Maxwell's Equations, the Relativity Principle and the Objectivity of Measurement
The interpretation of the velocity parameter in Maxwell's equations and the Lorentz Force law is examined. It is shown that the predicted trajectories of electrons in an electromagnetic field depend on the state of motion of the observer. This ambiguity can be removed by assuming that the origin of the field is the unique reference system for determining the electron velocity in these equations. The same convention is recommended for the definition of the momentum of particles in general. Accordingly, it is assumed that observers will only disagree on the results of measurements because they employ different systems of physical units in their respective rest frames. This situation needs to be recognized in applying Galileo's Relativity Principle (RP), particularly with respect to the transformation properties of physical laws in different rest frames.