The thermal aftereffect is proportional to the irreversible susceptibilitychi irrand thus has a peak value in the zone of coercive force. It follows a logarithmic time law of the typeDelta I= S cdot log t + constwhose constantSshows a linear increase with the absolute temperatureT. The quotientS/chi irris a material constant and proportional to the coercive force. Natural aging also follows a law of the formDelta B = S cdot log t + const, but is not proportional tochi irrand therefore does not have a peak value in the zone of coercive force. Natural aging disappears at the remanence and at the coercive force. The constantSof natural aging is proportional to the productI cdot H cdot chi irrand inversely proportional to the coercive force. The quotientS/chi irris, in this case, not a material constant and not proportional to the coercive force.