A simple and practical method has been developed for investigating certain important classes of dynamic systems, as represented, for instance, by a power system comprising synchronous or induction generating units, with prime movers, connected through transmission lines to receiving apparatus of the same character. The behavior of individual units, of course, can also be investigated, ¿such as the important case of determining the current pulsation of a synchronous motor driving a reciprocating compressor, or purely mechanical systemns involving moving masses and resilient members, such as beams, bus bars, etc., under the influence of suddenly applied load. In the present paper, the method is described and its application to a few of the possible cases is illustrated. The method is to have an ``equivalent electrical circuit'' solve the problem, and the oscillograph plot the solution. The idea is based on the fact that if the differential equation for an electric circuit is identical with that for the dynamic mechanical system in question, then the corresponding electrical quantities can be taken to represent quantitatively the actual mechanical quantities. The equivalent circuit can be easily set up, and oscillographic records of the voltages and currents constitute the plotted solutions. The chief value of the scheme lies not only in one's being able to easily solve a given complicated problem, but also in the facility with which the effect of change in design factors may be determined. The method is capable of considerable extension.