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It is well known that the dielectric constant of a dielectric which is perfect, homogeneous and isotropic obeys the Clausius-Mossotti law* 1•2•3:in which e is the dielectric constant, M the molecular weight, d the density.The constant has the dimensions of a volume and is called the molecular polarization. It is defined by the relation in which N is Avogadro's number and a is the molecular polarizability.The Clausius-Mossotti law can also be written as follows: in which n is the number of molecules per unit volume.When the Clausius-Mossotti law is written as above, the use of the Gauss C. G. S. system of units (dielectric constant and magnetic permeability of vacuum both equal to unity), or of the electrostatic C. G. S. system of units (dielectric constant of vacuum and velocity of light both equal to unity) is required. The law cannot be used as such in the electromagnetic system of units (magnetic permeability of vacuum and velocity of light both equal to unity) or the practical system of units (unit of length = 199 cm., unit of mass = io-u gm., unit of time = 1 second, magnetic permeability of vacuum and velocity of light both equal to unity). In these two systems of units the numerical value of the dielectric constant of vacuum is 1 /goo.The purpose of this note is to give the Clausius-Mossotti law a form independent of the system of units and to derive it in a general way applicable to all dielectrics which are perfect, homogeneous and isotropic, including those which are permanently polarized. The derivations of the Clausius-Mossotti law usually given in text-books implicitly suppose that the Gauss C. G. S. or the electrostatic C. G. S. system of units are used and fortuitously give the correct result for permanently polarized dielectrics.

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Some aspects of the mode of formation of anodic oxidation films in the potential region below oxygen evolution were examined for a number of metals under as nearly constant experimental conditions as possible. The metals selected were Al, Ti, Hf, V, Nb, Ta, and Cr. Results for Zr were reported in earlier publications. Electrolytic parameters and formation fields were evaluated from the unitary formation rates. Local currents were estimated using the method described previously.