(i) Curl m - δe/δt = C,
(ii) div e = lρ.
(iii) Curl E + δM/δt = 0,
(iv) Div M = 0.
(2) Further relations, which characterise the influence of existing matter for the most important case to which we limit ourselves i.e. for isotopic bodies;—they are comprised in the equations
(V) e = ε E, M = μm, C = σE.
where ε = dielectric constant, μ = magnetic permeability, σ = the conductivity of matter, all given as function of x, y, z, t; s is here the conduction current.
By employing a modified form of writing, I shall now cause a latent symmetry in these equations to appear. I put, as in the previous work,
x₁ = x, x₂ = y, x₃ = z, x₄ = it,
and write s₁, s₂, s₃, s₄ for Cx, Cy, Cz (√-1)ρ.