 119 vibrations since it gives only one impulse for every 120 vibrations.

Day and night displays
Before the invention of luminescent material and electrical lighting, it was difficult to know the time at night. Clocks equipped with chimes used in clock towers and even smaller clocks that decorated fireplace mantles and furniture in homes became popular. They often had repeater mechanisms, which allowed the chime to be repeated by pulling on a cord. Another method of telling the time during the night was to use a special lamp placed behind the display of rather primitive clocks. They provided, however, only an approximate reading of the hour.

Night clocks
Figure 8 shows a Swiss night clock that was made during the middle of the 18th Century. The mechanical movement turns the face that has been marked with 12 Roman numerals and that carries a marker indicating the hour on the inner fixed face. In the daytime, the movable face shows the time on the fixed face. At night, the hours of the movable face move to the cut-out on the face and a light shines through, indicating the time. In this way, depending on the light source, whether sunlight or lamplight, a different method of displaying the time is used.
Another example of a night clock is shown in Figure 9. Made by Pierret et Cie in 1868, this unique clock features an opaline glass globe lighted from the inside. It is divided into 12 hour indications along its circumference and makes a complete revolution in 12 hours. The time is indicated by a marker fixed on the base of the globe. This unusual and decorative clock can also serve as a lamp.
To be continued in the next issue…