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Escapement (Public Radio Commentary)

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(For radio stations: Bill's public radio work can be licensed via PRX).

This past Sunday we performed the ritual of setting our clocks back for daylight savings time. In doing so we paid homage to the most world-changing invention of the western world: A small device called an escapement - the device that gave the clock its tick-tock sound.

You see, all mechanical clocks are driven by a weight, like a pendulum, or a tightly wound spring. The escapement restrains the motion of that weight or the unraveling of the spring, making them move precisely and evenly. The escapement made time portable, divorcing it from the natural cycles of the Earth. In fact, the first clock makers found that moving away from telling time using nature was the key to inventing the escapement.

They modeled their first clocks on nature. The sun marked the time by moving slowly through the sky. So, early time keepers built sundials to chart the sun's progress minute-by-minute. Sundials, though, didn't work at night, and couldn't be easily moved.

The next model for time measurement was the flow of a river. The Chinese built elaborate clocks where water flowed from one vessel to another. By watching the level rise the Chinese measured the passage of time. Although an elegant way to measure time, the water limited the clock to warm climates - and still it wasn't portable.

Although ingenious, these solutions to measure time erred in emphasizing a continuous movement or flow to mark the time. The essential insight that allowed time to go portable, to be completely independent of nature and its elements, was not a smooth continuous motion, but regular, precise pulses.

In the 13th century some anonymous genius figured out how to turn the continuous unwinding of a spring into regulated bursts that moved the hands of a clock. The heart of a clock is a toothed gear, which is spun by a spring. Unimpeded, the spring would naturally turn the wheel faster and faster until the spring completely unwound. To prevent this, a small lever called the escapement, rests on the notched gear, alternately letting the gear move, then restraining it. Think of it as a seesaw sitting on the gear: It rocks one way letting the wheel move forward, but then totters down on the other side stopping the movement, repeating this until the clock winds down. This, of course, makes the clock go tick-tock.

The endless series of uniform motions from that escapement let us capture time, causing an explosion in time keeping and a revolution in our way of life: By the 18th century the Western world was producing 400,000 mechanical clocks a year. These clocks allowed our lives to have shape and form independent of the sun and the moon and the movement of the planets, thus revolutionizing our lives. As one historian has said, "The clock, not the steam engine, is the key machine of the modern industrial age."

Copyright 2004 William S. Hammack Enterprises