Cesium Atomic Clocks
- Kinds of cesium clocks, with pictures, plus a description of their operation and the science behind them.
- http://tycho.usno.navy.mil/cesium.html

Smithsonian Institute - On Time
- History of the clock and how Americans have measured time and been affected by it.
- http://americanhistory.si.edu/ontime/

Doug's Atomic Clocks
- Details on Doug Hogarth's experiments with his atomic clock.
- http://www.niceties.com/atomic.html

How Stuff Works: Pendulum Clock
- Concise description using drawings and animation to show the operation of a pendulum clock.
- http://www.howstuffworks.com/clock.htm

How Stuff Works: Atomic Clock
- Concise history, background, definitions and operational information regarding atomic clocks.
- http://www.howstuffworks.com/atomic-clock.htm