The constitutive relations between the D and F tensors, proposed by Minkowski for a linear materials (that is, E is proportional to D and B proportional to H), are: D μ μ ν ν u ν ν = c 2 ε ε F μ μ ν ν u ν ν ⋆ ⋆ D μ μ ν ν u ν ν = 1 μ μ ⋆ ⋆ F μ μ ν ν u ν ν where u is the four-velocity of material, ε and μ are respectively the proper permittivity and permeability of the material (i.e. in rest frame of material), ⋆ ⋆ and denotes the Hodge star operator.