The oldest type of clock is a sundial clock, also called a sun clock. They were first used around 3,500 B.C. Sundials use the sun to tell the time. The shadow
of the sun points to a number on a circular disk that shows you the time.
Around 1400 B.C. water clocks were invented in Egypt. A water clock was made of two containers of water, one higher than the other. Water
traveled from the higher container to the lower container through a tube. The containers had marks and the water level told the time.
Before pendulum clocks were invented, Peter Henlein
of Germany invented a spring-powered clock around 1510. It was not very
precise. The first clock with a minute hand was invented by Jost Burgi
in 1577. It also had problems. The first practical clock was driven by a
pendulum. It was developed by Christian Huygens around 1656. By 1600,
the pendulum clock also had a minute hand.
Quartz is a type of crystal that looks like glass.
When you apply voltage, or electricity, and pressure, the quartz crystal
vibrates or oscillates at a very constant frequency or rate. The
vibration moves the clock's hands very precisely. Quartz crystal clocks
were invented in 1920.
The most accurate clocks today are atomic
clocks. They receive a radio signal once a day from the Atomic clock in
Colorado,which resets them. They automatically correct for daylight
savings time and are gauranteed to be accurate to wihin one second a day.
