1.The double electrical layer is a consequence of two factors: charge transfer through the surface and dipole surface polarization. If the dipole moment exceeds 0.7 0.8 D, the latter becomes decisive, and the former may be neglected; the converse is true for nonpolar materials. 2. Gezekhus's and Coehn's rules apply only to insulators for which dipole polarization is absent or negligible (dipole moments less than 0.2 0.4 D). 3. Only the dipole moment governs the mechanical strength, dielectric constant, and electrification if the dipole moment is over 0.8 D, so the result is the reverse of that predicted by Gezekhus's and Coehn's rules if the dipole moment is negative, namely the negative member of the pair is the one of higher strength or higher dielectric constant.