The design of cables for high-frequency power transmission used in telecommunication, as well as for heating purposes, is based on the capacitance and thermal conductance of the conductor system employed. Capacitance and thermal conductance are equivalent problems of potential theory, and the author, after establishing the principle of equivalence, gives an account of the method of images for obtaining the potential on the surface of circular conductors. This method is first applied to a screened pair as used in high-frequency cables, and then generally to an even-numbered conductor system within a coaxial screen. General expressions for the potential functions are derived in the form of asymptotic expansions. A graph is given of the potential functions of the symmetrical and unsymmetrical systems of a screened pair, from which the capacitance, inductance and impedance can be found for a given design, and vice versa. Finally, the temperature rise of dielectrically-heated cables is treated, and it is shown that for this also the result can be expressed in terms of capacitances which may be obtained either from measurements or by computation.
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