By means of the generalized, Galilei covariant Maxwell equations for inertial frames S(r,t,w) with substratum velocity w, Fitzgerald contraction = o 1- - co 2 2 1 2 bv wg of rods, Larmor dilation t = t o 1- - co 2 2 1 2 bv wg of clock periods, and velocity dependence of particle mass m = mo 1- - co 2 2 1 2 bv wg are shown to be Galilei-invariant vacuum substratum effects, where v - w = v?= inv is the respective object velocity relative to the substratum frame S (r?,t?,0). The Lorentz force transferred through the substratum is Galilei-invariant, F = e[E?+ w ? B + (v ? w) ? B ] = e(E? + v? ? B?) = inv. The kinetic energy K(v?) of high-velocity particles is given by the Galilei-invariant mass-energy relation K(v?) + Eo = mo(v?) co 2 , where Eo = mo co 2 (mass-energy equivalence). The Galilean measurement process in inertial frames S(r,t,w) is explained considering physical length contraction of measuring rods and rate retardation of measuring clocks, as well as synchronization of clocks in absolute time. Crucial experiments underlying Galilean electrodynamics are discussed briefly.
