Abstract
THE most accurate timekeepers of to - day are divided into two classes, depending on whether the restoring force of the oscillator is gravity, as in pendulum clocks, or elasticity, as in quartz crystal oscillators. In a monograph by A. L. Loomis and W. A. Marrison on precision clocks, published in the Transactions of the American Institute of Electrical Engineers, an account is given of the performance of a set of 100,000-cycle quartz oscillators built by the Bell Telephone Laboratories for use as a primary frequency standard. The frequency of quartz oscillators is practically independent of the amplitude. They are not affected by gravity or magnetic fields and can be easily shielded from electrostatic fields. They are practically unaffected by heavy traffic in neighbouring roads or by the vibrations near earthquake zones. A crystal clock standard is more costly than a pendulum clock of the highest precision, but it can be used for many purposes. For example, an absolute comparison of crystal clocks can be made with an error of less than one hundred-thousandth part of a second, and can be maintained continuously. For short time comparisons an inaccuracy not greater than 1 in 1010 has been obtained. The high accuracy of comparison is due chiefly to the fact that the number of vibrations is 200,000 times greater than with a '‘seconds pendulum. A comparison made of the data obtained by observing the difference in the rates of a crystal clock and three pendulum clocks revealed for the first time a lunar day variation. This is due to the fact that the crystal does not respond to variations in the gravitational effect of the moon, while the pendulum does. The difference in the rates of the clock and the crystal timekeeper thus contains a term depending on the period of the lunar day.
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Modern Developments in Precision Clocks. Nature 130, 124 (1932). https://doi.org/10.1038/130124b0
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DOI: https://doi.org/10.1038/130124b0