Polarization fluctuations in regions bounded by equi-potentials

It is shown that the integral of <{P(rτ), P(r')}>· n̂ as a function of r over a volume Ve bounded by an equi-potential is independent of r' and of Ve and is determined solely by [ϵ(ω)−1] · n̂ provided the dielectric constant is local and that Ve is of macroscopic dimensions.