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The King James clock was known as the Eltham Perpetuum, and was famous throughout Europe. It is mentioned in two works of Ben Jonson. Clocks powered by atmospheric pressure and temperature changes were subsequently developed by Pierre de Rivaz in 1740, [3] and by James Cox and John Joseph Merlin (Cox's timepiece) in the 1760s.
In August 2004, NIST scientists demonstrated a chip-scale atomic clock that was 100 times smaller than an ordinary atomic clock and had a much smaller power consumption of 125 mW. [ 33 ] [ 34 ] The atomic clock was about the size of a grain of rice with a frequency of about 9 GHz.
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The caesium atomic clock maintained by NIST is accurate to 30 billionths of a second per year. [206] Atomic clocks have employed other elements, such as hydrogen and rubidium vapor, offering greater stability (in the case of hydrogen clocks) and smaller size, lower power consumption, and thus lower cost (in the case of rubidium clocks). [206]
Commercial rubidium clocks are less accurate than caesium atomic clocks, which serve as primary frequency standards, so a rubidium clock is usually used as a secondary frequency standard. Commercial rubidium frequency standards operate by disciplining a crystal oscillator to the rubidium hyperfine transition of 6.8 GHz (6 834 682 610.904 Hz).
Telechron electric alarm clock. Telechron alarm clocks are particularly popular with collectors. Until about 1940, the overwhelming majority of Telechron alarm clocks had bell alarms. The entire mechanism was enclosed in a bell housing of steel. Atop the clock's coil was a metal strip that vibrated at 60 cycles per second when the alarm was ...