A re-examination of physics from Maxwell to Einstein leads to a new unified theory of electricity, magnetism, inertia and gravity in which gravitational potential slow clocks, and motion at near light speeds produces real causal effects of increases in mass and slowing of clocks. The magnetic field is seen as a real entity having energy density, directional properties, position, and motion. Light ... [Show full abstract] travels at a constant speed relative to a local background created by the presence of the electric fields of all charged particles and is a weighted average of their velocities. Space and time are regarded as Newtonian; time dependent processes slow and photons are acted upon by gravity curving their path. Magnetic fields draw their energy from work done altering the motion of charges involved in their generation and magnetic forces result from the exchange of energy. Inertia is thus explained as an electromagnetic phenomenon. Electric fields are 4 dimensional with potential as the fourth dimension and gravity is a by-product of the distortion of space by their combined internal stress.