 For example, with this model transmission lines and power grids were developed and radio frequency communication explored.An effort to mount a full-fledged electromechanics on a relativistic basis is seen in the work of Leigh Page, from the project outline in 1912 to his textbook "Electrodynamics" (1940) The interplay (according to the differential equations) of electric and magnetic field as viewed over moving observers is examined.What is charge density in electrostatics becomes proper charge density and generates a magnetic field for a moving observer.