The chief aim of the vibration engineer is to prevent the occurrence of structural failure due to excessive vibration. A secondary aim of only slightly less importance is to ensure comfort for personnel by the elimination of physiologically unpleasant vibrations; this consideration is a vital factor in the effective design of operational aircraft. The technique of vibration research is largely a matter of detecting and avoiding resonant conditions, and any method of predicting natural frequencies by calculation is welcome if only because it offers the possibility of reducing the practical testing programme.

It has long been realised that there is a precise analogy between the properties of vibrating mechanical systems and those of alternating current electric circuits. It was from this analogy that the concept of “ mechanical impedance ” (more appropriately termed “ dynamic stiffness ”) was derived, thus enabling the theory of certain types of mechanical vibration, notably torsional motion, to be put on a more rational basis.

By means of analogous elements it is possible to represent a mechanical vibrating system, provided it includes no bending elements, by an equivalent electric circuit. The author has been unable to discover any full description of the process, and the object of the present paper is to set out the principles underlying the procedure and to illustrate them briefly by examples.