Clocks, Atomic Caesium atomic clock, 1955

Clocks, Atomic Caesium atomic clock, 1955. This was the first atomic clock and, when developed in 1955,Ê the most accurate timekeeper in the world. The timekeeping depends on the vibration of caesium stones - a natural phenomenon. It consists of an airless tube, which allows caesium atoms to pass along it while simultaneously exposing them to very high frequency radio waves. Isidor Rabi was the first to suggest using the stable vibration of caesium as a time, or frequency, standard in his Richtmeyer Lecture to the American Physical Society in 1945. In 1953, Louis Essen and Jack Parry developed the idea at the National Physical Laboratory in the UK, and their work yielded this clock, which is accurate to one second in 300 years. Now international time is defined by atomic, not solar, seconds. ©SSPL/Science Museum