The equivalence principle and the correct form of writing Maxwell's equations

It is well known that the speed cu = 1/√ 0μ0 is obtained in the process of defining SI units via action-at-a-distance forces, like the force between two static charges and the force between two long and parallel currents. The speed cu is then physically different from the observed speed of propagation c associated with electromagnetic waves in vacuum. However, repeated experiments have led to the numerical equality cu = c, which we have called the c equivalence principle. In this paper we point out that ∇× E = −[1/( 0μ0c)]∂B/∂t is the correct form of writing Faraday’s law when the c equivalence principle is not assumed. We also discuss the covariant form of Maxwell’s equations without assuming the c equivalence principle.