Environmental Engineering Reference
In-Depth Information
u
Telling Time
with Water
One early use of water power was to tell time. The
ancient Greeks called a water clock a clepsydra, which
means “water thief.” The earliest clepsydras had water
that fl owed out of a hole in the bottom of a container.
The sinking level of the water in the container marked
the passing of time. A little more than 2,000 years ago,
a Greek inventor created a mechanical water clock.
In this clepsydra, water fl owed from one container to
another. The rising level of water in the second container
pushed up a small disk that fl oated on the surface. The
disk was connected to a rod that marked the passing
of hours as it moved upward. Some water clocks also
powered gears. As the gears turned, they moved small
models of humans or dropped stones onto a gong.
In 1086, a Chinese inventor named Su Sung built a
water clock that was about 40 feet (12 meters) tall. In
the clock, 36 buckets were attached to a water wheel.
When one bucket fi lled with water, its weight made the
wheel turn, bringing up the next bucket. The movement
of the buckets marked time.
Across the world, about the same percentage of energy comes
from hydroelectricity. China is the world's leading producer
of hydroelectricity. In 2006, its dams generated 431 billion
kilowatt-hours of electricity. Norway gets more of its electricity
