Formal expressions are derived for the space currents and electrode currents produced by a sinusoidal potential difference of angular frequency ω applied between a pair of electrodes at a distance d apart and immersed in a gas discharge. It is shown that the ionized gas behaves like an isotropic medium of dielectric constant {1 - 4πne²/mω²} and zero conductivity only in the limiting case of βidentical withν/ωd<<1 where ν is the r.m.s. velocity of the free electrons in the gas. The variation of the equivalent dielectric constant and conductivity of the gas with β are sketched. Extensions of Green's reciprocation theorem and of a theorem on induced currents given by W. Shockley are derived in the appendix.