While finding out the transient response of a direct current machine the field winding is represented by a resistance and an inductive react-ance of constant magnitude. The differential equa-tion of voltage around the field circuit is easily solved corresponding to any type of input, either step, rate or sinusoidal. The response in case of a step input or discontinuity is found to be expon-ential. This however, gives the response only app-roximately. The field winding changes its inducta-nce as the field current changes depending upon the saturation. Change in inductance can be found from the magnetisation characteristics of the winding. In the differential equation which is of the form Lf dLL + Rf if = V, Lg changes with if and hence dt we obtain a differential equation with variable coefficients. 3 methods of solution have been out- lined viz. (a) Point by point solution (b) Method of graphical integration. and (c) Actual solution of the differential equation representing magnetisati. on curve by an approximate equation. The method involving use of differential analyser has not been indicated as its use is limited by the availability of such a machine. In chapter I