The total magnetic losses in a silicon steel transformer core have been measured at temperatures from 20° to 273°K using a variable‐frequency simple‐harmonic flux wave with magnetic field intensity amplitudes Bm from 2 to 10 kilogauss. The hysteresis, or frequency independent, part of the losses was obtained by graphical extrapolation. For all field intensities this hysteresis loss increases with decreasing temperature but the relative increase at any temperature is independent of field intensity. At all temperatures the hysteresis loss can be represented, within the accuracy of the data, by the empirical equation of Steinmetz Wh=w(T)Bmn. In addition, the exponent n in this equation was found to be independent of temperature. A figure showing the eddy‐current, or frequency dependent, part of the losses for 0.014‐inch laminations is also included.