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The Water Clock
The water clock offers another way of telling time. Can you tell what time it was when this picture was taken? (Hint: the blue globes on the left show the hours, the blue discs on the right, the minutes.)
How does the world’s largest children’s museum keep track of time? With the largest water clock in North America! Designed by French physicist and artist Bernard Gitton, the water clock was procured by the museum in 1989 with a contribution from Mr. and Mrs. Richard Wood. Since then, the clock has attracted crowds of visitors who marvel at its beauty and accuracy, and learn to tell time in a whole new way.
Gitton worked for almost five years to perfect the design of his first water clock. Thousands of mathematical calculations were made to determine the size of each minute disc and hour sphere and length of each pipe. However, designing the clock was not as difficult as constructing it to precise specifications. Gitton designed and supervised the creation of each hand-blown glass part, assembled the clock for testing and disassembled it for shipping to Indianapolis. Gitton and two assistants came here to assemble the clock and to train Mark Coovert in its care.
The clock, which is 26.5 feet tall, uses 70 gallons of a solution of water, methyl alcohol and food coloring. The alcohol prevents algae and fungus from growing inside the pipes while the food coloring allows visitors to see the clock’s function more clearly.
The water clock works on three basic principles of physics: energy cannot be destroyed only changed; gravity pulls objects down to the lowest possible level; and water seeks its own level.
Initially, an electric water pump beneath the floor moves the water to the top reservoir. From there it flows into a glass cupel (a shallow cup or scoop) attached to a green neon pendulum. As the cupel fills, the increasing weight causes its arm to dip (gravity) and empty the liquid.
The cupel then returns to an upright position, thus propelling the pendulum. This occurs every two seconds, keeping a steady stream of liquid flowing into the clock’s systems of curved pipes and siphons. Every hour, the minutes column empties, creating a vacuum that draws liquid into the hours column to fill one of the hour spheres.
Together the number of filled spheres lining the hours side of the clock and the number of filled discs on the minutes side tell visitors the time of day. Each disc represents two minutes.
There are only 29 of these minute discs, representing 58 minutes. The missing two minutes are accounted for in the time it takes for the pipes to drain. Just before one o’clock, the minutes and the hours sections are full. When they overflow they create a siphon that empties the entire clock and creates a dramatic event for visitors. Then the whole process begins again.
This picture was taken at 9:52 a.m.