The Conception of the Atomic Clock


    THE presidential address to the Section of Physics of the American Association for the Advancement of Science, which was delivered at Columbus on December 29 by Dr. Herbert E. Ives, is printed in Science(91, 79; 1940). The address is entitled “The Measurement of Velocity with Atomic Clocks”. Taking the variation of atomic clock rate as an experimental fact, established by the Doppler effect in hydrogen canal rays, and adopting also the Fitzgerald contraction of moving rods indicated by the Michelson-Morley experiment, Dr. Ives points out that it is possible to define Velocity’ in various ways, none of which has any a prioriclaim to be chosen as ‘correct’. The Restricted Theory of Relativity corresponds to the choice of one of them. “They are all deviations from the simple Newtonian concept of velocity”, says Dr. Ives, “which is in terms of rods and clocks which are unaffected by motion. I urge the merit of the Newtonian framework as the only unambiguous basis for the idea of velocity”. Dr. Ives does not consider that the ether has been “abolished” simply because it is possible to define velocity in a manner which makes it unnecessary to refer to that medium: he claims that the Sagnac experiment, in which beams of light moving in opposite directions round a rotating disk produce movable interference fringes, gives experimental evidence of the existence of the ether. His views, he says, “will be recognised as those of the earlier students of the subject—Fitzgerald, Larmor, Lorentz—but not of those who would shift the burden from variant measuring instruments to the nature of space and time”.

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    The Conception of the Atomic Clock. Nature 145, 417 (1940).

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