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The design of vacuum-tube oscillators for induction heating involves many factors not usually encountered in radio practice. The choice of the circuit to be used, the tank current, operating frequency, and the physical construction are dependent upon a knowledge of the theoretical and practical requirements of induction heating, and an understanding of the operating conditions to be met in the average factory. It is concluded that either the Colpitts or the coupled-grid circuit meets the requirements, and an operating frequency in the neighborhood of 500 kilocycles, with a tank current of from 100 to 300 amperes is desirable. In this paper, the induction-heating theory necessary to substantiate the above conclusions together with a brief discussion of the other factors involved is presented.