I have revised the general theory of physical quantities and I have de
monstrated that the system of primary quantities of electrodynamics is
as unique as the system of the general laws of physics. I have identi
fied three principles of electrodynamics with which help I have genera
lized the laws on the assumption of mobile conductors. I have demonstr
ated that Maxwell's and Lorentz's postulates are theorems of electrody
namics.