The discrepancy between the theoretical eddy-current effects and the actual eddy-current effects in thick steel cores is investigated. By using thick cores the magnetic inhomogeneity arising from ferromagnetic domain configuration is of little consequence and the discrepancy may be attributed to an intrinsic time-lag effect in the magnetization process. This time-lag is measured and explained in terms of a localized eddy-current action associated with the dissipation of hysteresis loss. It was found that the time-lag depended upon frequency and was less important at high frequencies.