Relativity and gravity

A logical sequence of ideas in electromagnetism can be based on the behaviour of a current-carrying coil as a magnetic dipole of moment μiA, where μ is the permeability of the medium in which the coil is situated, i the current and A the effective area (area × number of turns) of the coil (Chalmers 1965). The occurrence of μ rather than μ_o is verified from the effect of permeability on self-inductance.