It is shown, both theoretically and experimentally, that the reaction of eddy currents on the inducing tooth-ripple field, previously considered to be negligible, can be very large. This has an important effect on the subsequent calculation of loss in both turbogenerators and salient-pole machines.A comprehensive set of results, giving the pole-face field for the possible ranges of design values, is presented. These show that the two main parameters are the permeability of the pole material and the length of the air gap.The analysis on which the computation of results is based is quite general, and previous analyses of the tooth-ripple and related problems, apparently dissimilar, are correlated in the light of it.