Physicist James Clerk Maxwell was perhaps the first to recognize that atoms could be used to keep time. The circuits were accurate enough to measure and record variations in the Earth’s rotation, but they were still limited in performance and sensitive to environmental changes. It kept time according to the mechanical resonance of vibrating crystals of piezoelectric material-which created electrical signals with a precise frequency. In the 1920s the quartz crystal oscillator circuit was invented. A BRIEF HISTORY OF TIMEKEEPINGįor thousands of years the reference for timekeeping was the Earth’s rotation rate-which was limited in accuracy. Administered by the IEEE History Center and supported by donors, the milestone program recognizes outstanding technical developments around the world. This month the atomic clock received an IEEE Milestone. The clock kept time by tracking the microwave signals that electrons in atoms emit when they change energy levels. The clock helped redefine the duration of a single second, and its groundbreaking accuracy contributed to technologies we rely on today, including cellphones and GPS receivers.īuilding on the accomplishments of previous researchers, Harold Lyons and his colleagues at the U.S. National Bureau of Standards (now the National Institute of Standards and Technology), in Washington, D.C., began working in 1947 on developing an atomic clock and demonstrated it to the public two years later. THE INSTITUTEThe invention of the atomic clock fundamentally altered the way that time is measured and kept.
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