Introduction. The concept of heat flow under a thermal driving force or temperature difference with the applied analogy to the flow of electric charge under an e.m.f. has given rise to the well-known concept of thermal resistance, which has been made the basis of a model method of studying heat-flow problems by the construction of equivalent, electrical circuits. Proposed by Langmuir, Adams and Meikle1 this method has been developed by Beukin2 and by Paschkis3, to deal with transients as well as steady-state heat flow. Since, as these authors claim, oscillatory phenomena are not observed in heat-flow problems the thermal circuits are non-inductive and may be represented by electrical models consisting of resistances and capacities.