摘要
The set of equations governing a system consisting of an electromagnetic field plus charges in it is obtainedby varying the appropriate action. It is not assumed that the currents are given, which in fact leads to the Maxwellequations governing the fields. Nor is it assumed that the fields are given, which in fact would lead to the determinationof the motions of the charges (the currents) through the Lorentz force. On the contrary, currents and fields are left freeto interplay, and they can be found simultaneously from the equations obtained.
