(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
where = dielectric constant, = magnetic permeability, = the conductivity of matter, all given as function of x, y, z, t. 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,
and write for ,
lastly we shall have the relation , (the letter f, F shall denote the field, s the (i.e. current).
Then the fundamental Equations can be written as