When electric charges are at rest, or, what
amounts to the same thing, they are involved in a common motion of uniform
translation, formulas (13) and (20) reduce to
This is Coulomb’s law. It is clear, moreover, that
the quantities of electricity are measured in electrostatic units in our theory
as in that of Lorentz.
With Lorentz, we consider ponderable dielectrics
as formed of positive and negative electric atoms, the total charge of each
element of volume being nil. These atoms are subjected to elastic forces,which
tend to bring them back to their position of equilibrium when they have been isolated
from exterior forces. The polarization of dielectrics and its effects are thus
explained in the same manner in both theories and will give cause to the same
relations.