Travelling-field theory of induction-type instruments and motors

For many years, controversy has raged about the best method of analysing the behaviour of induction-type instruments. On the one hand, the idea of a travelling field, appropriate to the induction motor, has been advanced for these instruments without much conviction. On the other hand, the technique of superimposing forces of interaction between one component of the magnetic field and the induced current of the other has been shown to offer a reasonable explanation. In view of the development of this type of instrument for radio measurements, consideration has been given in this paper to the basic conception of absorbing the momentum of a travelling field as a means of producing a mechanical force proportional to the power dissipated, and also to the application of this idea in examining the operation of induction-type instruments and motors. A simple theory which appears to be satisfactory over a wide range of frequencies emerges from this approach.