Pellegrini and Swift have recently suggested that the use of special relativity in the calculation of the electric dipole moment of a moving magnetic dipole cannot be applied to the classic experiment of Wilson and Wilson, which used rotational motion. This paper contests that view. The disagreement arises in the choice of coordinates used to represent physical quantities measured in the rotating frame. The arguments of this paper are based on Einstein’s discussion of the validity of arbitrary coordinates and the difficulty in their interpretation. Because of the lack of synchronization of clocks, caution must be used in assigning values to physical quantities in the usual coordinates that describe a rotating frame. This paper gives the detailed transformations to an inertial rest frame, where the interpretation of measurements is assured. Other aspects of the rotating frame are also discussed.

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