  An approach to the teaching of electromagnetism to senior undergraduate
students, designed for overcoming the fragmentation of the theory is described.
As usual it starts from the static case, but it is strictly based on Helmholtz
theorem of uniqueness of vector fields, on primary experimental observations
upon the sources of electric and magnetic fields, on Lenz's law and on
principles of superposition and reciprocity of interactions. Thereafter,
without further postulation, all laws and rules arise in a procedure where
electricity and magnetism parallel one another. Maxwell's equations are built
up on a step-by-step basis, showing that electromagnetic field can be
considered but a twofold linear vector field obeying the simplest principles of
physical theories. It is shown that every system of units fits this formalism,
provided suitable values are assigned to some constants arising therein from
superposition principle.
