Essen and Parry: a caesium atomic frequency and time standard

What changed

Reported a caesium resonator apparatus operated as an atomic standard of frequency and time interval at the National Physical Laboratory.

Scientific scope

The record is the exact 1955 Nature paper and apparatus. Earlier molecular-beam resonance work, later astronomical calibration, the 1967 SI-second definition and later caesium fountain clocks remain separate.

Evidence

The linked sources identify this contribution and its scope. WRS has not independently reconstructed the scientific claims. The record is the exact 1955 Nature paper and apparatus. Earlier molecular-beam resonance work, later astronomical calibration, the 1967 SI-second definition and later caesium fountain clocks remain separate.

Contributors

• L. Essen · SCIENCE: Named source author of the scoped work; individual effort shares are not measured.
• J. V. L. Parry · SCIENCE: Named source author of the scoped work; individual effort shares are not measured.

• Essen and Parry, An Atomic Standard of Frequency and Time Interval
• NPL account of the 1955 caesium atomic clock

Provisional WRS assessment, edition 2026-10-16.1. Independent expert calibration is pending. This grade does not certify correctness or assign ownership.

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