We show that no charges exist inside the conductors and . With (8) and (28) we obtain from (26) and (27) for the electric field

We denote the coefficient of on the r.h.s. by . Taking the divergence and neglecting a spatial variation of this coefficient and of the derivative , which may result from the temperature variation, we obtain, using the Maxwell equation

the following equation for the charge density :

stands for the Laplacian. Under stationary conditions as assumed the heat conduction equation

where denotes the specific heat per volume, leads to

which reduces eqn. (33) to the homogeneous differential equation

where

is a screening length of atomic dimension. Inside a conductor the solution of eqn. (36) decays to zero exponentially within a distance from the surface given by . (We note the following analogy: In the London theory of supraconductivity an equation of the same form as eqn. (36) describes the expulsion of the magnetic field from the interior of a superconductor (Meissner-Ochsenfeld effect) [3].) On a macroscopic scale, therefore, the condition of charge neutrality

holds. The charges generating the thermoelectric potential must be located exclusively at surfaces and interfaces!