  Starting from the experimental fact that a moving charge experiences the
Lorentz force and applying the fundamental principles of simplicity (first
order derivatives only) and linearity (superposition principle), we show that
the structure of the microscopic Maxwell equations for the electromagnetic
fields can be deduced heuristically by using the transformation properties of
the fields under space inversion and time reversal. Using the experimental
facts of charge conservation and that electromagnetic waves propagate with the
speed of light together with Galileo invariance of the Lorentz force allows us
to introduce arbitrary electrodynamic units naturally.
