(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) | , |

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 ,

further

for ,

and

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

(A) |