PROTOTYPE OF THE 'CLOCK OF THE LONG NOW'

This prototype, designed by Danny Hillis, was built by the Long Now Foundation to explore the mechanism for a clock intended to keep time for 10,000 years. The final version of the clock would be an enormously enlarged version of the clock shown here - a vast mechanism of architectural scale, big enough for visitors to walk through.

To reduce wear, the clock uses a torsional pendulum which rotates slowly and the clock ticks only once every 30 seconds. It is driven by falling weights which are rewound regularly. The full-size example would be powered by the energy from the footfalls of visitors or by changes in temperature. Any drift in the clock's rate will be corrected by a mechanism sensing the sun passing overhead at noon.

The stack of disks in the lower part of the clock is a train of adding wheels - a binary mechanical computer that counts the hours, the calendar and solar years, the centuries, and the phases of the moon and the zodiac. This also drives the display on the face of the clock which shows the changing pattern of the night sky continuously throughout the life of the clock. Each hour, the clock performs a visible calculation to update the dial display.