The Maxwell's electromagnetic equations are isomorphic to the motion
equation of a linear elastic continuum which is hard to compression
though liable to shear deformation. The Coulomb gauge expresses the
medium incompressibility. The magnetic vector potential corresponds
to the medium velocity. The pressure stands for the electrostatic
potential. The electric field is modeled by an external force whose
origin is beyond the elastic model. The electric charge corresponds
to a medium defect which produces the perturbation
δp ~ 1/r
of the pressure field. The defects interact with each other due to the
dilatation center in the core of the inclusion.